In article ,
wrote:

Hey all. I posted a week or so ago about low power in my Cherokee, but the
signal-to-noise ratio
was low with all the things we've tried in the past. We're basically at the
point of asking if
mismatched hydraulic lifters could cause chronic low power. The overhaul was
done before we bought the
plane by a shade-tree mechanic, so I would not be at all surprised if the
lifter bodies and plungers were
mixed and matched. Last year, we swapped out pushrods to get dry tappet
clearance correct, and that
seems to have corrected an *intermittent* power loss at the first takeoff of
the day we had then I was
skeptical that the lifters would be inadequate to make up the difference, but
it hasn't done that for a
year so it seems to have fixed the intermittent problem.

SO, I was thinking that maybe if the lifters were mismatched, they would
still pass the Service
Instruction 1011 we did last year, but not have correct bleed-down rates. We
checked lifters for being
straight, no stuck ball valves, and they'd spring back when assembled dry.

Can lifters with marginal bleed-down rates truly be responsible for what I'd
guess is ~10 hp
at full power? I can see making it idle badly, but the time for bleed-down
is much lower at max RPM.

Thoughts? Opinions? Without some definative reasoning, it seems silly to
spend $600 in an experiment?

Thanks,
-Cory

You would HEAR tappets clicking if you have bad lifters.

Cams in Lycomings tend to corrode on the front lobes over time, with low
usage. One way to check is to pull the valve covers and check the valves
for proper movement as the crank turns.

Check the logs for cam replacement at overhaul.

--
Remove _'s from email address to talk to me.