Racing Engine Block Prep - The Foundation

If you have your freeze plugs in place, it's also a good idea to pressure test the block before beginning the big projects. Pressure testing is done by filling the water jackets and then adding air pressure to see if there are any cracks or leaks. Both of these processes should be repeated after all the machine work is done to make sure you didn't cut too much away. Many machinists say they have seen situations in which a chunk of casting slag that was knocked away during one of the cutting procedures opens a pinhole through to a water jacket. The only way to catch this is with a final pressure check before engine assembly begins.

Align-Hone the Main Bores Align-honing the main bores for the crank journals should be the first machining operation performed because every other machining operation should ideally be referenced off of the crank centerline. Since the crank isn't in the block, this point is determined by the housing bore. When this is done, the caps must be properly fitted to the block and torqued into place. It is also a good idea to have an old oil pump housing bolted into place to simulate the distortion created.

The process of align-honing the main bores ensures that the bore housing inside diameters are correct and that all the holes are perfectly aligned to eliminate excessive bearing wear on any high or low spots. A good machinist spins the block 180 degrees during the process and runs the hone through the bores in the opposite direction for a few passes. This ensures that all the bores are identical and there is no droop caused by the boring bar. Usually, this procedure costs $225.

Boring and Honing Boring is the process of cutting away metal with a carbide cutting tool. Honing is much the same except a stone is used and you deal with much smaller increments.

Boring and honing isn't just about punching out the cylinder bores to a larger size. You have to make sure each cylinder is perfectly round and straight (perpendicular to the centerline of the crank). When boring the block, the machinist should use a fixture that locates the block on the crank saddles and another that locates the proper place for each cylinder (commonly a B-H-J Bor-Tru plate). This can help fix cylinder bore misalignment from the factory. Typically, the bores will be bored within approximately 0.005 or 0.006 inch of the final diameter.

The last bit of material is left on purpose to be removed by the honing process. Honing a bore, when properly done, leaves a fine crosshatch of valleys in which oil collects. A perfectly smooth cylinder wall wears rings very quickly. For racing, make sure your machinist attaches a torque plate before honing. A torque plate simulates the stretch caused by torquing a cylinder head in place. Also, you must use a head gasket between the block and torque plate to properly simulate the stress caused by a cylinder head. The head gasket should be the same type used on the final build. Guild says he has seen variances caused by honing with a standard composition head gasket and then building the engine with an MLS (multilayer steel) gasket. Usually, honing is done with a series of progressively finer stones (usually three) and takes some time. That's why the boring and honing process on the cylinders can cost $300 or more.

On a rebuild, if the engine has not been damaged, you can often get by with a light re-hone that removes as little as 0.0005 inch. This is enough to etch the cylinder walls, but removes so little that you don't have to go up a piston size.

Decking the Block Decking is the process of cutting down the portion of the block to which the cylinder heads mate. This is important for several reasons. First, it is often necessary to remove some material from this part of the block just to "square up" the cylinder heads. The deck of the block must be perpendicular to the crankshaft centerline. In a V-8, the decks on both sides of the block are at 90-degree angles to each other. A block should also be decked to ensure a good, flat surface so that you can achieve a good gasket seal.

Finally, a block must often be decked to achieve the proper deck height. Deck height is the distance from the crank centerline to the deck surface. Normally, the deck height is established just a few thousandths above the piston top when it is at TDC. Manipulating the block's deck height helps dial-in compression and also ensures the proper quench area. Quench is when the piston comes within around 0.060 to 0.045 inch of the deck of the head (this includes the thickness of the gasket). Proper quench area promotes good mixture motion of the air/fuel charge and more efficient combustion. Whenever you make a change in deck height, you must also make sure that there is still sufficient piston-to-valve clearance. Ken Troutman of KT Engine Development says decking a new block usually costs around $175.