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.

 

Interesting read... Thanks for sharing.

 

How does that work? More clearance equals less oil flow?

 

More lifter clearance in the bore will bleed off presser to the lifter.

 

That's something you would read on a gauge though, right? It's not like you'll be seeing 50psi hot idle and the lifters still aren't able to fill.

 

The level of oil pressure indicated on the gauge is point specific and only tells you the how pressure there at the sensor's location, which is at the top on the engine downstream of the oil filter, but upstream of the lifters and the bearings.

The level of pressure for any particular lifter on the other hand is a function of the level of force with which the oil arrives at the lifter divided by the area over which the pressure is to be distributed. To the extent a particular lifter has excess clearance the effective oil pressure (at the lifter) would be reduced as it is spent filling the excess clearance and filling the lifter.

So, to the extent an engine had one more lifters with excess clearance, the level of pressure indicated on the gauge would be slightly less (e.g. 48 pounds) than the same engine would have with no lifter bores with excess clearance (e.g. 50 pounds). But the pressure gauge alone would not indicate the presence of excess clearance in single lifter bore, or bearing for that matter.

 

Right, but it's not a exactly a question of oil pressure indicating excess clearance at the lifter bore(s). 48psi should still keep the lifter operating correctly and quietly.

If you already have relatively healthy oil pressure, will a little excess clearance of a couple tenths really have a profound enough affect to cause a noticeable tick or tap? I would think you would already be seeing relatively low oil pressure for the difference between the pressure at the lifter and pressure at the sensor to hurt lifter operation.

 

Assume a 50 pounds of oil pressure at the sensor, in a engine that is 100% healthy except for a single oversize lifter bore. That one lifter bore would only represent 1/16th of the lifter system and even a smaller fraction of the total oil system downstream of the sensor. Given those facts, the effect of the single oversize lifter bore on system oil pressure could be pretty small.

As to how much excess clearance could reduce the oil pressure to the individual oversize lifter bore, I don't know, but I could envision it cutting the pressure in half. The oil will obviously flow to the area with the least resistance, but I don't know the relative resistance of the lifter internal chamber vs that of the external clearance.

Clearly if all 16 lifter bores are over size the pressure will be significantly affected and readily apparent at the sensor.

 

Great post. I'd like to add a few things as well.

Lifter noise can be caused from many different issues within the lifter itself. As Kip mentioned, lifter tolerances are within .00001", which leaves minimal room for error. Theoretically a lifter should be able to stay "pumped up" even with low oil pressures. We've tested our stuff at idle with 8psi and 300* oil temperatures, for thousands of hours. This is pure hell on lifters, mostly the roller bearings, but they will survive.

The problem with most lifters is they're batch produced and use the entire tolerance window. This allows the highest percentage of parts to get through (pass) the equipment making them. When you start throwing heavy spring pressures and radical camshaft profiles at these batch produced parts, things can make noise and potentially fail. This happens because the hydraulic function of the lifter can't keep up. Lifter to bore clearance does play some roll, but even with .0025"-.003" clearance the lifter should still have enough oil available to function. We typically see a 5-10psi drop for every .001" extra clearance in all 16 bores. The real problem is when you don't have enough clearance. Ideally you want .0015" +/- .0005" clearance.

The preload should reflect the internals of the lifters themselves, and should be specified by the manufacture. The plunger inside of the lifter body needs to be in the correct position for oil to fill the chambers properly, providing the best performance while staying quiet. If one lifter is making more noise than the others, and requires more or less preload....9 times out of 10 it's because of a taper inside the lifter body.

See you Monday Kip!