Читать книгу Oldsmobile V-8 Engines - Bill Trovato - Страница 8
ОглавлениеOldsmobile engine blocks, as far as most Olds enthusiasts are concerned, started in 1965. The first V-8s in this new-style Oldsmobile engine line started as the 330-ci models for the small-block family and the 400- and 425-ci models for the big-block family. The engine-block designs remained virtually unchanged right up to the last Olds engine that came off the assembly line in the late 1980s. Olds blocks are very easy to identify. A letter cast into the front of the engine block under the intake manifold sealing rail identifies a small-block. A letter in the same place identifies a big-block.
Oldsmobile small-block V-8s consisted of a variety of cubic-inch models, including the 260-, 307-, 330-, 350-, and 403-ci engines. For high-performance use, the 350- and 403-ci versions are the most popular with Olds enthusiasts.
Oldsmobile small-blocks share many features. The bore spacing (defined as the center-to-center distance between the cylinders) was set at 4.625 inches, which is shared with the Olds big-block. The main bearing bores are set at 2.687 inches on all small-blocks with the exception of the diesels. The diesel block main-bearing bores are the same diameter as the big-block Olds, which are measured at 3.189 inches. The deck height, measured from the crankshaft centerline to the cylinder head mounting surface, is set at 9.330 inches on all small-block Oldsmobile V-8s. The lower portion of the block has only subtle differences, with the exception of the main-bearing webs. The lifter-valley areas in all the small-blocks are very similar and are not considered to be a weak spot. I have never seen a failure in this area. The lifter bores on all small-blocks are .842 inch in diameter and were all designed for use with flat-tappet hydraulic lifters. The exceptions are the later diesel blocks and late-model 307 gas engines, which had .921-inch-diameter lifter bores for use with hydraulic-roller lifters.
The Sunnen CK 10 cylinder hone does a great job of honing cylinders round and with little distortion. Newer, more advanced honing machines are available, but many top engine builders prefer this machine.
The letter at the end of the casting number indicates which big-block engine it is. An “A” casting is the 1965 425-ci engine, a “D” casting is the later 425-ci engine, a “G” casting is the long-stroke 400-ci engine, and an “F” casting is the 455 engine. Here, the little “A” next to the “F” means that this block has no provisions for a 4-speed.
The large numeral after the casting number indicates which small-block engine it is. A “2” is a 350-ci engine, a “4A” or “4B” is a 403-ci engine. Blocks with these numbers are about the only ones you want use for serious high-performance.
The main webbing on a gasoline small-block engine is even thinner than on the Olds big-block. How much stress can it handle? Who really knows? It depends on the weight of the rotating assembly, RPM, crank stiffness, detonation, static compression, and numerous other factors. Oldsmobile racers have pushed these blocks pretty far, but it’s only a matter of time before you run over the crankshaft when pushed to the limit.
As mentioned, the first of the Olds small-blocks was the 330-ci model, which was produced from 1965 to 1967. These engines have a 3.937-inch bore and a stroke of 3.385 inches. I have sonic tested a few of these blocks and you can safely overbore the cylinders .060 inch (or 4.000 inches) at best. The 330 blocks are, in my opinion, only good for restoration pieces. Although they appear to be as strong as any of the newer 350 blocks, the small bore size makes it an undesirable choice for high-performance use.
In 1968, the introduction of the 350-ci Olds engine stepped up the performance of the small-block by increasing the bore size to 4.057 inches. I have always wondered why Olds engineers chose such an oddball bore size. The 350 blocks share most of the features of the 330-ci block, with this notable exception. I have sonic tested some of the 1968–1974 blocks and have not found any whose cylinders couldn’t be safely overbored .060 inch. Most of the high-performance 350 engines that I build use a 4.125-inch bore with a custom-made piston. The 4.125-inch size is the best you can use to obtain the most horsepower in these engines. The cylinder wall thickness at this bore on these blocks is enough to allow the bore to remain round at all but the highest horsepower levels. I estimate that to be at 650 hp or less.
The main webs in this 403 block don’t have a whole lot of material to hold the crankshaft in the block. Some have had success in 12-second quarter-mile cars for a while, but I have seen them fail also. My opinion: Why go there? An engine failure is too costly. It’s too bad that Olds engineers lightened the structure; there would be an awful lot of these out there racing.
I have seen numerous performance Olds engines over the years and have yet to see a lifter bore failure. There is no need for modifications here.
In 1975, Oldsmobile introduced the 403-ci engine. This block shared a redesign with the 350 block to include a weight savings. One of these changes was the removal of the already thin main-bearing webs that tie into the main-bearing bores from the oil pan rails. Do not use one of these later-model 350 blocks for any high-performance build because the beefier pre-1975 blocks are still readily available.
The 403-ci small-block has the largest bore of any Olds engine, set at 4.350 inches. The cylinder walls are not that thick, however, and the best method of keeping a round bore is to keep the walls as thick as possible by honing the existing bore until it is perfectly straight and round, and then using a custom piston with file-to-fit rings. The maximum amount I would ever consider for an overbore on a 403 is .030-inch oversize. Forget any more than that. This block has siamesed cylinders that strengthen the area by tying the bores together side to side, but the rest of the cylinder thickness is borderline too thin due to the weight-saving redesign.
With the large-bore design, this block sounds like a great deal. Unfortunately, another way the Olds engineers saved weight in this block was by removing material and effectively adding windows to the already-weak main bearing webs. When looking at one of these blocks on the engine stand, it is plain to see that there is not much material to hold the spinning crank assembly in the block. You’d be lucky if the crankshaft doesn’t fall on the floor when you turn the engine stand over to bolt the heads on, let alone spin some RPM with rods and pistons connected! I’m exaggerating here, of course, but the main bearing webs are one of the important areas of strength in an engine block design. The Olds designers missed the boat on this one. There are, however, some alternatives.
One way of reducing some bottom-end stress with these engine blocks is to reduce the weight of the rotating and reciprocating lower-end components. Another way to help these engines is to use a main-bearing girdle (like the part made by J&S). It has been debated whether the girdle helps or doesn’t help, but I can say that the 403 engines that I have built with the girdle in place have not failed. The main-bearing girdle cannot weaken the lower end, so I put it on.
One particular 403 engine that I built for a customer has used the girdle and lightweight components with great success. This particular street-and-strip engine has aluminum connecting rods and lightweight custom pistons. The street-driven 1987 Cutlass in which the engine was installed ran 12.30-second passes at the quarter-mile drag strip (at full street weight and naturally aspirated) and 11.50-second times with a small amount of nitrous oxide. Yes, I said nitrous oxide. This 403-ci “bomb” is still ticking some four years later.
The Mondello engine-block girdle is a welded-together unit. I have seen numerous high-horsepower Oldsmobile engines perform reliably with it.
In 1977, the Oldsmobile Division decided to produce a diesel engine for the full-size Delta 88s. These Oldsmobile diesel engines were not necessarily good when new, and had a variety of warranty issues. However, it gave Olds racing enthusiasts a good block to convert into a bulletproof gasoline-powered high-performance engine.
Three versions of these blocks were available: the “D” casting block with .842-inch-diameter lifter bores, or the “DX” block with either .842-inch or .921-inch-diameter lifter bores. These blocks had the same deck height (9.330 inches) as all the gasoline Olds small-blocks. The main bearing bore used big-block dimensions (3.189 inches), which accepted a 3-inch main bearing journal big-block crankshaft, or the standard cast diesel crankshaft. The cylinder wall is much thicker than the gasoline small-blocks, and a diesel block’s cylinders can be bored to as much as 4.250-inch, although there are some parts of the bore that start getting thin at that size. Half-inch-diameter head bolts were used on these engines for improved head gasket sealing and will not have to be upgraded. The oiling system remains unchanged on these blocks.
The BTR girdle bolts are torqued to the pan rails with 3/8-inch grade-8 bolts. This ties the pan rail to the main caps and replaces the lack of sufficient thickness in the main webbing. It also ties together the three center caps and studs.
This four-bolt billet-steel main cap is designed for use in small-block diesel conversions. These caps are available for 2.5- and 3-inch main crankshafts. Generally, you only need the four-bolt caps for mains number-2, -3, and -4. One of the purposes of the four-bolt main cap is to keep the side of the block from spreading. I do not recommend four-bolt caps for thin main-web engines.
The injector-pump boss on a diesel block hits the timing chain unless it is cleared by grinding or some other method.
A neat little program on the Cincinnati CNC machine mills the injector pump area. It also mills a pocket in front of the number-1 cam bearing so that a capsulated thrust bearing can be installed to prevent wear between the camshaft and the cast-iron block. Not only does the thrust bearing prevent wear, it allows you to set the lifter-to-lobe relationship exactly where you want it.
To convert one of these engines for gasoline use, there are only a few minor modifications required. The diesel fuel-injector pump boss must be cleared, due to interference with standard timing chains. This task can be accomplished either by grinding the boss away by hand, machining it away on a mill, or (as I do) milling the area away on the CNC machine for maximum weight removal and the best-possible appearance. All above methods will get the job done.
The diesel timing chain cover may have to be changed to a standard-type gasoline engine piece; the seal area interferes with some harmonic balancers. Additionally, if a back-grooved cam bearing is to be used, the passage that connects the top of the cam bearing bore to the injector pump hole must be plugged with a .250-inch-diameter dowel. The length of the dowel is unimportant as long as it seals the passage and doesn’t move. I’ve found that 1/2- to 3/4-inch lengths are fine. Chances are you will be making a dowel on the lathe out of a piece of aluminum that will fit the hole exactly, as this is a drilled hole and is not necessarily a precise diameter. This dowel plug has a .001-inch or so press-fit clearance, and is installed in the passage with the cam bearing removed. The dowel is typically driven into position with a long drift punch through the connecting passage in the number-1 cam-bearing oil-feed hole. If a conventional (non-back-grooved) cam bearing is to be utilized, this passage can remain open, because the cam-bearing shell seals the hole.
Small-block diesel engines are relatively easy to spot. They have a “-D3” code on the block behind the timing cover, along with a rather large “D” or “DX” on the side of the block near the freeze plug area.
Oldsmobile also made a special high-performance engine block commonly referred to as the “NASCAR block.” These high-performance blocks can still be found, but are very rare. There are many different variations of these, but there are basically two different models. One carries Olds PN 22528096 and features coolant-flow passages between the cylinders. The other carries Olds PN 22527735 and has siamesed cylinder bores, which have no coolant-flow passages between the cylinders and allow for larger bore diameters. The siamesed NASCAR blocks can handle bore sizes as large as 4.350 and still retain ample cylinder-wall thickness. The only concern at that point is the lack of space between the cylinders; this is where head gaskets are challenged to seal, as horsepower and cylinder pressure get higher.
The pocket that is cut into the camshaft thrust area is cut precisely so that the thrust bearing stays in place. Because approximately .140 inch is machined out of the block to retain the thrust bearing, the cam bearing needs to be driven into the block by that amount minus about .030 inch.
This late 39-degree 425 block used .921-inch lifter bores and had bronze lifter bore bushings installed that were finish machined to .842 diameter for use with more readily available parts.
The endmill machines a pocket that is 2.930 × .140 inches deep to allow the Cloyes roller thrust bearing to sit in the pocket without falling out. This DX block has main-bearing spacers. It is best to use a main cap that is the proper size so that the only spacer needed is in the block.
The timing cover on the left is the stock version found on every gasoline-powered Oldsmobile engine. The timing cover on the right is from a diesel engine. The harmonic-balancer seal protrudes from the front of the timing cover. It is best to check for interference before you glue this cover on. This hits some harmonic balancers, and does not hit others.
The siamesed-cylinder NASCAR blocks are the rarest, strongest, and most desirable of these high-performance castings. I have seen many of the special high-performance Olds blocks and there seems to be so many variations and inconsistencies, so it isn’t worth discussing them all. I have seen the PN 22528096 “non-siamesed” block have siamesed cylinders. I have seen blocks with 2.500-, 2.750-, and 3.000-inch main-bearing diameters. I have seen each of these blocks with .842-, .875-, and .921-inch-diameter lifter bores, etc. The only way to determine if the block has siamesed cylinder bores is to visually inspect them through the freeze-plug holes. Each block, regardless of part number, must be visually inspected to see exactly what features and dimensions it truly has.
Oldsmobile big-block engines also consisted of three different cubic-inch displacements. They were offered at 400, 425, and 455 ci. With regard to high-performance use, the 455 is the most popular and is used most by Olds enthusiasts.
Oldsmobile big-blocks have many shared features and dimensions. The bore spacing between the cylinders is the same as all Olds engines at 4.625 inches. The main-housing bores are all set at 3.189 inches on all big-block engines. The deck height (measured from the crankshaft centerline to the cylinder-head mounting surface) is set at 10.625 inches on all of the big Oldsmobile blocks. Most of the factory blocks measure right on that dimension too. The lifter-valley areas in all the big-blocks are very similar and are not considered to be a weak spot. I have never seen a failure in this area. The lifter bores on the 400/425 engines could be .842 or .921 diameter, depending on the application. The 455 engines all retained the .842-diameter lifter bores, and all were designed for hydraulic flat-tappet lifters. The main webs are quite thin and are virtually the same on all models. Forget about four-bolt main-bearing caps; there is nothing to bolt to.
This number designates a siamesed NASCAR block.
Older 1968–1970 model-year engine blocks had a casting designation at the rear of the engine, near the bellhousing area, of 68F, F1, F2, or F3. It has been circulated that these blocks had higher nickel content, and are therefore more desirable. I consider this to be a myth. I have honed many blocks with high nickel content, and soft honing stones are always required to finish high-nickel content blocks. But I have never had to use a soft stone on an Olds block. I have never found much of a difference at all between later-model and earlier-model blocks. I have also sonic tested many Oldsmobile big-blocks and actually found some later blocks to have thicker cylinder walls than some older models. Some of the thickest cylinder walls I have seen on 455 blocks are the later F6 blocks. It’s easy to see if you look through the water jacket holes in the deck at the backside of the cylinders. If you look at one of these blocks next to any of the others, it’s easy to see the difference.
The main webs are considerably thicker on this NASCAR block, compared to a production diesel block. Other than the main bearing bore diameter, the bottom side of the blocks is the same.
With all that being stated, the best way to select a good Oldsmobile big-block core is to simply look over the entire casting. This includes inspecting inside the water jackets from the deck and freeze-plug area. Some blocks have thicker walls than others, and this can typically be seen by the naked eye. A block that has had antifreeze in it all its usable life ultimately has thicker cylinder walls, due to less deterioration from rust. Rust is most common on cooling systems serviced with water alone. The thinnest spots in the cylinder walls are in the area between the cylinders. Sonic testing, or measuring the space between the cylinder walls through the freeze-plug holes, can determine this thickness.
NASCAR blocks (shown) are essentially the same in the lifter valley as diesel blocks, other than the lack of the injector-pump boss.
If you know the amount of space between the cylinders, you can determine the approximate cylinder wall thickness at that point by subtracting the distance between the cylinder walls from the bore-spacing dimension (4.625 inches) and dividing by 2. The average big-block can be bored safely to 4.185 inches and maintain round cylinders with as much power as the block can handle. A 4.200-inch bore can work well on a good core with about 600 hp. Some builders go to 4.250-inch bore, but this leaves the cylinder wall thickness about .090-inch thick at the thinnest area. I do not recommend this. Good piston-ring seal and oil control far outweigh the small cubic-inch and potential cylinder-head flow gain the bigger bore brings with it.
The main webs on big-block Olds engines are very thin and need some sort of a girdle instead.
The latest long-stroke 400 G block can be bored and honed to 4.000 inches safely in limited horsepower applications. This bore generally leaves about .250-inch wall thickness everywhere at that size, which is acceptable in the 400- to 500-hp range, which is all you would ever ask for in one of these situations anyway.
I have half-filled Olds blocks with cement-type products (HardBlock or similar) that occupy the water jackets for the purpose of tying in the cylinder walls for strength. I have not found that it helps ring seal significantly; I don’t use it unless the customer requests it specifically. The negative effect of block filling is that there is less cooling of the crankcase oil, which can cause high oil temperatures while driving on the street or when making back-to-back passes during round-robin bracket racing.
I call this the poor man’s sonic test. The thinnest parts of the cylinder walls are in the 9-o’clock and 3-o’clock position as you are facing the block decks. So if you measure the space between the cylinders and subtract the bore spacing (4.625 inches) and divide by 2, you get the approximate cylinder wall thickness in the thinnest areas.
A typical cylinder wall thickness for a 4.185-inch-bore big-block in the 9-o’clock position is about .200 inch. This one is on the thick side.
This same “D” 425 block sonic tested in the 3-o’clock position is still plenty thick to hold a round bore.
Cylinder-wall thickness in the 6-o’clock and 12-o’clock positions is almost not even worth checking. I have always found them to be very thick.
If you must half-fill your Oldsmobile block, make sure that the fill is not so high that the water cannot transfer from cylinder to cylinder. Generally, if you fill to the bottom of the water pump holes, it is too high. Look through the water holes in the deck and plan the amount of fill before you pour. If your block is already filled to the base of the water pump holes, look through the deck at the water passages to verify that water is able to transfer from cylinder to cylinder. If the water cannot transfer, the only way to fix it is to fabricate an external manifold, or use a combination of pipe fittings and hoses to return or feed the water from each cylinder.
My 1,250-hp nitrous, siamese NASCAR small-block build is all-out max-effort build. I have completely filled the block; I use no water for cooling. I have found that this method seems to hold the cylinder walls in shape even with the abuse of detonation and burning pistons. This technique is good for builds such as mine but is also good for any Oldsmobile engine block. However, you have to pay attention to the way you race with this type of block and how much heat you put into the engine prior to the run. Forget bracket racing in round-robin situations; I don’t recommend it.
There are two lifter-bank angles in the Oldsmobile engine, commonly referred to as the 39-degree and the 45-degree blocks. The older 400- and 425-ci engines could be either, depending on their production year and model. All 330-ci Olds engines have a 45-degree bank angle, and all 1968-and-newer Olds engines have the 39-degree bank. What most people don’t know is that the actual bank angle on the 39-degree block is 42 degrees, meaning that the lifters are actually 42 degrees apart from each other.
The easiest way to determine which block you have is to install something (like a straight edge) into the lifter bore and determine if it is parallel to the cylinder wall or not. The cylinder bores are cast at a 45-degree angle, so if the lifter bores align with them, you have a 45-degree block. It should be plain to see one way or the other.
The camshaft cores are sometimes more difficult to find (and may be more expensive) for the 45-degree block. If you have a choice, the 39-degree block is more desirable. I have found that the 45-degree blocks cannot be converted to a 39-degree (42-degree) bank angle by boring and bushing due to the lack of sufficient material in the lifter-bore bosses. I did try.
The days of “hot tanking” a block are gone. Heating a large vat of some form of acid is just not feasible in business, due to cost and toxicity. As far as I’m concerned, the only proper way to clean cast-iron engine blocks is to use the bake/blast/wash process. In this process, the block is stripped of all the plug and cam bearings, placed in an oven, and baked at 700 degrees F for two to three hours. Whatever oil, grease, and dirt that is on the block or hiding in oil passages is turned to ash.
The next step is to place the block in the blast machine. The block is fastened inside a rotating fixture and steel shot is thrown around by a high-speed paddle wheel. The ash and rust is completely removed in about 10 minutes of run time. Jet washing with hot soapy water after that removes the rust residue and leftover shot. The engine block looks brand new at this point and the machining process can begin.
The first machining operation to do on the engine block is the main bearing bore work. If the block is machined properly, most of the block-machining operations were referenced off the main bearing bores. You can check main bearing bore size by torquing the main caps and measuring roundness and diameter by using a dial bore gauge. It is not quite as easy to check for alignment. Some old-school books show the use of a straightedge and feeler gauges, but I consider this method to be a waste of time. I have set some factory blocks on a mill and indicated the end main journals until they read zero on each, and run the indicator along the center three mains and found some to be within a few tenths, and some to be off by .002!
Some people wonder why they wipe out main bearings with a .0025 main bearing clearance. If you want to avoid a future headache, just have the mains align honed and be done with it. This process is one that requires some skill and experience; be sure to select the right shop to do the job. I have seen many blocks that were line honed and were far from “aligned.” If you are installing aftermarket caps, the block must be align bored and align honed anyway, so you are good to go.
Boring the cylinders is simply a method of sizing the cylinders for an oversize piston. The cylinders at my shop are bored .005 to .008 under final size. Some literature specifies that you can bore within .003 and then final hone, but depending on the finish after the boring operation, that amount may not be enough to remove tooling marks. It takes more time in the hone, but you are guaranteed the proper finish with the extra material. Engine blocks at my shop are bored on a very large Cincinnati CNC machine. A precision bar goes through the main journals and cam tunnel. When the block is set on the machine fixture, each bore is machined exactly 45 degrees from main/camshaft centerline, and parallel to them. The bore locations are referenced off the cylinder-head dowel pins, and bore spacing is set at 4.625 inches in the boring program. This ensures that all of the machine work of the block is “blueprinted.”
The blasting unit houses the previously thermal-cleaned, completely dry engine blocks or cylinder heads. They are fastened inside and rotate 360 degrees while a high-speed paddlewheel throws steel shot at the parts. Five minutes later, a previously rusty engine block looks like brand new and is ready for machining.
Block Decking
The next block machining operation is to deck the block for the purpose of making the surface flat for head-gasket sealing and machining a predetermined deck height. Deck height is referred to as the distance from the crankshaft centerline to the cylinder-head gasket surface of the engine block. I make the surface absolutely smooth and am convinced that a smooth surface seals the best on any gasket. Rough finishes to “bite” the gasket simply leave peaks and valleys. I’m sorry, but I don’t want any valleys in a sealing surface. The deck surfaces are cut immediately after the boring operation without the block being moved from the fixture; therefore, the deck surface has to be perpendicular to the bores and parallel to the main journals. The cutter is referenced (or zeroed) from the main-journal centerline. And if a deck height of 10.600 inches is desired, then the cutter is raised to 10.600 inches and the deck is cut.
A thermal cleaning oven does a great job of cleaning all of the oil and grease from an engine block, cylinder heads, or parts. It is not a good idea to thermal clean aluminum heads or parts. The amount of heat required to clean properly affects the heat treatment of the part and can soften it considerably.
Honing
The honing process is one that seems to attract many different opinions on how it should be performed. I have tried many procedures and found that they all seem to work about the same as long as the cylinder is straight and round. Some finishes seem to help on different tension rings but, in general, I wouldn’t worry about the different finishes that some engine builders prefer to create. I also stress that you can’t get the bores too straight or too round. This is the single most important part of the honing process. When I hone cylinders, I install a 2-inch-thick torque plate. I have not found different results between a steel torque plate and an aluminum plate. I simply use the aluminum plate for everything.
At BTR the block is set up on a precision fixture that holds it at 45 degrees to engine centerline. The block is bored and decked in one operation; therefore, the decks have to be parallel to the mains and perpendicular to the bores. With the cutter referencing off the precision main bar, deck heights can be cut very easily to any desired dimension.
Blueprint specifications for small- and big-block Oldsmobile engines.
I use a 150-grit stone and bring the bore to .0025 to .003 inch of the final dimension. A 220-grit stone can be used to finish also, but the 150-grit stone simply reduces honing time and heat. I hone .0003 inch under the final dimension with the 220-grit stone. The final step is to give each cylinder three up-and-down strokes with a 280-grit stone; the same with the 400-grit stone.
The Sunnen CK 10-cylinder hone does a great job of honing cylinders round and with little distortion. Newer, more advanced honing machines are available, but many top engine builders prefer this machine.
There are disagreements about whether diamond stones should or shouldn’t be used for performance applications. My feeling is that the stone is the better process, because as the stone wears, you get fresh stone to cut with. The diamond really doesn’t wear away much, which leaves a rounded grit over time. I can’t say it is wrong to use the diamond abrasives; it’s just my preference to use the stones and it works for me.
Camshaft Thrust Surface
All Olds blocks have the same thrust-pad dimensions, with the notable exception of diesel blocks. The thrust pad for these blocks is .050 inch deeper than for gas blocks. Less material is machined on that thrust surface to maintain proper lifter-to-cam lobe relationship when using a conventional non-diesel Oldsmobile camshaft. A common procedure that I use is to machine the camshaft thrust surface into the front of the block for a roller thrust bearing, otherwise known as a Torrington bearing. Over the years, I have seen many blocks scored in this area.
The reverse rotation of the distributor gear forces the camshaft against the block and can sometimes wear in this area. The ultimate solution is to machine a pocket into the block that allows a one-piece thrust bearing to fit snugly into the front of the block, so that the camshaft rides on that roller surface and cannot wear. The bearing to use is the Cloyes PN 9-220 roller thrust bearing, and the pocket needs to be machined 2.930 inches around and .140 inch deep for the bearing to fit properly. The .140-inch depth is critical, mostly because of the lobe-to-lifter relationship.
On a roller-cam application the lifter should be in the center of the camshaft lobe. It is critical to have the lifter positioned correctly when the cam and lifter are the flat-tappet type of design to ensure rotation of the lifter during operation. The centerline of the camshaft lobe should be offset .060 inch to the rear of the block from the centerline of the lifter. By machining the thrust pocket to the same depth as the thickness of the bearing, that stock relationship is maintained. The front cam bearing needs to be installed farther rearward to prevent contact with the roller bearing. It can extend slightly into that pocket without hitting the inner race of the bearing. When the front cam bearing is installed, the oil hole (or groove) is blocked slightly and does not create an issue.
You must also consider the upper and lower timing gear relationship and distributor gear and camshaft gear relationship when adding these thrust washers or thrust bearings. Many novice Oldsmobile engine builders take shortcuts and add only the bearing or bronze thrust washer behind the camshaft to move it forward. When the camshaft is moved forward by this method, the two gears do not mesh properly and can wear prematurely. If you maintain the OEM thrust surface location with proper machining, you should have no issues.
Thrust Washers
Competition Cams manufactures a .041-inch-thick bronze thrust washer (PN 225) that protects the engine’s camshaft thrust surface when it is not feasible to machine your block for a roller thrust bearing. You do, however, need to machine that thrust washer thickness off the thrust face of the camshaft to provide the proper alignment between the timing chain set and the distributor gear to maintain the proper lifter-to-lobe relationship. I do not recommend installing bronze thrust washers without machining the block or camshaft. This is especially critical with flat-tappet camshafts. Proper lifter rotation does not occur if the .060 lifter-to-lobe offset is not maintained.
This .041-inch-thick bronze spacer is available through many Oldsmobile vendor sources and from Comp Cams. It is always a good idea to use a thrust bearing or thrust washer to protect the front of the block from wearing.
Head Bolts
I convert from the factory 7/16-inch-diameter head bolts to 1/2-inch-diameter head bolts (or studs) whenever the customer allows. There is plenty of material in the block to do so, and this adds valuable clamping force to the 10-head bolt design, which makes this modification a no-brainer. Drilling by hand is not generally acceptable unless you’ve made a tool to keep the drill perfectly square to the deck. To do it yourself, you could make a tool that bolts to the deck of the block and allows you to drill and tap the hole absolutely straight. As long as the hole is on location and is perpendicular to the deck, it doesn’t matter if you use a hammer and a chisel to do the job. I prefer to do the job on the precision CNC milling machine, though.
Big-block Oldsmobile engine blocks are generally pretty reliable for engines making between 600 and 650 hp. After that, you should consider a bottom-end girdle. I have seen many block failures, and with a little Internet research you can find many Olds engine-block failure photos that can help you draw some of your own conclusions. Olds experts agree that the most common failures occur at the number-4 main-web areas. The use of solid motor mounts, which are fastened to the block in this area, is the leading cause for failure. All of the engine’s torque and vehicle weight is transmitted in this motor-mount area via two 7/16-inch-diameter bolts.
The use of front-mounted motor plates and rubber mounts with engine torque limiters should help. The main reason for the failure is the design of the block. There is simply not enough material in critical areas to hold the crankshaft in place and resist block flexing. A number of girdles from different manufacturers can stiffen the block. Some of these girdle manufacturers made them at one time and do not make them anymore, some have them in stock, and some are made only to order.
These girdles all have a slightly different design. These main girdles have been available through such companies as Mondello Performance, Product Engineering, J&S Machine, Rocket Racing, Product Engineering, Dick Miller Racing, Jeff Smith Racing, and Noel Engineering. The goal of these girdles is to reduce block flex and keep the oil-pan rails from spreading due to the thin main webs.
The first type of girdle, the “halo” girdle, is available through both Dick Miller Racing and J&S Machine and bolts onto the block with very little (if any) modifications to block or oil pan, unlike the so-called pan rail-type girdles. It bolts on top of the numbers-1 to -4 main caps and ties them together. Most 403-ci-engine enthusiasts use this style of girdle for ease of installation and cost. I have seen many 403 engines destroyed due to block breakage, but fewer if the halo girdle had been installed on them. I consider this modification cheap insurance for these engines.
To determine if an engine block has siamesed cylinders, look through the freeze plug holes to see if the cylinders are connected. A standard non-siamesed block has a space between the cylinders to allow coolant to pass through.
The Program Engineering girdle (shown) uses steel inner caps, but my preference is the stock caps with a billet girdle surrounding the three main caps and tying everything together.
The Noel Engineering girdle is the strongest girdle made for an Oldsmobile engine. Notice the keyed main caps. Once this whole thing is bolted together, the block and the caps cannot move in any direction. The quality of these girdles is impeccable. Quite a bit of time is involved in making them and they are not cheap, but if you want the best, this is it.
The Noel Engineering girdle has cross-bolted mains, and the 3/4-inch-thick girdle pan rails are torqued to the engine-block pan rails with a nut and stud in every bolt hole. These are the strongest of all the girdles, but unfortunately, there were only a few made, due to the expense in small-run manufacturing.
Jeff Smith made only a few girdles, but the design worked well and is a proven piece.
This is the beginning stage of the BTR one-piece billet engine-block girdle. It starts out as a 150-pound piece of steel; when finished it weighs a mere 18 pounds.
The second category of block girdle is a one-piece unit, either manufactured from a single piece of billet or a series of welded-together parts to make it a one-piece unit. This girdle bolts to the oil pan rails of the block and the girdle material ties the two rails together by crossing over the main caps and tying everything together. Many 800- to 900-hp Olds engines have successfully used this style of girdle. These have been made through Jeff Smith Racing, BTR Performance, Rocket Racing, and Mondello Performance.
The third category of girdle is a bolt-together design that is available through Product Engineering and sometimes available through Noel Engineering. The Product Engineering girdle kit comes supplied with steel main caps for numbers-1 to -4, pan rails, and fasteners. The pan rails bolt in place and bolt into the -1 to -4 main caps through the side. The girdle sold by Noel Engineering is a little more sophisticated. It is installed in the same manner, but the supplied main caps are tightly keyed and bolted to the pan rail sections. I think this is the strongest unit made. The main caps cannot walk or move because they are keyed vertically and bolted. This is an extremely high-quality unit, and in my opinion is the most desirable.
The bad news is there were only a few made and no more will be made unless enough orders are taken for a higher production run. Keep in mind that the pan-rail girdles are considered the strongest of the breed, but require oil-pan modifications. Aluminum oil pans made by Moroso are available for the BTR Performance, Product Engineering, Jeff Smith, and Mondello girdles through me at BTR Performance.
The finished BTR engine-block girdle is one of the few Oldsmobile girdles that are often kept in stock. This style of girdle is a proven piece, and I have seen it help hold together engines making about 900 hp on big-block Oldsmobile engines.
In general, it is best to use the 1968–1976 Olds blocks for most high-performance applications up to about 650 hp. If your engine-project goal is above that level, choose a gasoline block with an aftermarket girdle or use a 350 D or DX block with a four-bolt main-bearing-cap conversion for your high-performance project. You could try to find a suitable NASCAR block. They are out there if you are willing to pay the high price for them.
BTR girdle bolts are torqued to the pan rails with 3/8-inch Grade-8 bolts. This ties the pan rail to the main caps and replaces the lack of sufficient thickness in the main webbing. It also ties together the three center caps and studs.
