Hydraulic lifters maintain...
Hydraulic lifters maintain a preload between the lifter and the pushrod to prevent clatter, but an aggressive high-performance lobe can still be noisy even with the lifters properly adjusted.
Valvetrain Clatter
71BigBlockNova, via CarCraft.com: Perhaps it's because I don't have an experienced ear yet, but I think my valvetrain is making too much noise. How much noise should you hear from a hydraulic lifter engine with the valve cover off? Should the rockers be silent or should there be a little clatter?
Jeff Smith: This is an interesting topic. Original-equipment engines have to do more than just be durable, they also have to be quiet. Assuming all the valvetrain pieces are installed and functioning properly, there should be no noise emanating from a hydraulic lifter-equipped engine. Generally, a loose adjustment, where there is clearance between the rocker arm and the pushrod and/or valve tip, will create this clatter. This is what you hear on a mechanical-lifter engine that relies on a small amount of clearance or lash to accommodate expansion as the engine warms up.
An interesting thing happens with aftermarket, high-performance camshafts. As camshaft profiling has progressed, designers have gradually created much more aggressive cam lobes. This means the lobe shape accelerates the lifter much more quickly compared with stock profiles. This is one way to increase the amount of valve lift compared to the duration. The price for this more radical lobe profile is valvetrain noise. Even with proper preload on the lifter and high-quality parts, a more aggressive lobe will tend to clatter, even at low engine speeds such as just off idle. Not all current high-performance cams are noisy. For example, every cam manufacturer offers several levels of camshafts that appear to have similar specs. The more aggressive the cam profile, the more lift it will generate for the same amount of duration at 0.050 inch of tappet lift. These cams will also produce the most noise.
Another point worth mentioning is the zinc and phosphorus levels in current production engine oil have been reduced in the last five years or so to meet increasingly stringent requirements from the OE companies. This requirement is intended to reduce the levels of these additives to improve catalytic converter life in the face of 100,000-mile warranty standards. Zinc and phosphorus are two high-pressure additives that are important to help prevent wear, especially in engines with flat-tappet lifters. Break-in procedures for a new cam should include a bottle of antiwear additive that is sold through the major cam companies like Comp and Crane.
But the problem doesn't stop there. Many cam companies now suggest using engine oils with higher levels of zinc and phosphorus for engines equipped with flat-tappet lifters. Shell Rotella T is diesel-engine oil that offers these increased antiwear additives and is safe to use in gasoline engines. Another alternative is using one of the high-performance oils from Quaker State, such as the Q racing oils, which also contain higher levels of antiwear additives and can be used safely in street engines. The oils cost a little more, but they may also prevent a flat-lobe problem down the road.
A Question Of Balance
Crusher via CarCraft.com: I want to get my 383 balanced. I know the pieces needed are the crank, pistons, rods, flywheel, and harmonic balancer. What kind of harmonic balancer do I need to buy and what flywheel do I need? I am using a cast Eagle crank. I don't know if the harmonic balancer I need is external or internal and if I need one for a 350 or a 400? Is an 8-inch balancer sufficient? Are there differences for flywheels for a 350 versus a 400? Also, the car this engine is going into has a Muncie four-speed and a 350. Will I still be able to use the transmission in my '71 Nova if I need a 400 flywheel (assuming the flywheels are different)? I know I will need a new-size clutch if a new flywheel is needed.
Jeff Smith: This is a great question, since Eagle makes both an internally and externally balanced stroker crank for the small-block Chevy with a two-piece (old-style) rear main seal. Since it is difficult to identify the difference, you should call Eagle and give them your crank part number to make sure you know which style of crank you have.