Читать книгу Chevrolet Small-Block Parts Interchange Manual - Revised Edition - Ed Staffel - Страница 7
ОглавлениеCHAPTER 1
CYLINDER BLOCKS
Block casting numbers are found on the ledge to the rear of the number-7 cylinder on the driver’s side of the small-block V-8s. The casting date of the block can usually be found on the rear of the case on the passenger’s side of the block on a ledge behind the number-8 cylinder. Some block casting dates are found at the rear on the driver’s side.
When you look at casting numbers and stamped numbers, in any part surface, sometimes the numbers are not as crisp and clear as they could be. Sometimes an 8 looks like a 3 or a 6. Also, individual digits in a number may be missing. The last digit may be missing or perhaps it just can’t be discerned by the eye. At times, Chevrolet ground off the cast number and replaced it with a number stamped by hand. These were rare instances, but they did occur.
Casting dates are usually expressed this way: “C 18 4.” In this example, the C means the month of March, 18 is the day of the month, and 4 is the last digit of the year. This last digit may mean 1964, 1974, 1984, or 1994, so you must also check the other characteristics of the block to determine in which decade and year it was made. Some parts have the decade and year cast on them; these identifiers look like this: “C 18 84.”
The block casting number “3896944” is found on a ledge at the rear of the block on the driver’s side. Sometimes you really need to check the numbers, as the last three digits are tough to make out in this example. The number on this block identifies it as a 283.
Chevrolet introduced new model years in September or October of each year, so when you see a casting date of “L 16 7” for example, this indicates a casting date used in the 1968 model year because it translates into December 16, 1967. A 1968-model Camaro assembled on January 6, 1968, might contain a number of parts that were cast in December 1967. Casting dates should precede hand-stamped engine assembly dates.
The engine assembly date and which factory assembled the engine are indicated by numbers and letters that are stamped into the block when the engine is assembled and placed into a specific vehicle at the factory. These stamped letters and numbers are usually found on a ledge forward of the number-2 cylinder on the passenger-side deck of the block. These stamped symbols are visible after the motor is assembled. The stampings show the month and day of the month the engine and vehicle assembly took place. At the end of the stamped symbols, the one-, two-, or three-letter engine suffix code identifies what type of motor it is, what type of vehicle the motor went into, what type of transmission was originally mated to the engine, and other features. Finally, on later blocks, there are also numbers that match the last five, six, or seven digits of the Vehicle Identification Number (VIN) that has been assigned to the vehicle.
The block casting date, which is the date the block was made, is found on a ledge at the rear of the block. This is not the date when the engine was assembled.
A block casting date of “L 5 6” is found at the rear of this block and translates to December 5, 1966. The “L” stands for the 12th month of the year.
The engine assembly date and the suffix code tell you about the original engine and vehicle in which the motor was placed. This information is usually found on a ledge on the front of the engine block on the passenger’s side. “VI027DE” tells you that this engine was assembled in the Flint, Michigan, plant (F); in the 10th month (October); on the 27th day. The “DE” suffix code in that year (1968, which is found with the block casting date code at the rear of the block), indicates a 307-ci small-block and manual transmission. Many later blocks also have a portion of the VIN stamped in this same location.
An example of a hand-stamped engine assembly date and suffix code looks like this: F0213ZE 023456, which translates into an engine assembled at the Flint (F), Michigan, factory on February 13 (the second month, 02, 13th day, 13)—years are not stated here—and a 327/250-hp engine (in 1965) with a manual transmission and A/C (ZE). The number also indicates that the car was a Chevy II that was the 23,456th vehicle assembled in the series.
All of these casting numbers and stamped numbers are consulted when someone wishes to determine if this is a numbers-matching engine and vehicle. Even more information is available on the trim tags, VIN plates, and hidden VINs and casting numbers, codes, and dates, which are found on other major powertrain components and vehicle frames. Whether the numbers match can be extremely important to someone who is buying a restored or restorable classic, and it can have an effect on the desirability, originality, and value of the vehicle. Knowledge of the correct casting numbers, date codes, suffix codes, and engine assembly code stampings help a buyer decide whether a 1965 Corvette with a 327/375-hp fuel-injected engine is an original numbers-matching car or not.
If the block has previously been decked (a machining operation to ensure the flatness of the block surface or to reduce the piston deck to block deck height to 0), these stamped letters and numbers may have been machined right off the passenger-side block deck surface and may no longer be visible. Engines that were replaced under factory warranty might use the CE suffix code or may not have any assembly or suffix code information at all. Also, criminals may have restamped the block in order to fake a more valuable or rare matching numbers block. Be careful! These days some rare vehicles with rare options have become high-dollar investments. It is possible to fake engine numbers, trim tags, VIN plates, and other documentation, all in an effort to increase the resale value of a vehicle.
Late-model blocks have their casting numbers on the rear ledge of the case along with the original size of the engine indicated in liters. This 350 block (5.7 liters) features a one-piece rear main seal and was obviously cast in Mexico.
Since the mid-1980s, many late-model small-blocks rated the engine size in liters (such as 4.3L, 5.0L, or 5.7L), and this number is cast into the ledge at the rear of the block on the driver side. Also, on late-model blocks, the last three digits of the block casting number are cast into each side of the block between the freeze plugs in large, easy-to-read numerals.
A number of changes to the blocks have occurred over the years. Some changes to keep in mind are: In 1955, the 265 block did not have an oil filter. The 265 also used a slightly different method of engine lubrication in 1955 and 1956. These 265 blocks feature two oil passage holes in the block at the rear cam journal to feed oil to the lifter galleries and heads. This requires the use of a rear cam bearing that has two matching holes in the cam bearing and a camshaft that has two flats ground into the rear journal of the cam itself. If you use an incorrect rear cam bearing or use a camshaft without the two flats in the rear cam journal, oil does not circulate to the lifter galleries and won’t get to the heads. This system was changed in 1957. The later blocks have an annular groove in the rear of the block itself and use a different-style rear cam bearing and rear cam journals without flats.
This early 283 block from 1955 to 1961 (left) was cast without a scallop shape at the bottom of the cylinder bores. This limits the crank stroke to 3 inches. Later small-blocks have the scallops at the bottom of each cylinder barrel to allow the use of longer cranks (right).
Block Casting Numbers
The 1961 283 block also had a tower in the front of the lifter valley. This tower connected to the oil filler tube that was present in intake manifolds until 1969, when the block casting was changed and the oil fill location was moved to the valve covers.
This 1967 283 block shows the rear of the block, which at that time had a cast-in tower and baffle assembly mounted in the lifter gallery for a crankcase ventilation system. Block castings were changed in 1969 to remove this tower.
Some blocks will show a number such as “010” on the rear of the block or on the front under the timing cover. This means that 1-percent additional nickel was used in the casting process. Sometimes only a single “020” is found, meaning that 2-percent additional nickel was used.
If you are using a manual transmission and mechanical clutch linkage, you may need to mount a ball and stud to the block in order to use the linkage Z-bar. Make sure that the block you use has the mounting boss in the correct location for your vehicle application. This block shows two; one near the filter boss and the other just to its left. Some blocks have multiple locations; some blocks have none. If you are updating to a hydraulic clutch or an automatic transmission, you don’t have to worry about this.
Chevrolet changed the location of the oil dipstick on different applications. Many simply went through the oil pan rather than the block. Other blocks may be machined for one on either the driver’s or passenger’s side near the head mounting deck. This block shows a driver-side-mounted dipstick.
The rear main seals of blocks used a rope seal from 1955 to 1958. During 1959 through 1985, they took a two-piece neoprene lip rear main oil seal. The circular, one-piece rear main seal was introduced in 1986 on production engines, although some replacement motors, crate engines, and Bowtie blocks still used two-piece rear main seals and matching cranks.
Front engine mounts were used in early blocks and were later replaced with side-mounted engine mounts. Some of the early blocks have no bolt bosses cast into the side of the blocks for engine mounts. If your block is from the 1950s, check it to make sure you use the correct front or side engine mounts.
The 265 and 283 blocks made from 1955 to 1961, which used 3-inch-stroke cranks, do not have any reliefs cast into the block where the block webbing meets the bottom of the cylinder barrels. The 1962-and-later 327 blocks have reliefs cast into the lower end of the block where the barrels meet the block webbing. This allowed the use of the longer 3.25-inch-stroke 327 cranks. If you have an early 265 or 283 block that does not have these reliefs, it is difficult to install a 3.25-inch or longer stroke small journal crank.
Small journal blocks made from 1955 to 1967 used 2.30-inch main bearing journals with a road draft tube boss at the rear of the lifter valley that mounted an oil separation canister in the lifter valley, which connected to the block and the road draft crank-case ventilation tube. Also, a tube cast into the front of the lifter valley mated to an oil fill tube on the front of the intake manifold. The 1969-and-later blocks eliminated the oil fill tube and the road draft tube. The oil fill tube on the front of the intake manifolds was also eliminated. Crankcase ventilation and the addition of oil were accomplished through the valve covers.
Many of the V-8 Chevy IIs made in the 1960s with 283 or 327 small-blocks have a unique block. Engine clearance in these 1962 to 1967 vehicles required that the oil filter boss on the driver’s side be moved up or recessed up in the block. In 1965 to 1967, the dipstick hole in these blocks was plugged and the dipstick tube went directly into the unique Chevy II oil pan.
If you intend to use a manual transmission in your vehicle, along with mechanical clutch linkage, and if the clutch linkage Z-bar requires a block-mounted pivot ball and stud, then the block you use must have a threaded bolt boss (usually near the oil filter–mounting boss) for the pivot ball and stud. Chevrolet placed this threaded boss on the block in a number of different locations. Some blocks have no threaded bosses; some blocks have only one threaded boss; and some blocks have a variety of bosses to fit a number of engine and vehicle combinations. Make sure the block you use has a threaded boss for the pivot ball and stud where you need it. An alternative is to use an automatic transmission or to use a hydraulically operated clutch linkage assembly.
The 350 engine was introduced in the 1967 Camaro. This 1967 Camaro 350 block used a larger main journal (2.45 inches) crankshaft. Other changes were made in the block webbing and bearing saddles to increase strength and to accommodate the larger journal cranks. Other large journal blocks in different displacements were introduced in 1968-and-later model years.
From 1970 through 1980, 400 small-blocks used 2.650-inch main bearing journal crankshafts and a slightly shorter connecting rod (5.565 inches). These blocks also used siamesed cylinder barrels with 4.125-inch standard bores in order to fit the increased cubic-inch displacement inside the original outside dimensions of a small-block V-8 case. These 400 blocks used externally balanced vibration dampers, flywheels, and flexplates.
These photos show the difference between the rear main seal designs: a two-piece seal (left) and a one-piece-seal (right).
This is the one-piece seal and mounting fixture that was used on 1986-and-later production small-blocks.
The oil dipstick entry location moved around over the years. The dipstick tube entry was usually through the driver’s side of the block deck and then into the oil pan. However, there are blocks on which the dipstick tube enters the block on the passenger’s side and then runs into the pan. On a few engine/vehicle combinations, the hole in the block that was meant for the dipstick was plugged, and the dipstick tube entered the side of the oil pan in order to clear obstructions such as the exhaust manifolds. Most interchange situations don’t cause a dipstick problem as long as you use an oil pan that matches the block dipstick’s mounting position—driver’s side or passenger’s side. If there is an obstruction that prevents dipstick entry into the block, you can replace it with a pan that allows the dipstick tube to enter directly into the side of the pan. This usually clears up any problems with stock exhaust manifolds. A few late-model Gen I blocks have a dipstick entry position on both sides of the pan rails. Take the time before you choose the parts to determine which ones you need.
The 1986-and-later production blocks switched to a one-piece rear main seal, which required other changes to crankshafts, oil pans, flywheels, flexplates, and engine block sealing surfaces, affecting the interchangeability of parts between the two-piece oil seal and one-piece oil seal motors. All production small-blocks with one-piece rear main seals are externally balanced. Some GM engines’ replacement crate motors and some of the performance Bowtie blocks still use two-piece rear main seals.
PN 14088556 is a stock aluminum rear seal retainer for one-piece rear oil seals on 1986-or-later production blocks with matching oil pan, timing cover, and pan gaskets. It also uses an adapter-to-block gasket (PN 12337823) and rear crank seal (PN 10088158).
PN 10051118 is a seal adapter that allows the use of a two-piece-style crank in a one-piece seal block with a one-piece-style oil pan and pan gasket. It requires a two-piece seal, adapter gasket (PN 12337823), and one-piece oil pan gasket (PN 14088505). The Moroso (PN 38315) seal adapter allows the use of a two-piece-style crank with a one-piece oil seal–style block, and it allows the use of an early two-piece-style oil pan, timing chain cover, and pan gasket.
The 1986-on model blocks machined for roller lifters and camshafts have taller machined lifter bores and three bolt bosses in the middle of the lifter valley to hold the lifter retainer fixture that was used with production Chevy hydraulic roller lifters.
Some blocks, such as this 1961 283, have dual-starter bolt patterns. Most blocks only have one pattern—either straight or offset.
When you have your block bored, make sure the final honing is done with a torque plate bolted in place. The plate distorts the cylinder walls in a way that is similar to the block distortion when the heads are torqued down on the block. The cylinders are round when honed and this helps improve ring seal.
Walk into your friendly Chevrolet dealer and order PN 10105123 and you’ll receive a bare, cast-iron 350 block. This is the 1986-on block with four-bolt mains, a one-piece rear seal, and clearanced for a 3.80-inch-stroker crankshaft. (Photo Courtesy Chevrolet Performance)
The 1987-and-later Gen I blocks were produced with taller lifter bores for use with factory-installed hydraulic roller cams and roller lifters with bolt bosses in the lifter valley for a roller lifter retainer spider. Flat tappet cams and lifters can be used in these blocks. The late-model hydraulic roller lifters are taller than a hydraulic flat tappet lifter and should be used with shorter factory pushrods for production roller lifters. All Gen II production engines use hydraulic roller cams and roller lifters.
Aluminum blocks weigh approximately 90 pounds bare. Cast-iron production blocks weigh about 150 pounds. The heavier Bowtie cast-iron bare blocks weigh approximately 185 pounds due to their thicker cylinder walls and decks and reinforced block webbing.
There are significant differences between the Gen I, Gen II (introduced in 1992), and Vortec small-block V-8s (introduced in 1996).
The large-diameter flywheels and flexplates (14 inches) that were used with one-piece oil pans may not fit some early engine and vehicle applications. The crossmembers and small-diameter bellhousings were originally made to be used with a 12¾-inch flywheel or flexplate. To fit the larger flywheels and flexplates, change the bellhousing or change to the smaller-diameter ones. Keep in mind that most blocks are drilled for two different starter bolt patterns, while some blocks have only been drilled for one starter mounting position.
Small-Block General Specifications
Configuration:
90-degree ohv V-8, with cast-iron or aluminum blocks and heads
Cylinders (Front to Rear):
Driver’s side: 1-3-5-7
Passenger’s side: 2-4-6-8
Firing Order (Clockwise on Distributor):
1-8-4-3-6-5-7-2 (Gen I, Gen II, and Vortec)
Computer controlled, no distributor
Crankshaft:
Gen I, II, and Vortec: Forged or cast, five main bearings, thrust on rear bearing
Crankshaft Journal Diameter:
1955–1968 small journal: Mains 2.30 inches, rods 2.00 inches
1967–1996 medium journal: Mains 2.45 inches, rods 2.10 inches
1970–1980 400 Crank: Mains 2.65 inches, rods 2.10 inches
1989-up LT5: Mains 2.76 inches, rods 2.10 inches
Crank Strokes:
Small journal: 3.0 inches and 3.25 inches
Medium journal: 3.0, 3.10, 3.25, and 3.48 inches
400 Cranks: 3.75 inches
LT5 350: 3.66 inches
Rod Length:
Forged steel 5.7 inches center to center
5.565-inch 400 rod
5.740-inch LT5 rod
5.940-inch Gen II 265-ci L99 V-8
Pistons:
Cast, hypereutectic, or forged aluminum slipper skirt design
Lubrication:
Full pressure oiling, wet sump
Some Bowtie blocks offered for dry sump
Block Bores:
3.50 to 4.126 inches
Bore Centerlines:
4.040 inches
Cubic-Inch Displacements:
262, 265, 267, 283, 302, 305, 307, 327, 350, 400
Compression Ratios:
8.0:1 to 11.0:1
Induction:
2-barrel 4-barrel
Inline 2 x 4 barrel
Crossram 2 x 4 barrel
Rochester Mechanical Fuel Injection
Throttle Body Fuel Injection (TBI)
Crossfire 2 x TBI
Tuned Port Fuel Injection (TPI)
Sequential Fuel Injection with mass airflow sensor
Engine Weight:
Approximately 550 pounds cast iron ■
Abbreviating Casting Numbers
It is common to abbreviate the casting numbers when speaking or writing about them. Rather than using seven, eight, or nine digits, the last three digits are commonly used when making reference to them. Thus, a block with casting number 3970010 is referred to as the “010” block. A cylinder head with casting number 340292 is also called a “292” head. Chevrolet rarely used the same last three digits in a similar part, so there is little duplication or confusion. Some parts with the same casting number were used in a number of different model years and engine combinations. Look closely at the casting numbers and casting dates. Sometimes they are difficult to see and an 8 may look like a 3. Sometimes the last digit in a number is missing, or rust, corrosion, grease, or dirt may obscure the number. ■
If you’re looking for a serious block to use as the foundation for high output, the 350 Bowtie cast-iron block is a good start. This block (PN 12480047) is CNC machined with four-bolt mains, splayed caps, tall lifter bores, and is set up for a maximum bore of 4.155 inches. (Photo Courtesy Chevrolet Performance)
On some of the early one-piece rear main seal production blocks, the boss for the mechanical fuel pump was cast into the block. However, the holes for the fuel pump pushrod and oil drainback were not always drilled. Check your block to see if these holes exist if you intend to use a mechanical fuel pump in your application.
Not all one-piece rear main seal blocks were set up for factory production hydraulic roller cams. Some late-model Gen I four-bolt blocks used in trucks contain the one-piece rear main seal but do not have the threaded bosses in the lifter valley that are used to bolt on the roller lifter retainer. These truck blocks used a flat tappet cam and a one-piece rear main seal.
To add to the confusion, a few one-piece rear main seal production blocks share the same block casting number but may have been drilled for either two- or four-bolt main caps. The “638” casting is one example. The only sure method of determining whether you are looking at a two- or four-bolt case is to remove the oil pan and take a look.
Production Cast-Iron Bare Blocks
PN 10066034 is a Gen I, 4-inch-bore, bare block with four-bolt gray-iron main caps. This block uses a two-piece rear main oil seal and its bearing saddles are sized for cranks with 2.45-inch main journals, non-siamesed, 4.00- to 0.060-inch bores, a 9.025-inch deck height, and a wet-sump rear cap.
PN 10105123 delivers a bare, non-siamesed block with 4.00-inch bores, a 9.025-inch deck, 2.45-inch main journals, a wet-sump cap, four-bolt straight main caps, and a one-piece rear seal. This Gen I block has a lifter valley that is machined for use with either factory roller or flat tappets and respective cams. The block weighs 181 pounds. This Gen I block was used with all ZZ 350 HO and CC 350/300 crate motors and is machined in the lifter valley for a factory hydraulic roller cam. The block can accept up to a 3.75-inch stroke crank.
Chevy Performance also offers a 383-ci block (PN 88962516) with a 4.005-inch bore, which has also been clearanced for a 3.800-inch stroker crankshaft.
Maximum Bore-Size Limits
There are limits beyond which a block should not be bored. In addition, replacement pistons are sized for particular bore sizes. Oversize pistons are generally available in Standard (Std.) 0.010-, 0.020-, 0.030-, 0.040-, and 0.060-inch sizes. Other sizes are available from custom piston makers, but the sizes given here are the most common.
If you are boring a block, stay within reason. As the bores are made larger, the actual thickness of the cylinder barrel wall becomes thinner, and as it gets thinner, it weakens and is subject to more distortion. Bore the block to the minimum amount needed to clean up the walls and still retain as much barrel wall thickness as possible. This helps the barrels maintain strength and resist flexing.
Bowtie blocks come with thicker barrel walls than production blocks, so even at large overbore sizes the walls are still thick enough to withstand the racing abuse these blocks no doubt see.
Also, when a block is cast, there is a remote possibility that the casting molds shifted when the molten metal was poured in. This results in a “core shift” in the finished block. Core shift in a block can cause many problems, one of which is that cylinder walls might be very thin on one side of the cylinder and thicker on the other. Lifter bores can be off of their correct positions and cause valvetrain geometry problems.
Engine Assembly and Suffi x Codes
When an engine is completely assembled and placed into a particular vehicle at the factory, an engine assembly date code and suffix code are stamped into the block casting. Usually, this stamped code is found on a ledge on the engine block deck located at the front of the passenger’s side of the block. These codes are visible to the eye even with the motor in the vehicle, although you may have to move the alternator if it is mounted on the passenger’s side to see the block ledge beneath it. These engine assembly and suffix codes can give you a great deal of information when you decode them.
The code may look like this: F0317ZM. The F stands for the Flint, Michigan, factory where it was made. The 0317 stands for the month and day of the month, in this case the third month 03, on the 17th day. Years and decades are not given in these engine assembly codes. The letters at the end, ZM, are the engine suffix code.
Various combinations of letters were used to indicate the vehicle model type, engine size, transmission type, and other things such as air-conditioning that were used on this particular vehicle when it was made. In this case, ZM was used on a 1966 Chevy II to indicate a 327 engine, a Powerglide automatic transmission, and air-conditioning.
On some blocks, parts of the VIN are also stamped onto this ledge.
These engine assembly codes, suffix codes, part casting numbers, and other features are used to determine whether a particular vehicle is an original “numbers-matching” vehicle. Numbers-matching original vehicles are sought by collectors. Keep in mind that it is possible to fake a numbers-matching vehicle in order to increase its value to collectors. This is particularly true of rare, and therefore, more-valuable vehicles that had a low-production-number part or combination of parts. Be careful!
Also, sometimes when a block is decked during a rebuild in order to ensure flatness or to reduce the deck height, the engine assembly and suffix codes can be machined right off a small-block by an inattentive machinist. ■
Another possible problem with boring is that the cylinder barrels may have porous sections. In this case, as the boring bar cuts into the cylinder wall to open it up, it may hit a porous section. If that happens, bore to the next largest bore, if you can. If the porous section is too deep, the block may need a sleeve or have to be scrapped. If you are already at the maximum bore size, you should obtain another block and start over.
In addition, rust inside the water jackets or on the piston side of the cylinder walls can eat into the wall thickness and cause a problem when the block is bored. If you find a block that has been sitting around outside for a while, be cautious. It may have features you desire, the price might be low, or you might be doing someone a favor by hauling the block out of wherever it is, but rust can ruin the usefulness of any block.
Sonic testing a block before boring can determine if there is a problem with core shift, porosity, or thin cylinder walls. Now, don’t get paranoid. These types of problems don’t happen often, but they do occur.
Blocks
262: The 262 has a standard bore of 3.671 inches and a stroke of 3.10 inches. These were thin block castings and should only be bored a maximum of 0.030 inch over, which would give a bore diameter of 3.701 inches. All of these Gen I blocks have two-bolt main caps and use 2.45-inch journal cast cranks. They were factory installed in 1975 to 1976 Novas and Monzas.
265: The Gen I blocks were made from 1955 to 1957 with a bore of 3.750 inches and stroke of 3 inches. They can be bored up to 0.125 inch over to a maximum bore diameter of 3.875 inches, which is the same as a standard-bore 283 block. All of these blocks have two-bolt main caps and use small journal 2.30-inch cranks. Blocks made in 1955 had no provision for an oil filter.
The Gen II 265, 4.3-liter V-8, introduced in 1994 in Caprice sedans and wagons can be safely bored 0.040 inch over. These are two-bolt blocks and use 2.45-inch main journal and 3-inch stroke cranks with a one-piece rear main seal. Don’t mix this block up with the Chevy 4.3-liter V-6 or the 5.7-liter Gen II LT1 motor that was used in the Impala SS.
The performance aftermarket offers a variety of small-block Chevy-based blocks. Dart’s Special High Performance (SHP) small-block offers some great features for performance enthusiasts. (Photo Courtesy Dart)
Another aftermarket source for blocks and engines is World Products. This is the Motown 350 cast-iron block, which is also offered in aluminum to save about 90 pounds.
The bottom end of the PN 10134400 aluminum race block is all business. The block is CNC machined with cast-iron sleeves and the crank is secured with stout splayed four-bolt steel main caps. (Photo Courtesy Chevrolet Performance)
267: This is another thin-cylinder-wall Gen I casting, which should only be bored a maximum of 0.030 inch over. This block has two-bolt caps and uses a 2.45-inch main journal crank. It had a 3.50-inch standard bore and 3.48-inch stroke and were made from 1979 through 1982.
283: Blocks originally having this displacement are a mixed bag. The blocks have a 3.875-inch standard bore and use a 3-inch stroke. The 1957 block castings can be bored a maximum of 0.060 inch over. The 1958 to 1962 blocks had thicker cylinder walls and can be bored 0.125 inch over to a maximum diameter of 4 inches. The 1963 to 1967 blocks went back to thinner cylinder barrel walls and should be limited to a 0.060-inch overbore. The 283 has two-bolt main caps and uses the small main journal 2.30-inch crankshafts.
302: These 4-inch standard-bore blocks can be bored 0.040 inch over. Many can go as large as 0.060 inch over, but this is cutting it thin and you may have problems. In 1967, the 302 used a small journal 2.30-inch crank with a 3-inch stroke and the block had two-bolt main caps. In 1968 and 1969, the Z28 302 used a 2.45-inch main journal crank and the block used four-bolt main caps.
305: These 5.0-liter Gen I motors are all medium-journal 2.45-inch blocks, and production blocks were only made with two-bolt main caps. They can be safely bored 0.040 inch, with some blocks going to 0.060 inch over. These Gen I blocks were introduced in 1976 with a 3.75-inch bore and 3.48-inch stroke. Blocks made from 1986 to 2003 have a one-piece rear main seal. A Vortec 5000 305 was introduced in 1996. Later-model blocks have been cast for use with roller cams.
307: Most of these 3.875-inch standard bores can be opened up 0.060 inch. I have heard of some being bored 0.125 inch over to 4 inches, but this is risky. If you need a 4-inch-bore medium-journal block, go find a good 350 core. These two-bolt blocks use a 2.45-inch main journal crank with a 3.25-inch stroke (the same stroke length as a 327). They were factory installed from 1968 until 1973.
327: These blocks were factory installed from 1962 through 1968 and have a 4-inch bore with a 3.25-inch stroke. They were all two-bolt blocks and the 1962 to 1967 blocks used small journal 2.30-inch crankshafts. The 1968 327 used a medium journal crank with 2.45-inch-diameter main journals. It can be safely bored 0.040 inch, with some blocks able to go up to 0.060 inch over.
350: The Gen I 350 first made its appearance in the 1967 Camaros. The Gen I and II cast-iron 4-inch blocks can be bored 0.040 inch over to 4.040 inches, and some blocks can go to 4.060 inches. All Gen I and II 350s used medium-journal 2.45-inch cranks with 3.48-inch strokes, and the blocks came in two- or four-bolt main cap varieties. Production blocks made from 1986-on have one-piece rear main seals. Many of the blocks made from 1987-on used roller cams.
400: The Gen I 400 is unique in that it has siamesed cylinder barrels. The standard bore of 4.125 inches can be increased safely to 0.040 inch over, with some blocks going to 0.060 inch over. This block came with either two- or four-bolt main caps from 1970 to 1980, and it was the only production motor to use a crankshaft with 2.65-inch main journal diameters and 3.76-inch strokes. The connecting rod length was shortened to 5.565 inches in order to fit everything in. These 400 engines were all externally balanced.
Cast-Iron Bowtie Blocks
PN 12480174 (casting number 10051184) has siamesed cylinders, 9.025-inch deck, with a 3.980- to 4.030-inch bore range. It has four-bolt mains, 2.45-inch crank journals, wet-sump oiling and a one-piece oil seal, and tall lifter bores. This bare block is CNC-machined and weighs 196 pounds.
PN 12480047 (casting number 100511184) is a Bowtie Sportsman Block with the same specs as the above block but it features a two-piece oil seal and weighs about 8 pounds more.
If you’re looking for a 350 main with a 400 bore size, Chevrolet Performance offers two Bowtie blocks to consider. Both feature siamesed cylinders with deck heights of 9.025 inches with a bore range of 4.117 to 4.755 inches. The mains are drilled at 20 degrees and accept nodular caps. The difference is in the rear main seals: PN 12480175 has a one-piece seal, while PN 12480157 features a two-piece seal. (Both blocks are based on casting number 100511184.)
PN 12480049 is a four-bolt block with 400 main and 350 bore size that has been CNC-machined to within +/-0.005-inch tolerances. It has splayed caps on the center three mains to accept four-bolts. The finished bore is 3.980 inches with a range up to 4.155 inches. The max stroke is 3.750 inches and has a wet oiling system. Another block is offered (PN 24502503) that includes steel caps rather than nodular like its sister block.
PN 24502650 was treated to a reduction in deck height (8.325 inches), so a short stroke/short rod, big bore motor was easier to build with improved high-RPM power, more direct intake port runner angles, compact size, weight reduction, and a lower center of gravity. The bore range is slightly larger at 3.980 to 4.185 inches and accepts a 283 crank journal for a max stroke of 3.250 inches. This block weighs in at a svelte 167 pounds.
Aluminum Bowtie Blocks
As with most things cast in aluminum versus iron, the major benefit is less weight. Chevrolet Performance offers several cast-aluminum race blocks with the same features as the cast-iron blocks, but they tip the scales at 100 pounds or even less. T-356 aluminum is used and CNC machined and fit with centrifugal spun cast-iron cylinder sleeves. Each of the aluminum blocks uses a two-piece rear main seal and has enlarged cam bosses allowing for larger cam bearings if desired. The wet oiling system is designed with priority on the mains, though the block cab be converted to a dry sump system with plugs.
PN 10134400 (casting number 10134996) offers siamesed cylinders with a 9.025-inch deck height. The block is set up for steel main caps with bolts at a 20-degree angle with the crank journal size at 400. The rough finished bore is at 4.117 inches with a max of 4.135 inches. There is also a similar block offered (PN 10185075), but it has main journal sizes of a 350 with a smaller bore starting point of 3.986 inches. The bare block weighs in at 90 pounds.
PN 24502495 is a tall-deck aluminum Bowtie case with a deck height of 9.525 inches and it can be decked to 9.0 inches. Deck thickness is 1.125 inches. Four-bolt splayed 8620 alloy steel caps are used on the center three caps, while the front and rear caps are straight four-bolt caps. Use 2.65-inch main journal cranks and a 400-style two-piece rear main seal. It has sleeves that are semi-finished at 4.117 inches, and it can be bored to 4.135 inches. The pan rails are spread 0.800 inch and take strokes of 4.00 inches without modification, strokes of 4.125 inches with minor grinding, and a 4.25-inch stroke with major grinding and modifications.
Additional tin or nickel is added to the cast iron in some blocks. These high-tin and -nickel blocks are very desirable. In this photo, the extra tin is noted on the rear face of this 350 block by the “010” signifying that 1 percent more tin was used to help the molten metal flow into the casting mold. The “020” indicates that 2 percent more nickel was used in this block, which helps make the cylinder barrels harder and more durable. These casting identifiers are also found on the front face of these blocks under the timing cover.
Buying a used small-block can be a gamble. Do you know the history of the engine? Has it been stored inside or in the open? Can you tell if a block or head is cracked? Also, you’ll need to research what the engine was used in to help make sure your new replacement parts work!
Bowtie Casting Numbers
Casting numbers generally can be used to identify most Chevrolet parts. However, I must caution you about two casting numbers that have been used on one Bowtie block and another casting number that has been used with some aluminum Bowtie 18-degree and 15-degree heads. I bring this up because you may be looking at a used casting and should know the differences.
On cast-iron Bowtie blocks, casting number 10051184 was used to indicate a block with standard lifter bore angles, and the same block and casting numbers were used to identify the SB2 block with SB2 aluminum heads. There are also other variations between PN 24502503 and PN 12480175 (which are both based on casting number 10051184). One block uses nodular caps (PN 24502503) while the other uses steel caps. Also, the “503” uses a two-piece seal, while the other uses a one-piece seal. One casting number but two completely different pieces. ■
This block uses big-block Chevy-type cam bearings (Federal-Mogul PN 1811M), and the camshaft tunnel itself is raised 0.391 inch from the standard location. This dry-sump block has priority main oiling. There is no provision for an internal oil pump. The oil filter boss has been deleted and a starter can be fitted to either side of the case. There is no provision for a mechanical fuel pump, either, because the fuel pump boss has been deleted. You need an aftermarket oil pan in order to fit the wider pan rails. Also, the camshaft should have big-block journal sizes and a longer aftermarket timing chain or belt to fit the raised cam tunnel.
Cylinder Sleeves
So you look at your cast-iron block and find that a cylinder barrel is cracked or has a window. What now? Some folks believe that when this happens the only thing left to do is cart the bare block off to the dump or local recycling center. An alternative is to try to save the block by using a repair sleeve.
A machinist overbores the cylinder barrel and then press fits a barrel sleeve into the block. The sleeve is then bored to size. It’s done all the time by competent machinists, and iron sleeves are used routinely in aluminum blocks. The question is: Is it worth the expense and bother?
If the motor is going to be used for stock or moderate street performance, then a sleeved cylinder works just fine. If the block needs more than one sleeve, you probably shouldn’t bother. It’s cheaper and easier to get another undamaged cast-iron block. However, if you’re working with a rare, numbers-matching block for a restoration project, it may be worth replacing more than one sleeve to retain the original numbers-matching engine.
Aluminum blocks, on the other hand, have iron cylinder liners in all of the barrels. Replacement sleeves are available from Chevy Performance or the aftermarket. PN 12480004 is a standard bore steel sleeve for late-design aluminum blocks, including PN 10134400. This sleeve has a 3.980-inch bore and can go up to 4.135 inches.
Freeze Plugs
Small-blocks use 1⅝-inch-diameter freeze plugs, which are available in brass as PN 94673017. Aluminum race blocks, however, use a threaded freeze plug with an O-ring seal. Other freeze plugs are available through the aftermarket.
Some 400 small-blocks used three freeze plugs per side. Other 400s had a boss in the middle of the side of the block for the third freeze plug, but the boss was not drilled. You can use this unique freeze plug design to help identify 400 small-blocks. Other small-block displacements only had two freeze plugs per side.
Cam Bearings
With the exception of the 1955 and 1956 265 blocks, which used a unique rear cam bearing and rear cam journal, Gen I production cases can use the following cam bearings: PN 474005 fits position number-1; PN 474006 fits in positions number-2 and number-5; and PN 474007 fits in positions number-3 and number-4. Remember, each cam bearing goes in a particular position front-to-back, since three different sizes are used. If you cannot find these older Chevy part numbers, turn to the aftermarket bearing companies.
Crate Engines—UPDATE!
Chevrolet has always offered small-block “crate motors” over the counter. That expanded tradition continues today and enables the buyer to purchase a complete or partial motor. These crate motors are all new from the oil pan to the valve covers and come with warranties. Chevrolet also realizes that a number of the currently offered late-model production engines appeal to enthusiasts who want to put these engines into earlier-model vehicles, whether they are classic hot rod coupes and trucks or to punch up the power in vehicles that never had factory-installed V-8s.
Likewise, the aftermarket performance industry has done what it can to provide engine parts that improve performance of late-model vehicles and still meet the required national, state, and local vehicle emissions standards. The following is just a sampling of what is currently available from Chevrolet Performance.
Before getting into the performance side of Chevrolet’s crate engine program, there are three economical choices if you’re simply looking for a quality replacement engine at a great price. PN 12681429 is a classic 350-ci engine designed to replace worn out small-blocks from 1973 to 1985. It is based on a new four-bolt block, flat tappet valvetrain, iron heads, and perimeter-style valve covers. For 1996–2002 replacements, there’s the L31 Vortec 5.7L PN 12530283 (4-bolt) and PN 12530282 (2-bolt) engine with cast-iron Vortec heads. Finally, there’s the 350 ci for 1985–1987 light-duty trucks as PN 12681430.
Now, let’s get into the performance side of the offerings, starting with the 350/290 Base (PN 193556580). Bang for the buck starts here with a four-bolt block with aluminum pistons working with 76-cc iron heads to deliver a safe 8.0:1 compression ratio. The engine is rated at 308 hp at 5,100 rpm and 347 ft-lbs of torque at 3,900 rpm. The engine is basically a long-block but Chevy offers a Deluxe model (PN 19355659) that includes a 4-barrel intake complemented with chrome valve covers and air cleaner.
PN 19955662, the 350 HO Turn-Key engine, is topped with a set of iron Vortec heads fit with 1.94/1.50-inch valves. Compression is set at 9.0:1 and a flat tappet cam is supplied with peak power coming on at 5,100 rpm with 333 hp and 381 ft-lbs of torque. The Turn-Key crate engine comes with a 4-barrel intake, HEI distributor, a Holley carb, fuel pump, plug wires, and a complete front serpentine belt assembly including a new alternator, power steering pump, and air-conditioner compressor. A long-block package is also available as PN 19355660.
Next in the crate list is the SP350/357 that delivers 357 hp and 407 ft-lbs of torque. Based on the same block and Vortec heads as the 350 HO, the addition of a hydraulic roller cam with a little more lift and duration provides a little more kick to the output numbers. The Base model (PN 19367080) is basically a long-block; a Deluxe model (PN 19367082) is supplied with an intake, carb, HEI distributor, damper, and flexplate. To make it even easier, the Turn-Key model is supplied with even more, including the starter, carb, and a complete front accessory drive.
The next level of small-block offered by Chevrolet Performance is the SP350/385 rated at 385 hp at 5,600 rpm. The Base model (PN 19417624) is built on a four-bolt iron block foundation and features a forged-steel crankshaft, an aggressive hydraulic roller cam, and a beefed-up valvetrain. The big difference comes through the aluminum heads originally based on the proven Fast Burn design. A Deluxe version is also offered with a complete front drive as PN 19417623.
If you’re looking for a high-output crate engine equipped with a reliable EFI system, the classic Ram Jet 350 is still available as PN 19417619. The EFI intake gives a nod to its heritage with a resemblance to the original Rochester mechanical fuel injection system. The EFI is managed by a compact MEFI controller that needs no tuning or programming. The combination delivers a stout 396 ft-lbs with 345 hp.
The top-of-the-line ZZ6 crate engine is the ZZ6 platform, which produces more than 400 hp and torque. This package is the latest in the proven ZZ platform and is available as PN 19417576 for the Base model followed by a Turn-Key, an EFI Deluxe package, and an EFI Turn-Key model. ■
Chevrolet Performance offers a number of crate engines ranging from long-blocks to complete turn-key packages that include a carburetor (or even EFI), front accessory drive, plug wires, and more. This example is the SP350/385 Turn-Key package available as PN 19417623. (Photo Courtesy Chevrolet Performance)
Discontinued and Obsolete Parts
Say you decide that you need a particular part and you check with Chevrolet Performance or even General Motors and find that the part is no longer made. Before your frustration level forces you to contemplate burning your project down, remember that the small-block V-8 was introduced in 1955—some of the parts may be up to 60 years old. As demand lessened for certain pieces, Chevrolet dropped production of those and went on to other designs. If you must have a certain part or casting number, part of the fun will be searching for it.
Before you start, make sure that you know everything you can about the identification of that part, so you know it when you see it. Also, find out what it is worth. Get an idea, before you buy, of the usual price range of the part, new and used. Swap meets, junkyards, and the internet can lead you to the parts you need. However, don’t rely on the description given by the seller. Sometimes the seller doesn’t know what he has or has misidentified the part either intentionally or innocently. Of course, most times the seller knows exactly what he has.
Keep trying. It never ceases to amaze me when I consider what some folks have stashed away in their garages and storage sheds. Be prepared to buy a part you need one week and then to find the same part the following week for one-tenth the price. It happens. I was searching for a particular intake manifold with a particular casting number and casting date to restore a numbers-matching Corvette. I found one in another state and was willing to pay the price, $150, to get it. I was happy to finish the project. Two weeks later, I went to a swap meet. In a pile of intakes, I found the same manifold, with the same casting numbers I needed for $10. One man’s treasure was another man’s junk.
Many parts are still available over the counter from a Chevrolet dealer, so try them first. If you don’t succeed there, try a more specialized dealer or an authorized and licensed aftermarket supplier. Often, these parts are produced using the exact same blueprints and tooling that were originally used to make the parts. Not everything is being reproduced, but with more than 16,000 listed part items, one of them may have what you need. ■
ZZ6 350 HO Crate Motor
The crate motor business is booming, and one of Chevrolet’s most popular crate engines has been the ZZ-series of Gen I small-blocks. The latest version is the ZZ6 which delivers more than 400 hp and torque to match. Think about that, this crate engine delivers more power than any 350 small-block ever installed in a production vehicle! The ZZ6 is available in several iterations:
PN 19417576 is the base model and is supplied with an externally balanced flexplate, aluminum heads and intake, HEI distributor water pump, and damper topped with a set of distinctive center-bolt valve covers. (A short block is also available as PN 12670966.)
PN 19417622 is known as the ZZ6 Turn-Key package and is supplied with the base-model components along with a 770-cfm Holley carb, starter, fuel pump, air-conditioner compressor, power steering pump, alternator, plug wires, and a serpentine belt drive system.
Chevrolet Performance also offers two electronically fuel injected versions of the ZZ6. PN 19368149 is the EFI Deluxe engine that is topped with a port fuel injected intake with a throttle body mounted in place of the carb.
An engine control unit (ECU), harness, and WB02 are supplied to finish the wiring and to get the engine fired up without the need for third-party tuning. A Turn-Key option is also offered for the ZZ6 EFI package, which comes with the accessory drive kit and more. ■
The ZZ6 crate engine from Chevy Performance is the most powerful “production” small-block of all time with 405 hp and 406 ft-lbs. It is offered in a base model, a Turn-Key version, EFI Deluxe, and a Turn-Key EFI package. (Photo Courtesy Chevrolet Performance)
Vortec 5000 and 5700 Engines
In 1996, Chevrolet introduced the Vortec 5000 RPO L30 305-ci and Vortec 5700 RPO L31 350-ci engines and made them available in full-size trucks, Suburbans, and Blazers. These are enhanced Gen I one-piece rear main seal small-blocks, but they feature a number of changes that improve performance. All of these engines have steel hydraulic roller cams and roller lifters, and the blocks have minor lifter-bore changes to use roller lifters along with bolt bosses in the lifter valley to bolt the spiders, which help retain the roller lifters in their respective bores.
The Vortec cast-iron cylinder heads have revised, larger (170-cc volume) intake port runner dimensions and the combustion chambers have been changed to help increase compression. The 64-cc heart-shaped chambers have straight plugs, but the plug bosses move the plugs higher and closer to the chamber roof. The L31 head uses 1.94/1.5-inch valves with pressed-in rocker studs. The intake port openings are 0.080-inch taller than those on previous standard-production Gen I heads. The intake manifold bolt holes in the Vortec heads are positioned at 90 degrees to the head/manifold surface, but the bolt spacing is different and only four bolts are used on each side to mount the two-piece Vortec intake manifold. You must use a revised Vortec intake manifold gasket when using Vortec heads and related production or aftermarket intake manifolds.
Sequential electronic fuel injection with a mass airflow meter is used along with a two-piece intake manifold, which has an aluminum lower base piece and a composite plastic material upper half. Static compression has been increased and the coolant system has been revised to provide better bank-to-bank coolant flow balance. The coolant passages at each end of the heads are larger.
The vibration dampers on Vortec 5000 and 5700 motors incorporate a crankshaft trigger ring for their electronic ignitions and are not interchangeable with other Gen I engines. The Vortec small-block engine blocks also have an additional coolant bypass hole that is not used in other earlier Gen I powerplants.
The 1996 Vortec 5000 305 has increased output to 220 hp at 4,600 rpm and has 285 ft-lbs of torque at 2,800 rpm. The Vortec 5700 has 335 ft-lbs of torque at 2,800 rpm and delivers 250 hp at 4,600 rpm. These engines can still readily be found in donor vehicles and can make a good powerplant for hot rods and pickups, but you need to make sure to use the specific Vortec components from Chevrolet or the aftermarket. ■
You may have heard that a number of race engine builders are using roller cam bearings in their maximum-effort, “take no prisoners” engines. These are entirely unnecessary in stock and even most race engines.
Main Caps
Gen I and II small-blocks have been offered with two- or four-bolt main caps. Most four-bolt main cap blocks have a two-bolt front cap and a two-bolt rear main cap. Now, before you run out and look for a four-bolt block or upgrade from two-bolt caps to four-bolt caps, keep in mind that a two-bolt block can withstand up to 500 hp, especially if you use quality main cap studs and nuts instead of the stock main cap bolts. The two-bolt bottom end has to be right, but it is often used in short-duration motors.
For stock street use and some performance and race use, a two-bolt block is more than adequate. If your power levels are going to be higher than this or if you are going to use large doses of nitrous, high-boost turbocharging, or supercharging, then go to a four-bolt block.
The Gen I and II main caps themselves are made of gray iron, nodular iron, or steel. Most factory-installed production blocks use two- or four-bolt gray-iron main caps, although some had nodular-iron caps (the nodular main caps have an “N” cast onto their surface). Most are straight caps, meaning the bolts enter the block surface at 90 degrees. However, some Bowtie four-bolt main steel caps are splayed, which means the two inner bolts enter the block at 90 degrees, while the two outside bolts enter the block at 70 degrees. They are splayed 20 degrees from perpendicular. The splayed caps provide more bottom end strength and perch in a place in the block that is subject to less distortion.
SB2: Short Name, Big Design Jump
In 1996, Chevrolet offered an all-new Gen I–based small-block racing engine called the SB2. It’s new-design block, aluminum cylinder heads, and two-piece, single, 4-barrel intake manifold made up the bulk of the changes. To make matters a little more confusing, Chevy introduced an SB2.2 engine design with further updates before being updated with the RO7 at least in NASCAR competition in 2007. Unless you’re really searching for something unique to run in your hot rod or high-revving weekend warrior, there’s not a big call for these engines any more. However, having something unique is what makes hot rodding fun, so let’s take a quick look at what made the SB2.
The cast-iron block (PN 24502600) is based on the proven Bowtie 1184 block design. The splayed four-bolt blocks feature revised lifter angles and lifter bore locations that work with the new SB2 heads. The lifter bores could be enlarged to 0.875 inch and the cam bearing bores were sized for big-block Chevy-style cam bearings.
The SB2 aluminum heads featured non-siamesed mirror port intakes and revised raised intake runner angles, which each point directly toward the intake manifold plenum and carb. Also, the locations of the intake and exhaust valves have been changed from the standard production sequence. The valve sequence on these SB2 heads is I, E, I, E, E, I, E, I. This valve sequence calls for a different camshaft, and aftermarket cam makers are set up to produce the cams and left- and right-bank pistons you need.
SB2 heads can be used on a stock production block or Bowtie block, but you need the updated camshafts and 0.180-inch offset roller lifters in order to maintain rocker arm geometry. The raised intake port runners along with the SB2 intake manifold runners have been repositioned so that there is a direct line from the intake manifold plenum to each cylinder. The intake port openings are almost 1/2-inch higher than those found on the 18-degree, high-port Bowtie race heads.
Extra-long-stem 2.15/1.65-inch-diameter valves (5.550 inches overall) are required. These are slightly longer than those used on the 18-degree, high-port Bowtie heads. The SB2 uses a 1.950-inch spring installed height. The intake valve angle is decreased to 12 degrees, and the exhaust is angled at 8 degrees, toward the bore centerline. On the CNC-prepared SB2 head (PN 24502560), the combustion chamber is shallow and measures 38 cc on the CNC-prepped head, which gets you 15.0:1 static compression with a flat-top piston and 358 ci. The chamber can be opened up farther to 53 cc to run a 9.0:1 compression ratio.
The SB2’s exhaust ports are raised and have a siamesed-port exit design with more coolant passages nearby to aid in cooling. The exhaust port openings feature revised exhaust header bolt patterns that are unique to the SB2 heads and require non-traditional tube header flange bolt holes to match.
Use head gasket PN 10185054 with these SB2 heads. The head calls for the standard head bolt pattern, but because of the revised port locations, some of the bolts pass through openings in the rocker arm valley and into the port runner floors. Screw-in AN plugs with O-rings are used to block off the head bolt access holes in the rocker valley.
The special, eight-bolt, cast-aluminum valve covers provide oil galleries and spray bars that can be added to shower the valve springs with pressurized oil. These help cool the valve springs to increase race durability.
The two-piece intake manifold uses a separate lower valley cover that provides for the coolant crossover, thermostat housing, and distributor mounting and keeps hot oil in the lifter valley off of the intake runners. The upper dry manifold runner spider and the single Holley 4-barrel carb with an open plenum are unique to the SB2 head intake ports and offer the advantages of easy removal of the upper manifold plenum and intake runners without having to remove the distributor or drain any coolant. ■
Keep these tips in mind: Whenever you replace the original main caps, you must have the new caps fitted to the block saddles in order to properly register the caps. The new caps must then be precision align-bored and align-honed in order to ensure that the crankshaft is properly centered in the block and that it is square with the front and back of the case and perpendicular to the cylinder barrels. Not all automotive machine shops are properly set up, or experienced enough, to do this kind of work. Make sure you patronize a shop that has the equipment and expertise to reliably align-bore and align-hone your engine.
When a block is align-bored, the distance from the crank center-line to the camshaft centerline may be altered. This alters the length of the timing chain needed on that block. Competition Cams, Cloyes, and other companies offer timing chain sets that have shorter chains to accommodate align-bored blocks. If you install a new standard-length timing chain and gear set on an align-bored block, there is so much slack in the new chain it looks like a used one out of a taxicab engine with 300,000 miles on the clock.
Places to Look for Small-Block Cores
Everybody knows that Chevrolet has been making small-block V-8s since 1955, but they also stopped putting them in production vehicles in the late 1990s as the Gen III took over. Finding rebuildable Chevy engine cores is not difficult; millions have been made. They have been used in passenger cars, station wagons, muscle cars, police and taxi vehicles, hot rods, boats, RVs, school buses, race cars, heavy-duty trucks, generators, and irrigation pumps. Some guys have even stuck them in airplanes.
Keep in mind that other GM divisions have used Chevrolet small-blocks to power some of their vehicles. Chevy 305 and 350 engines have been factory installed in Pontiac, Buick, Oldsmobile, and Cadillac cars. The 1977 to 1980 models are good places to look for carbureted Chevy small-block motors in BOP cars, and 1990 Cadillacs used a fuel-injected Chevrolet Gen I 350 with a roller cam and a one-piece seal. In 1991, Cadillac also used a 305 with fuel injection, hydraulic roller cam, and a one-piece rear main seal. Some Pontiac Firebirds in the 1990s have used Chevy LT1 Gen II motors.
Now don’t confuse these Chevrolet-made engines with the 350-ci motors that Pontiac, Oldsmobile, and Buick designed and used in their cars. What am I saying? Any Bowtie lover can spot a Chevy small-block in a junkyard or an arroyo from 2 miles away, no matter what’s wrapped around it. ■
It is a good idea to mark each main bearing cap (and rod cap) with a stamped-in number before you take an engine core apart. Each cap must go back into its respective position and the correct direction when it is reassembled. The factory puts an arrow on each cap to show the “front” direction. However, the caps are not numerically stamped. You need to stamp them before disassembly.
Main Bearings
Main bearings are generally available in the following sizes: standard (Std.), 0.001, 0.010, 0.020, 0.030, and 0.040 inch. When a crankshaft is checked for wear, it may be necessary to grind the crank journals undersize in order to restore the journals to their correct roundness and to remove scratches. An oversize bearing must then be used to keep the required running clearances.
The most important thing is to make sure that the bearing surfaces are spotlessly clean—both the bearing itself and the bearing saddles in the block and the main caps. Check the clearances and follow the clearance recommendations. Chevrolet recommends main bearing clearances of 0.002 to 0.003 inch with a crank thrust clearance (also called crank end play) of 0.005 to 0.007 inch. If the crank has been reground, make sure that the radius from the crank cheeks to the journal are not going to interfere with the side edges of the bearing. Chamfered-edge bearings are available to clear cranks with large journal radii.
Chevrolet Performance offers a main bearing kit for a standard 350-ci engine as PN 12499102. Always use a main bearing set that has a groove cut in the half of the bearing that fits in the upper position in the bearing saddles of the block. The lower bearing half should not have a groove, and it fits in the main bearing cap. Do not use fully grooved bearing shells.
Block Dowel Pins
Sometimes when you acquire a block, a number of the dowel pins are missing. Here are the GM replacement parts for Gen I blocks:
| Block Dowel Pin Part Numbers | |
| Part | Part Number |
| Rear Block/Transmission Dowel Pins | 01453658 |
| Block Deck/Head Locating Pins | 585927 |
| One-piece Rear Oil Seal Housing/Block Locator Dowel Pin | 9441003 |
Some folks wish to offset the cylinder head locations from their original blueprint location for racing purposes. Offset head locator pins are available from aftermarket suppliers. However, this is not something a novice engine builder should try. At times, the block is misaligned to the transmission bell-housing locator pins on the rear of the block. Offset block/transmission dowel pins are also sold on the aftermarket.
Generation II LT4
In 1996, Chevrolet also introduced the LT4 350 small-block V-8 as an engine option in the 1996 Corvettes. This Gen II small-block 350 engine has a number of changes when compared to the 1992 to 1995 Gen II LT1 350, which has 300 net hp and 330 ft-lbs of torque in production vehicles. The 1996 production LT4 engine is rated at 330 net hp, and used revised aluminum heads with 2.00/1.55-inch lightweight valves. The exhausts are hollow stem valves that are partially filled with a mixture of sodium and potassium to improve valve cooling and reduce weight. Static compression is 10.8:1 (the Gen II LT1 has 10.4:1) with the small chamber LT4 aluminum heads and revised pistons that have the smaller valve reliefs.
The LT4 heads (PN 12555689 or 12363287) have intake ports that are raised 0.100-inch higher than those found on the 1992 to 1996 LT1. The port contours have been reshaped and improved for more flow and increase the intake port volume to 185 cc. The exhaust port contours have been changed on the LT4 head for smoother flow. Stud-mounted, self-aligning Crane roller rockers with a 1.6:1 ratio are used along with single-coil 110/260-pound spring-pressure valve springs. The LT4 head (PN 12555689) uses a non-adjustable net lash shouldered rocker arm stud. A steel roller cam and hydraulic roller lifters increase the capabilities of the valvetrain to 6,300 rpm.
This motor used reverse-flow cooling and its heads can be interchanged onto the LT1 block, provided that you use the production LT4 electronic TPI manifold. Use the new-design LT4 intake manifold gaskets, which fit the revised intake manifold bolt-hole spacing and bolt angles. The LT4 uses a one-piece rear main seal crank, which is externally balanced, and 5.7-inch powdered metal rods. These engines may now be even more rare than the SB2 race engine. ■
Used Engine Blocks
If you are about to buy a used block, here are some things to think about before buying: How has the block or complete engine been stored? Has it been kept inside in a clean, dry place or has it been sitting outside? Has it been covered up? Why is it being sold? Did a rod bearing spin? Was it burning large amounts of oil before it was pulled out? Is it covered with rust, dirt, or 200,000 miles of grease? If water was left in the block when it was stored or if rain or snow has gotten into it, has the block suffered a freeze crack? Some cracks are practically impossible to spot when the block is covered with rust, oil, grease, or who knows what. If the crank and rods are still in the block, can you turn the motor over? Is it locked up or does it turn over smoothly?
Check the casting numbers and dates. What do they tell you? If the heads are off the block or if the seller lets you remove the heads, check the bore of the motor. Has the block already been bored 0.040 inch over or larger? Are the cylinder walls clean, rusty, or cracked?
Look at the threaded bolt holes on the block. Have any of the threads been stripped? Are bolts broken off in the holes? Are all of the main bearing caps still on the engine? Are dowel pins missing?
Some problems may not be found on a used block until you take it to a machine shop and have it cleaned. You may find cracked cylinder barrels, cracked water jackets, or cracks caused by broken connecting rods hitting pan rails, oil passages, or cylinder barrels. The main caps may be mismatched or from another block.
Some of these problems can be fixed. Cylinders can be sleeved, threaded holes can be heli-coiled, and cylinders can be bored out and cleaned—up to a point. Some problems cannot be fixed. Cast-iron blocks with cracks in the outboard water jackets, with major damage from a broken connecting rod, or with more than one cracked cylinder barrel need to go directly to the dump or metal recycler or back to the guy who sold it to you.
The point is, there are times when the cost of fixing a used block is too high. Keep looking for a block that doesn’t need major repair. Try to find a used engine that is still running in a vehicle so you can hear it and maybe drive it to get a better idea of its condition. Millions of Chevy Gen I and II small-blocks are out there, so you shouldn’t have any trouble finding a good, rebuildable core motor with the features that you want.
