7. A fresh, correctly machined...
7. A fresh, correctly machined block should be the basis for every engine build. When choosing pistons, you’ll need to account for the piston depth in the block, as it affects compression ratio and piston-to-valve clearance, among other things.
When you use studs, the whole length of the threaded portion in the block is used. This could slightly distort the block, which in turn distorts the main journals themselves. This is also the case when main cap girdles are installed. Even when not using studs or girdles, it's a good idea to have your block's mains checked for straightness. A discrepancy here could throw out main bearing clearances or cause some unnecessary rotating drag on your crankshaft.
Square Decking: There is a difference between decking a block and square decking a block. When you deck a block, you basically remove some material to make sure the deck is flat and straight. When you square deck a block, you ensure that the deck surfaces are equally parallel to the crankshaft centerline. When this is accomplished, then each piston should nominally come up to the same deck height on each cylinder. If this is not accomplished, then you may find that your block can be up to 0.015- to 0.020-inch tall/short depending on the particular cylinder. How good would it be to have one piston at zero deck height and another piston 0.010-inch down in the hole?
As an added note here, when you square deck a block, you can specify where you want the pistons to be in relation to the deck. As my own general rule, I try to get the pistons around 0.005-inch below deck up to zero deck (where the pistons are basically flush with the deck surface). With a 0.040-inch gasket thickness, this will give a 0.040- to 0.045-inch quench distance. Any quality machine shop will have a fixture that will allow it to machine the block to this spec.
How do you determine what deck height you will need? Add your rod length, half your stroke, and your piston compression height together. Take, for example, a 347ci small-block. This is a pretty common combination and in this case we have:
5.400-inch rod length + (3.400-inch stroke/2) + 1.090-inch compression height = 8.190 inches
If we wanted the pistons to sit approximately 0.005-inch in the hole, then we would need a 8.195-inch deck height on the block.
You've probably already picked up on the fact that before you have your machine work done, you need to know (or have a really good idea on) which rotating assembly parts you're going to use.
Quality machine work is imperative for a quality engine build. Sure, you may be able to get away with running a brush hone through the cylinders, knocking some new cam bearings in, shooting some rattle-can paint at it and calling it a day. However, the more detail you place here, the more you will be rewarded; not only in assembly, but also in performance. This is the foundation and basis for the entire engine build. Money spent here is very well spent.
For the next installment of Power Principles, we'll concentrate on picking out cylinder heads, camshafts, and intake. The engine block is the foundation, but a well-designed and well-built engine relies on a clear, concise plan of attack, and a well-matched set of induction components that can move the air and fuel as efficiently as possible into and out of the cylinders.
8. A dial indicator, in combination...
8. A dial indicator, in combination with a straight edge and feeler gauge, can be used to see how far below (or above) deck the pistons are. This is an important dimension to have for your compression ratio calculations.
9. The forces that the reciprocating...
9. The forces that the reciprocating assembly can exert on the block can sometimes overwhelm the main bearing caps and the fasteners that hold them in place. Under heavy loads, the caps can shift or “walk” from side to side. This movement can then cause the threads of the fasteners to become fatigued. Eventually, the main web cracks, leading to a loss in oil pressure and possibly catastrophic damage to the block and rotating assembly. While aftermarket blocks often utilize splayed four-bolt main caps to combat this, not everyone has the budget to buy one. Main cap girdles, such as the D.S.S. Main Support System pictured here, are a cost-effective way to add strength to a production block. While some girdles are made from steel, the D.S.S. piece is made from billet 6061-T6 aluminum to effectively dampen damaging harmonics, which the company says virtually eliminates main bearing walk.
10. The aftermarket keeps...
10. The aftermarket keeps the Ford enthusiast bathed in a variety of new parts. This is one of Ford Racing’s engine blocks, the Boss 302, which offers a much higher limit for cubic inches and horsepower ratings. Combining the block’s 4.125-inch bore with a 3.400-inch stroke crankshaft can give 364 cubic inches of life back to your 302-powered vehicle.