Mopar Small-Blocks. Larry Shepard
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which was the best of both worlds. Then Mopar Performance introduced the six-bolt block (versus the standard four-bolt block) and the problems have disappeared. Note: Four or six bolts around each cylinder.
If you want to use an O-ring, however, they are generally used with copper head gaskets. You use a .032-inch-thick stainless steel wire. The machine shop must cut a groove around each bore that is .032-inch wide and .017-inch deep. The round wire sticks above the deck surface and with the proper gasket (copper), they work very well. In practice, it is more common to O-ring the cylinder head (rather than the block). Do not O-ring both.
On used blocks, you need to replace the pressed-in distributor bushing. On a new block, check that it has a bushing pressed in properly. It is poorly oiled and takes a lot of abuse in performance applications so it is best to replace it in any used block. If it is worn, it affects the ignition timing and allows the camshaft a walk. This movement changes the cam events that you try so hard to control.
You can use the intermediate shaft and gear to test the distributor bushing. Lower the gear into position just above the cam where the gear is not engaged. This position is about 1 to 1.5 inches raised above the gear’s seated position. Try to wiggle the shaft in different directions.
You can also practice the gear install. To lower the shaft and gear into position, the gear rotates. The slot in the gear is supposed to be pointing at the first intake-attaching bolt on the driver’s side once it gets into position. This takes some practice to get this to occur.
Generally, the last step in the engine disassembly process is to spin the crank once the rod-and-piston assemblies are removed. The engine builder tends to notice a tight spot during the general disassembly, but the final spin is confirmation. If no tight spot is observed during the disassembly process, the align-boring operation is not required. It is required if the block has been welded upon or suffered a major failure.
Sonic Testing
Sonic testing uses sound waves to determine the cylinder wall thickness around the bore. Thus it tells you how thick the bores actually are and if there is any core shift, and if there is core shirt, which direction it is in. If you are building many engines, buy a high-quality sonic tester; otherwise have your machine shop sonically test the block. The major thrust area on the driver’s side of each bank should be tested.
By determining bore thickness, you can figure out how much overbore is safe and where to stop. If you have two or more blocks, it tells you which one is best. Always sonic test before you start the overboring process. If a cylinder is found to be too thin, re-sleeve the cylinder or use a different block.
Sleeving
You can use sleeving as a repair or as a bore change.
Once the block is cleaned, the machine shop may tell you that one or two of the block’s cylinder bores are damaged and need to be fixed. Basic wear and/or scoring in the bore are the most common causes. No matter the reason, sleeving by a machine shop should fix it. If the process is executed properly, the rebuilt engine should be as good as new.
There are no 318 race blocks and the smallest 340/360 race block bore is 4.00 inches. The 318 block cannot be bored out to a 4.00-inch bore (3.97 inches on pre-1973 blocks but only 3.94–3.95 on 1973 and newer thinwall cast blocks). Perhaps your current race engine is worn-out; its last rebuild was at the maximum bore size for this block and it is time for another rebuild. Do you scrap the block? Sleeving all eight cylinders is one solution.
As the open loads went past 500 pounds, the friction went up and the racers wanted to use 50-mm roller cam bearings. With the 50-mm roller cam bearing, all the bearings are the same size and the inside diameter of the bearing itself is about the same, but the roller bearing is larger in outside diameter and this means the block must be machined for bigger bearing diameters. Most stock production blocks do not have enough material in this area to allow this to occur. This feature was added to all R-blocks. (Photo Courtesy R. Koffel)
The production main caps are cast all together and then cut apart. They are rough machined and then installed onto the block for final machining. The number-5 cap (on right) is the most obvious. The other four caps look very similar.
The number-3 cap takes the crank’s thrust, so it is machined differently than the -1, -2, and -4 caps. The number-3 cap on the left has the front and rear faces machined to accept the flanged thrust bearing. On the number-1, -2, and -4 caps (cap on right), there is no relief for the thrust bearing flanges.
The number-5 cap is the most complicated. The rear oil pan seal installs across the top at the bottom. The crank flange is below this surface and not part of the cap. The main cap bolts are toward the top left and middle right. The oil pump bolts to the two threaded holes (center top and middle left) and the oil passes through the hole between these two attaching holes.
The first step in building up a short block is to install the main bearings. Actually, you install the upper shell, which has the oil hole in the center and the groove around the face from side to side. It is very important that each oil hole line up with the hole in the block. The groove helps spread the oil and oil pressure around the crank journal. The other shell goes in the cap itself and does not have the hole and usually does not have the groove.
What if you want a race block with a bore of 3.97 inches (a .060-inch 318)? For small bores or worn bores, sleeving is a reasonable approach. For example, if you want to build a 310-ci A-engine with the readily available 3.31-inch stroker based on the 360/5.9L block (original 4.00-inch bores), you need a 3.86-inch bore. Sleeving is the only way to accomplish this bore size.
The typical main cap is made of cast iron (high-nickel alloy), similar to the block. Most race blocks use four-bolt caps, which may be steel or ductile iron. The number-3 cap is specially machined to accept the thrust bearing on the front and rear faces. The most complicated cap is the number-5.
Heavy-Duty Main Caps
All production blocks have cast-iron main caps with a tensile strength of approximately 241,000 psi. The tensile strength of ductile cast iron is about 413,000 psi, or more than 70 percent higher. Making main caps out of ductile cast iron results in a big strength gain. Most R-family race blocks use special upgraded heavy-duty caps (ductile iron or steel). Also, the 360 and 5.9L engines, which have the larger main diameters, should also have the main cap bolts spread .31 inch farther apart than other engines.
The tricky part with the mains caps is that they must stay in order: number-1 cap on the number-1 main bulkhead, etc. Cap numbers-3 and -5 are easy, but the other three all look alike. The production engineers had the caps’ number cast into the top of the cap, 1, 2, etc. Since the mid-1980s, the caps have two numbers on them: one for the V-8 version and one for the V-6 version (“4” on V-4s and “3” on V-6s). Without cast numbers, you would have to stamp the main number onto the cap once installed. The cast numbers on the