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

--

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

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.

Orval Fairbairn wrote:
: 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.

The overhaul had yellow tag for the cam. Put a dial indicator on the cam last year and it came up at 0.353 +- 2 on all lobes... that agreed with a friend's brand new
PMA's cam lift. I'm fully convinced the cam is fine.

If the lifters had clogged valves, I'd agree that you'd hear them, but excessive leakdown maybe not? Like I said, I don't *really* believe this is the problem, but I
didn't believe the dry tappet clearance would affect anything either (but did). We've checked everything else anyone's ever come up with (check my post from a week ago).

Thanks,
-Cory

--

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

I Don't know the answer to your question but I'm wondering if the
airbox was changed with The STC. Is it possible the engine is hungry
for air at full throttle?

Drew Dalgleish wrote:
: I Don't know the answer to your question but I'm wondering if the
: airbox was changed with The STC. Is it possible the engine is hungry
: for air at full throttle?

This engine upgrade is extra weird because the owner who did it
(the guy we bought it from) also got a field approval for changing it
firewall-forward to the fiberglass clamshell cowling like later-model
-180's. So, it's got the mufflers and two exhausts that exit by the
nosewheel. That and the updated air box should provide good power.

We added and manifold pressure gauge to it as an optional STC
component, even though it's fixed-pitch prop. As far as air restriction,
I've discounted that because the manifold pressure gauge reads about 1.5"
less than ambient pressure.... right about where it should be as far as
losses in the intake. For example, at the 2100' field elevation we're at,
a typical day would read 28" before starting. Full-power static runup
shows about 26.5".

I've also discounted an improper (lean) mixture due to jetting,
carb float level, fuel pressure, etc because it requires leaning when the
DA reaches about 3500' in order to make max power.... right about where it
should. If it were too lean, it wouldn't do that until quite a bit higher
DA (and we've have melted the pistons when we run autogas).

-Cory


--

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

On Oct 7, 2:33*pm, wrote:
Drew Dalgleish wrote:

: * I Don't know the answer to your question but I'm wondering if the
: airbox was changed with The STC. Is it possible the engine is hungry
: for air at full throttle?

* * * * This engine upgrade is extra weird because the owner who did it
(the guy we bought it from) also got a field approval for changing it
firewall-forward to the fiberglass clamshell cowling like later-model
-180's. *So, it's got the mufflers and two exhausts that exit by the
nosewheel. *That and the updated air box should provide good power. *

* * * * We added and manifold pressure gauge to it as an optional STC
component, even though it's fixed-pitch prop. *As far as air restriction,
I've discounted that because the manifold pressure gauge reads about 1.5"
less than ambient pressure.... right about where it should be as far as
losses in the intake. For example, at the 2100' field elevation we're at,
a typical day would read 28" before starting. *Full-power static runup
shows about 26.5".

* * * * I've also discounted an improper (lean) mixture due to jetting,
carb float level, fuel pressure, etc because it requires leaning when the
DA reaches about 3500' in order to make max power.... right about where it
should. *If it were too lean, it wouldn't do that until quite a bit higher
DA (and we've have melted the pistons when we run autogas).

-Cory

--

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

Sometimes a weak valve spring(s) will manifest itself in a loss of
hp.

On Tue, 7 Oct 2008 13:10:26 +0000 (UTC),
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

your prop has 6 bolts. all symetrical. the prop can sit in many
positions relative to the piston positions.

I remember a thread about a dozen years ago where the prop position
was found to have a noticeable effect on the power out of the engine.
something to do with the coinciding of the blade wash across the inlet
at the time of air suck. (substitute your own technical terms)

you look to be heading to my sort of insanity (my carby fix took 18
months and $2,500 but by hell I understand the bugger now)
comiserations!

try changing your prop position relative to the crank. a spool of
lockwire and some lockwire pliers should be cheaper than $600.

Stealth Pilot

Stealth Pilot wrote:
: your prop has 6 bolts. all symetrical. the prop can sit in many
: positions relative to the piston positions.

: I remember a thread about a dozen years ago where the prop position
: was found to have a noticeable effect on the power out of the engine.
: something to do with the coinciding of the blade wash across the inlet
: at the time of air suck. (substitute your own technical terms)

: you look to be heading to my sort of insanity (my carby fix took 18
: months and $2,500 but by hell I understand the bugger now)
: comiserations!

: try changing your prop position relative to the crank. a spool of
: lockwire and some lockwire pliers should be cheaper than $600.

: Stealth Pilot

Good thought, although I'm not sure that I buy into the propwash making pulsating
ram air. In any event, we re-indexed the prop awhile back and it made no effect on either
vibration or power output. The irritating thing is that the PA28 service manual specifies
the prop indexing in an ambiguous way. It says to put it on at 2 o-clock and 8 o-clock
at TDC. That's not an option though... the 6-holes line up at either the 12-6 or 10-4
position. Either position is halfway incorrect (but we've done both to no effect). Even
if it did have an effect, it would show up as an increase in manifold pressure.

Thanks for playing.... Welcome to my hell.

-Cory

--

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

On Oct 10, 9:38*am, wrote:

* * * * Good thought, although I'm not sure that I buy into the propwash making pulsating
ram air. *In any event, we re-indexed the prop awhile back and it made no effect on either
vibration or power output. *The irritating thing is that the PA28 service manual specifies
the prop indexing in an ambiguous way. *It says to put it on at 2 o-clock and 8 o-clock
at TDC. *That's not an option though... the 6-holes line up at either the 12-6 or 10-4
position. *Either position is halfway incorrect (but we've done both to no effect). *Even
if it did have an effect, it would show up as an increase in manifold pressure.

Prop blast can have an effect on the carb, but usually only on
installations with poor cowling designs or open intakes. Older 182s
and some 172s, for instance, will run roughly with the cowl off, and
run fine after it's installed. With it off, the air pulses off the
prop will strike the airbox inlet and upset the pressures in the
venturi, upsetting fuel flow from the nozzle and creating uneven
mixtures to various cylinders. With the cowl on, the air flows PAST
the intake filter rather than AGAINST it and the pressures aren't
disturbed so much.
Some homebuilders have had problems with this and turning the
intake away from the front fixes it.

Has anyone looked at your mufflers for loose baffling that might
be blocking the oulets?

Have the mags been checked? Electrical problems are the biggest
single source of trouble.

If the carb is a Marvel Schebler/Precision Airmotive unit, have
the ADs been done with regard to the two-piece venturi and fuel
nozzle?

Dan

: Prop blast can have an effect on the carb, but usually only on
: installations with poor cowling designs or open intakes. Older 182s
: and some 172s, for instance, will run roughly with the cowl off, and
: run fine after it's installed. With it off, the air pulses off the
: prop will strike the airbox inlet and upset the pressures in the
: venturi, upsetting fuel flow from the nozzle and creating uneven
: mixtures to various cylinders. With the cowl on, the air flows PAST
: the intake filter rather than AGAINST it and the pressures aren't
: disturbed so much.
: Some homebuilders have had problems with this and turning the
: intake away from the front fixes it.

I'd say this later-model PA28 cowling is a "good" one. In any event,
I'd think prop-wash-induced boost air would show up as a manifold pressure
increase, and uneven fuel distribution as dissimilar EGT. Neither is present.

: Has anyone looked at your mufflers for loose baffling that might
: be blocking the oulets?

Yes... each year for annual. Brand new mufflers last year for other
reasons... No change.

: Have the mags been checked? Electrical problems are the biggest
: single source of trouble.

We've put new points and condensers in both, including internally (and
of course externally) timing them. No change. I've done full-power mag checks
and misfires would be apparent in that case. New plugs make no change, either.

: If the carb is a Marvel Schebler/Precision Airmotive unit, have
: the ADs been done with regard to the two-piece venturi and fuel
: nozzle?

Venturi AD's checked and CW. Restriction or mixture would show up as low
MP or abnormal EGTs anyway, no? Neither is the present.

Thanks,
-Cory

--

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