Kip Fabre

Many people comment and talk about hydraulic lifter noise. The first question is “why do we have hydraulic lifters”? They were first put into street cars back in the 1950’s so that the engines did not have to have the valves adjusted after engine “break in”. In fact, on a stock engine they never have to be reset. But even back then, the high performance cars, and the trucks, and the industrial engines, all still had solid lifters. What is “lifter noise”? Preload? Probably not. If the check valve in the lifter seals and it is able to hold pressure, and you have enough preload for the expansion of the block and heads, the lifter is pretty much quiet. The hydraulic lifter is the most accurately machined part in the whole engine, with tolerances necessarily held to the fifth decimal place (.00001”). If the lifter has just a little more internal clearance than it should, you will have a lifter tap, which in reality is a valve tap. Low oil pressure at idle and high spring pressure will cause the lifter to leak down and not maintain preload. Some other sources of the noises are very aggressive or harsh cam lobe designs (You know, the ones that make all that extra power). As the lifter is coming up off the base circle of the cam, the lobe impacts the lifter with the loading of the pushrod, rocker arm, spring, and valve, the pressure and impact causes a radial expansion of the lifter body, increasing the clearance between the plunger and body, causing the plunger to drop down, which causes the valve train to have clearance, which makes the valve tap. It is the harsh opening that gets the valve train in trouble and causes the clearance that you hear at valve closing. The reason you don’t have valve train noise with a stock cam is because stock cam lobes are designed to be smooth and quiet and not tear up lifters or valve train parts. Lifter bores are the next problem. If the lifter bore has extra clearance, meaning just a few extra tenths (.0001”), the lifter can be noisy because it doesn’t allow enough oil to get into the lifter to maintain preload. All of these preload numbers I see people recommending here on this site, whether it is .030”, .050”, .070”, .080”, .090”, or .110”, don’t matter as far as lifter noise goes, I believe.

andysc

iTrader: (6)

Great post, alot of good info there. I am experiencing this very issue now. I had my heads rebuilt, new valve springs, and I am getting this condition. I am checking my lifters, adjustments are good, so may be valve tap instead of a lifter issue.

tia

andy schuck

RezinTexas

very interesting read, thanks for the info