Spring spacers are to correct spring installation hight variances. When the valve seat is cut, this makes the valve itself set deeper into the head. This also makes the stem side stick out farther from the head. With the stem sticking out farther, the spring pocket is now longer. To keep all the spring pockets the same length, spacers are added.
If the machinist cuts each seat to the same depth, then all the spring pockets will have the same amount of spacers, but if the machinists varies each seat cut, you end up with different amounts at each valve. Both ways work work just fine, buy cutting only whats needed to clean up each seat, you end up with the odd spacer counts. Some machinist will find the lowest seat then cut all the rest to the same depth, this makes assembly easier but can remove more material then needed.
Every valve spring has a load rating. Seat pressure is how much pressure the spring applies to the valve to hold it closed when the cam is NOT acting on it. Open pressure is the amount of force trying to shut the valve when fully opened by the camshaft. To keep all valves under equal force, spring shims are used to set the seat pressure to factory specifications. If the springs are getting weak and shims are used to compensate, you can end up with a coil bind situation. Coil bind is where the coils make contact with each other and form a solid mass, bent pushrods or broken studs are the results. At full valve lift, you should have clearance between each coil in every spring, ( .060" ) is the minimum amount you want.
When setting coil springs, a small, special tool is used to measure each one. (
http://www.summitracing.com/parts/cca-4929 )
Shims come in .015", .030", and .060" thicknesses, so being with in .015" is ideal, .030" is usually close enough. It you do not know the actual factory spring setting, next best thing is to set them all close to each other with out binding the coils at full lift. Shims also come in soft and hardened material. The hardened shims go up against the valve spring, softer shims go against the head surface. In high spring rate heads, the valve springs can wear away the cast iron or aluminum heads so the hardened shims prevent this. In your application, it's not going to be a problem.
Joe
