Flow rate of oil into hydraulic valve lifter

[chuck8892]

Strange request: I was investigating why some hydraulic lifters I installed in my car were allowing the push rods to pop off. I have since discovered that the two different lifter brands in question had two different hole sizes that allow the oil to enter the lifter. This oil pressurizes the lifter's spring-assisted plunger, thus taking all of the slack out of the valve train assembly. The OEM lifters have an oil hole dia. = 0.092" and the replacement lifter holes have dia. = 0.067".

I think the flow rate into the lifters should be directly proportional to the hole area: Q1=V*A1 & Q2=V*A2, where V is the same for both since the oil pressure/volume are assumed constant. Based on that, the replacement lifters have a flow rate 53% that of the OEM lifters, taking nearly twice as long to come to full pressure. In my estimation, this is allowing slack to occur in the valve train and thus the push rods to come off the rocker arms.

Independent of an auto mechanic-specific perspective, does this reasoning check with the piping & fluid mechanics experts? I realize I simplified and made a lot of assumptions. Thanks for the help!

 

[MikeHalloran]

I could swear that hydraulic lifters also had a light spring inside them, to prevent exactly that problem.

As for the flow rate, you can increase it quite a lot by radiusing the edge of the fill orifice, if you want to screw around with them.

It's probably easier to just bleed the air out by exercising them while immersed in a bucket of oil, just before putting them in the engine.





Mike Halloran
Pembroke Pines, FL, USA