Can hydraulic lifters cause inadequate full power?

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

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* Cory Papenfuss, Ph.D. Electrical Engineering, PPSEL-IA *
* Research Associate, Vibrations and Acoustics Laboratory *
* Mechanical Engineering *
* Virginia Polytechnic Institute and State University *
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