<VV> now lifter oil loss

[James Davis]

Any time lifters "pump up" it is because of loft on the cam lobe nose 
.  In other words the lifter is not following the cam lobe.  Cure is 
heavier valve springs, different cam lobe profile,  lighter valve 
train components, stiffer push rods, less rpm ;-).   The usual 
culprit valve is operating the engine at a rpm that is at the valve 
spring resonance frequency or one of its harmonic 
frequencies.  Lifter collapsing can be due to several problems: low 
oil pressure, oil contamination, lifter pump clearance, non circular 
base circle on the camshaft, high valve spring pressure; to name a 
few.  .Usually lifters that work correctly when the oil temperature 
is cool and collapse when the engine oil is hot is due to the oil 
viscosity/valve spring pressure.   In other words, the lifter pump 
relief valve cannot overcome the valve spring pressure plus valve 
train inertia pressures at high rpm.
Jim Davis.


At 10:19 AM 12/21/2007, BBRT wrote:
>Question. In a racing Corvair engine , running stock pump, remote 
>cooler, 10 psi per thousand rpm ~ 70 psi or so, hydraulic lifters, 
>turning up to 7500 rpm, why do lifters lose their adjustment, 
>meaning clacking like the oil within the lifter is low, after a half 
>hour on track? Are they improperly adjusted (nominal 5/8 turn)? Do 
>the valves float causing the lifter not to continue to " pump up"? 
>What is happening?
>
>Chuck S
>
>
>
>From: "John Kepler" <jekepler at amplex.net>
>>FWIW, "stock" oil pumps move MUCH more oil than an engine can reasonably
>>handle, that's why there's a by-pass valve in the pump.  Just because a
>>little is good, a lot isn't necessarily better!
>>
>>John