<VV> Lifter pre-oil

[Mark Durham]

Cool, another aircraft mechanic on VV. Yes, John most aircraft piston
engines run on hydraulic lifters that look uncanny like our GM ones.
They were installed the same way, un primed, with the cam lube on the
bottom face and a engine oil mixture on the sides. Like Stephen, I
never had a hydraulic lifter failure in 18 years of building aircraft
engines or 42 years of automotive engines.

The lifters come with enough oil to protect the internal parts for the
short time it takes to pump them up, and you run the risk of over
extending the valves and putting extra stress on the cam lobes by over
compressing the springs (the pressure goes up expodentially, by the
way) if the lifter is already pumped up and cannot release the fluid
to adjust itself. Its obvious this scenario is not good for a cam lobe
trying to break in.

First start with flat lifters is good for the cam lobes, because the
lifters pump up in increments each time they cycle which incrementally
increases presssure on the lobe until zero lash is set. The lobe has
had a chance to go through multiple cycles with incremental pressure
increases until zero lash, a good thing for lobe break-in.

If you look at the lifter design, they are made to compensate for wear
and to pump up  and hold the pressure. The design is one way, the
dimensions at startup are loose until oil pumps it up to fit each
unique cam lobe, lifter, push rod, rocker arm and valve configuration.
The lifter expands to do that. It expands to take care of wear.

There is no provision to leak oil out to make that adjustment. Yes, it
happens, but it is working against the design to do so. That is why
all adjustment information says to adjust lifters in slowly when you
do, so the lifters can compensate without overstressing the cam lobe,
lifter bottom, springs or the valve actually hit the piston (don't
know if it can happen in this engine but it can on others.

Stephen, drop me a note off line and we'll compare A&P stories.  Mark Durham

On Mon, Jan 3, 2011 at 1:26 PM,  <jvhroberts at aol.com> wrote:
> Aircraft engines have hydraulic lifters?
>
> John Roberts
>
> -----Original Message-----
> From: Stephen Till <still63 at att.net>
> To: VirtualVairs at corvair.org
> Sent: Mon, Jan 3, 2011 4:18 pm
> Subject: <VV> Lifter pre-oil
>
>
> I overhauled aircraft engines for 16 years. lifter face to cam were
> lubed with
> break in lube and lifter were pre-oiled on engine pre-oil before live
> run.
> I Never had lifter failure. If you have oil pressure a lifter will
> eventually
> pump up. Be easy on the engine on a fresh overhaul.
>  Good luck-Stephen Till
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