Mopar Small-Blocks. Larry Shepard

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       The main bulkheads must have enough material and strength to support four-bolt caps with vertical outers. Thus, there must be enough material between the main cap bolt of the two-bolt design and the outer wall below the pan rail. In this drawing, the dotted line represents the standard block casting. The solid line above it is closer to the performance blocks, such as the 340 T/A and the X and R block families. The vertical outer bolts break through in the standard casting. The main reason for splayed outer bolts is to put the bolt into solid material. This drawing is not to scale.

      Most race blocks are bored or rough bored to approximately 4.00 inches. There are many reasons to use a race block even if the bore size is less than 4.00 inches (such as the 318’s 3.91 inches). If you plan to race a small-bore engine, such as 3.91 inches or even 3.63 inches, you should not use the production block. It is a better package to use the race block with the proper-size sleeves.

      Mains

      The two basic main sizes are the 273/318/340 and 5.2L engines. The 360 and 5.9L use a larger main. The 360 has a large 3.00-inch main; the other group is small at 2.69 inches. The main cap bolt spacing on the 360/5.9L is also wider, or spread. Magnum engines have a small dowel that locates the number-5 main cap. Magnums also use smaller main cap bolts in the number-5 cap. Typically the main caps are made of high-nickel cast iron. If the main caps have been replaced or damaged, or if they bind during crank rotation, the mains should be align-bored, which is a machine shop operation.

      Height

      Most A-engine blocks were built at 9.60-inch block height; Magnum engines were built at 9.58 inches. Race blocks can be about 9.00- to 9.10-inch block height. Do not try to mill a production block to this height. Deck milling on production blocks should be limited to about .060 inch.

      You need to determine if the engine was rebuilt or repaired in the past and whether the block was decked .060 inch at that time. If the block has been decked by .060, the actual deck now is 9.54 inches. You should not take off another .060 inch because the deck becomes too thin and causes head gasket sealing problems that you will not be able to fix. This is one reason that it is so important to measure the block’s actual height before you start machining.

      Stroke

      The A-engine/Magnum engine can generally accept long-stroke cranks. Most of them use a 3.31-inch stroke; the 360/5.9L uses a longer 3.58-inch stroke. The performance aftermarket offers 4.00-inch strokes that are easy fits. Because the camshaft sits so high above the crank, long-strokes do not cause the connecting rods to hit the camshaft lobes. The pan rail and the bottom of the cylinder bore (pulling the skirt too far out the bottom) are still concerns with strokes longer than 4.00 inches.

       Oil routes from the pump to the oil filter on the side of the block, and then back into the block and up to the right side (next to cylinders-2, -4, -6, and -8) main oil feed galley. The right oil galley runs from the rear of the engine to the front, and it feeds down to the main bearings. As can be seen, the tappets are oiled directly since the tappet bores intersect with the galley. Then the oil goes up to the cam bearings.

Block Oiling

      A-engine and Magnum blocks oil in basically the same way. The difference comes in oiling the head and valvetrain. The A-engine oils the valvetrain and head through the head; Magnum engines oil the valvetrain and head through the pushrods.

      Basically, the oil pump feeds the oil filter and then pushes oil to the passenger-side main oil galley. From the main oil galley, the oil feeds the passenger-side tappets and the main bearings. Then it crosses to the driver-side oil galley and oils the driver-side tappets. Then, from the mains, the oil goes to the camshaft bearing.

      On the A-engine, the oil goes to the rockers and the head from the cam bearing and through passages in the block and head to the rocker shaft. On Magnum engines, the oil goes to the head and rockers through the pushrods from each tappet.

      Block Plug Verification

      All A-engine and Magnum blocks have a special plug at the rear of the block pressed into a vertical passage in the block. The first priority is to check that it is there. The second priority is to see if it is properly installed because it is vital to the proper function of the oiling system.

       All small-blocks use a small, pressed-in plug at the rear of the block. This plug is not visible once it is installed. It is installed in a vertically drilled passage and divides the oil passages into “to-oil-filter” and “from-oil-filter” sections; both are drilled horizontally inward from the oil filter mounting area. This plug should sit at 7½ inches to 7 below the rear china wall and 2⅛ to 2⅜ inches above the parting line for the number-5 cap. If the plug is too low, use a flat dowel to tap upward into position.

       The special plug is very important to the engine’s oiling system. It blocks the oil from the oil pump from going straight up and forces it to go out to the oil filter. Once it passes through the filter it returns to the block above the plug and goes directly to the main oil galley. If the plug is missing or not installed properly, it could cause erratic, low, or no oil pressure.

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