Читать книгу Chevrolet Small-Block Parts Interchange Manual - Revised Edition - Ed Staffel - Страница 9

CHAPTER 3

ROTATING ASSEMBLIES

Often when you look at a crank counterweight to check the casting number, only the last four digits of it are there. Check it against the crank casting number list by looking at the last four digits of those numbers. Casting dates are also found on crankshafts.

The 265, 283, and some 302 cranks use a 3-inch stroke with small journals. The 1968 and 1969 302 cranks have a 3-inch stroke with medium journals.

The short-lived 1975 to 1976 Gen I 262-ci engines had a cast crank stroke of 3.10 inches with medium journals.

The 307 and 327 engines used crank strokes of 3.25 inches. All 307 cranks are medium journal cranks, while 327 cranks were made in both small and medium journals. You can use a 350 medium journal four-bolt block, then use a rebalanced 307 cast medium journal crank to build a four-bolt 327-ci engine.

The 267, 305, and 350 cranks used a 3.48-inch stroke length with medium journals.

The 400 engines that were made from 1970 to 1980 used larger-diameter-crank main journals (2.65 inches) and the same rod journal size as medium journal cranks (2.10 inches) but with a crank stroke of 3.75 inches. These cranks require external balancing by using specific vibration dampers, flywheels, or flexplates for the 400 engine. This is also true if you build a popular non-factory combination: a 400 crank with the main journals cut down to 2.45 inches in a 350 block. You must use the externally balanced 400 damper and 400 flywheel or flexplate. It is possible to internally balance a 400 crank by having an experienced machine shop add heavy metal slugs to the counterweights. Do not use an externally balanced 400 damper, flywheel, or flexplate on an internally balanced engine. I bring this up because on several occasions, folks have shown up at my shop with a running 350 small-block that had a huge vibration or a newly rebuilt 350 that had broken some rods or suffered some other major disaster. When we checked the engine, I noticed that the 350 engine had a 400 vibration damper or a 400 flywheel or flexplate. The owners didn’t know the difference, and they had unknowingly pulled a tired 400 engine out of the vehicle, replaced it with a rebuilt 350, and used the 400 damper and flexplate on the new internally balanced 350 engine. It doesn’t work for long.

Crankshafts have casting numbers and casting dates so you can learn more about what you have or are looking at.

A forged 350 steel crank (casting number 3941182) has casting numbers on the front counterweight. However, only three digits (182) are discernable here.

In 1986, Chevrolet introduced the one-piece rear main oil seal and made related changes in cranks, oil pans, gaskets, and blocks. The medium journal cranks, used in one-piece seal blocks, are all externally balanced and require the use of matching 1986-or-later flywheels and flexplates. The flange on the rear of the new-style cranks was changed to fit the one-piece seals, and the bolt pattern for flywheels and flexplates was reduced to a 3-inch diameter from the 3.58-inch bolt pattern used on two-piece seal cranks from 1955 through 1985.

Cranks were balanced with whatever size engine and related rotating components it received at the factory. A 307 crank is not balanced the same as a medium journal 327 crank, even though they physically interchange with each other and have the same stroke. If you mix and interchange rotating parts from different engines, have the rotating assembly rebalanced.

Some cast, 2.45-inch main journal, 3.48-inch stroke, two-piece cranks have the same casting number (3932442), but are balanced differently. Cast cranks used on 267, 305, and 350 motors should not be interchanged from one engine size to another because of possible balancing problems, even though they have the same stroke and physically interchange in medium journal blocks.

Two-Piece Seal Cranks

Since Chevrolet switched to a one-piece seal more than 30 years ago, it does not offer a new crankshaft for the original two-piece seal blocks. Following are some of the more popular crankshafts that were available to help in your search or identification of used or NOS cranks that you may come across.

PN 3932444 is a nodular cast-iron 350 Gen I crank with a 3.48-inch stroke. This crank is used with a two-piece rear main oil seal and has 2.45/2.10-inch journals.

PN 24502460 is a raw 5140 alloy forging used to build large journal cranks of various journal sizes and strokes. This crank is no longer available from Chevrolet.

PN 3941180/casting number 1182 is a 1053 forged steel crank with a 3.48-inch stroke and 2.45/2.10-inch journals.

PN 10051168 is a 4340 alloy, raw, non-twist forging with 3.20- to 4.0-inch strokes possible. It comes with 2.900-inch unmachined journals that can be cut to fit 400 small-block 2.65-inch main journals.

PN 3951527 is a cast 400 crank, 3.75-inch stroke, 2.65/2.10-inch journals in ductile iron. It requires external balancing by using an appropriate 400 front damper and 400 flywheel or flexplate.

Some crank surface treatments, such as nitriding, only penetrate the surface of the metal a few thousandths of an inch. If the crank journals are later cut or reground, the treated surface may be cut or ground off and the crank does have to be retreated. Some aftermarket crank makers use a hardening treatment that penetrates 0.010 to 0.015 inch and is still there after a reduction in journal diameter of 0.010 inch.

One-Piece Rear Seal Cranks

All 1986-and-later one-piece rear main oil seal cranks are externally balanced, have medium-size journals, and have a smaller bolt circle (3.0 inches) pattern on the rear crank flange. This requires the use of matching late-model flywheels and flexplates, which have mounting bolt-hole patterns that match the cranks for one-piece rear main seal engines. Flywheels and flexplates for two-piece rear main seal cranks do not interchange with one-piece seal cranks.

This is the one-piece rear main seal crank, which first came into use in 1986 on all production engines. Compare the rear flange area to the earlier Gen I two-piece rear main seal crank.

Shown are the rear flange and journals of a Gen I crank that uses a two-piece rear main seal.

PN 14088526 is a nodular cast-iron crankshaft for use with a one-piece rear main seal. This is a 3.48-inch stroke crank with 2.45- and 2.10-inch journals.

PN 14096036 is a 1053 alloy forged crank with 2.45/2.10-inch journals and 3.48-inch stroke. The original ZZ1 and ZZ2 350 HO crate engines received this crank, while the ZZ3 and ZZ4 engines used PN 14088533. Both are discontinued.

PN 14088533 is a 1053 alloy forged crank with 2.45/2.10-inch journals and 3.48-inch stroke. It requires a one-piece rear main oil seal. This crank was used in the ZZ3 and ZZ4 crate engines and on the ZZ3 short-block partial assembly.

PN 12670965 is also a 1053 forged steel crank that is used in ZZ5 and ZZ6 engines as well as in post–November 1998 ZZ4 engines. It must be used with rod PN 10108688 and piston PN 10159436.

PN 12489436 is a forged 4340 steel crank used to produce 383 ci with a 3.800-inch stroke. Mains are standard 350 size and 2.100-inch rod journals.

Used Cranks

When you are looking at a used small-block crank, determine if it is a cast or forged crank. You can expect to pay more for a forged one due to added strength. The cast crank has a thin parting line on its throw arms, while a forged crank has a much thicker or wider parting line.

Check the casting number and casting dates to determine what stroke it is. Does it use a one-piece or two-piece rear main oil seal? Measure the rod and main journals. Has the crank been previously cut down? Machine shops that recondition cranks usually stamp the amount they have cut the crank on the front crank throw arm. If your measurements show that the crank journals have been previously cut more than 0.010 inch, walk away. You can find another one.

Are the threaded holes in the rear flange stripped? Has the drilled hole for the pilot bearing at the rear of the crank been elongated or damaged? Has the thrust surface on the crank been worn or damaged? How about the threaded hole in the crank front snout? Some early crank snouts are not drilled or tapped for a vibration damper retention bolt. You can get the snout tapped and threaded for the bolt at a machine shop. Also, some early cranks that were used in automatic transmission cars did not have a hole drilled in the rear of the crank for a manual transmission pilot bushing.

Remember, when you get the crank to the machine shop, ask the crew to clean it, check for cracks and straightness, clean out the threaded holes and oil passages, and possibly have it ground and micropolished. If any of the journals have been damaged, you may be able to have the journal welded or chromed then cut back to acceptable size. However, you need to compare the cost of fixing a damaged crank to the cost of buying an undamaged one. At some point, it’s cheaper and easier to find an undamaged used crank or to buy a new one than to repair a damaged one.

Check the crank journal diameters to see if the crank has been previously cut and to determine the size of the bearings you need.

Cast Versus Forged Cranks

Chevy stock cranks are either nodular cast iron or forged steel. To figure out which yours is, check the parting line, which is left from the molds when the crank is poured. A cast crank has a thin parting line, while a forged crank line is thicker or wider. Tap a crank lightly with something hard, and a cast crank emits a thudding noise. A forged crank rings like a bell; it is a quite distinctive sound. Of course, you can also check the casting number.

Some people who build high-performance motors believe that they must have a forged crank and that cast cranks just don’t cut the mustard. They would rather shell out the extra money for a forged crank.

The truth of this belief depends on your situation. Up to a point, cast cranks are fine. In a short-duration, normally aspirated bracket drag race engine, 450 genuine horsepower is around the upper limit for

A cast crank can be distinguished from a forged crank by its thinner parting line.

Notice the thicker parting line of this 350 forged crank. a small-block cast crank. Almost any true street-cruising application can get along just fine with a cast crank. At horsepower levels higher than 450, or if you are planning a nitrous or high-boost blower or turbo application, move to a forged steel crank.

Good used cast cranks are more numerous and less expensive than forged cranks. You can take the money you saved and spend it on something else. Just be sure the crank is magnafluxed and properly prepped and use a high-quality vibration damper (especially with a cast crank).

These days, a large number of forged cranks are available from aftermarket suppliers for a large range of applications, stroke lengths, steel alloys (most use a very strong 4340 alloy), and total weights. These aftermarket cranks can also be prepared in various ways. All of the counterweights can be knife-edged to reduce weight and windage. The crank pins on the rod journals can be drilled to further reduce weight. Extra-wide radius journal fillets add strength. Counterweights can be reduced in radius to reduce rotating mass. Special coatings are available that reduce oil cling, and chemical, vibration, and heat treatments are available that further harden and relieve the metals.

Crank Stroke and Journal Sizes

Crank strokes with small journals (2.30-inch mains/2.00-inch rods) include the 3.00-inch strokes on the Gen I 265, 283, and the 1967 302 Z28 engines. The 3.25-inch stroke lengths were used on 327s from 1962 through 1967 with small journals. The 5.7-inch rods with small rod journals and 11/32-inch rod bolts were used with these cranks.

Strokes with medium-size journals (2.45-inch mains/2.10-inch rods) include the 1968 to 1969 302 Z28 with a 3.00-inch stroke, a 3.10-inch stroke used on the 262, 3.25-inch used on the 307 and 1968 327s, and 3.48-inch strokes on the 267, 305, and 350. The Gen II 265-ci V-8 uses these journal sizes with a 3.0-inch stroke and one-piece rear main oil seal. The 5.7-inch rods with 2.10-inch rod journal sizes are used with these medium journal cranks with the exception of the Gen II 265 L99 motor, which uses a 5.940-inch rod. Production rods for medium-size journals have 3/8-inch rod bolts.

The 400 used a 3.75-inch stroke with larger main journal diameters of 2.65 inches and rod journals of 2.10 inches. The 400 uses a shorter 5.565-inch length rod with 3/8-inch rod bolts. These 400 rod bolts have a unique head on the bolt, which helped provide more clearance between the bolt head and cam lobes and the block itself.