Hey all. Question about my Cherokee's O-360. When we first got it about 3.5
years ago, it was very low hours SOH, but almost 10 years. We had some sticking
valves and bad oil consumption, so sent the jugs out to have the IRAN. At that time,
in addition to the the IRAN, a few rusted valve springs were replaced with servicable
ones by Triad Aviation. Broke in and settled on about 1qt/8 hours on chrome jugs...
good by all I've talked to. Ran fine, although the max static runup I'd ever seen was
right in the midrange.... 2350 or so. Often it was on the low end... 2275-2300.

For a little while now (6 months or so), it seems to have a bit of
"mid-morning" sickness. It starts up and runs smooth and fine. Taxis smooth, runup
good, mags fine. On the takeoff/climbout, it just doesn't "feel right." Not bad
enough to know something's amiss, just enough to look at the VSI and say, "Hrm... I
should be getting a little better climb than this." Usually within a minute or two of
liftoff, it picks back up and I get an additionall 200 fpm or so. The usual
in-flight diagnostics reveal nothing.... mixture, carb heat, mags, fuel pressure,
CHT/EGT, etc. Runs smooth on either mag (with reduced power)... on high DA days
leaning it a bit might be necessary, etc.

Sounds a lot like a sticking valve, but I think I've done everything that can
be done to prevent that. Baffling is in great shape. I never allow climb CHT over
400 or cruise over 380... and that's on the *spark-plug* CHT probes... They've been
verified reading at 50-60 degrees hotter than the bayonet-style that Lycoming uses, so
the CHT is actually 325-350 max. I generally cruise no higher than 65% and lean to
about peak EGT as per Piper/Lycoming recommendations, so there shouldn't be much for
rich combustion byproduct buildup.

Other suggestions? I'm figuring to pull off the rocker-box covers, push on
the valves, and see if I can feel friction in any of them.

Thanks,
-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

On Mon, 16 Jan 2006 14:40:46 +0000 (UTC),
wrote:

Your engine is probably not creating the full 180hp, which leads to
the low static RPM at runup, and the less than normal takeoff
performance.

Now the question is: What is causing the low power output?

> Sounds a lot like a sticking valve, but I think I've done everything that can

I am not an expert, but in my (one) experience with a stuck valve - I
could hear it chatter when it stuck. It was not the kind of thing you
could overlook. Perhaps there are other ways for valves to stick
without chattering, but I thought I would at least provide you this
datapoint.

What are the compressions? Very low compression can be cause poor
power output.

Another possibility is a worn camshaft, and hence the inability to
fully lift the valves. This results in low power output. On an
engine that had low usage for its first 10 years SMOH, it should be a
concern. There are many archived threads on google groups discussing
camshaft rust and the subsequent damage to the camshaft.

Seeing any metal in the filter on oil changes? Do you do oil
analysis? If so, this could help confirm the latter theory. Also, I
believe there is a way to measure the valve lift and compare against
tolerances to see if the cam and lifters are doing their job.

-Nathan

: Now the question is: What is causing the low power output?

... but it's intermitent and subtle. The low power has always been "within
spec" as per runup, just always at the low end.

: > Sounds a lot like a sticking valve, but I think I've done everything that can

: I am not an expert, but in my (one) experience with a stuck valve - I
: could hear it chatter when it stuck. It was not the kind of thing you
: could overlook. Perhaps there are other ways for valves to stick
: without chattering, but I thought I would at least provide you this
: datapoint.

: What are the compressions? Very low compression can be cause poor
: power output.

All compression tests have been excellent... generally 79/80 or 80/80. Once I
had one at 78/80. When the valves and rings seat up for a compression test, all is
good.

: Another possibility is a worn camshaft, and hence the inability to
: fully lift the valves. This results in low power output. On an
: engine that had low usage for its first 10 years SMOH, it should be a
: concern. There are many archived threads on google groups discussing
: camshaft rust and the subsequent damage to the camshaft.

I've looked into those for years as a concern for this engine given its
history. When we had the jugs off last time, I looked at the cam carefully. I could
see no visible evidence of rusting, pitting, or spalling. The tappets (from what I
could see without splitting the case) looked good too. Besides, I cannot see how a
worn cam would suddenly become unworn 60 seconds after takeoff.

: Seeing any metal in the filter on oil changes? Do you do oil
: analysis? If so, this could help confirm the latter theory. Also, I
: believe there is a way to measure the valve lift and compare against
: tolerances to see if the cam and lifters are doing their job.

I do not send out for oil analysis, but I cut open the filter. Never more
than a couple tiny specs of metal or carbon in the filter.... certainly within
"normal" limits.

I'm planning on measuring the lift when I've got the covers off. I need to
build some sort of jig for a dial indicator and figure out a way to drain the lifters
of all oil. Does anyone know what the lift is supposed to be? IIRC it's not a
"normal" maintenance check item so it's not in the books.

Thanks for the comments, though... I think we're in the same spot.

-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Have you done the "wobble check" on the valves?

wrote:
> Hey all. Question about my Cherokee's O-360. When we first got it about 3.5
> years ago, it was very low hours SOH, but almost 10 years. We had some sticking
> valves and bad oil consumption, so sent the jugs out to have the IRAN. At that time,
> in addition to the the IRAN, a few rusted valve springs were replaced with servicable
> ones by Triad Aviation. Broke in and settled on about 1qt/8 hours on chrome jugs...
> good by all I've talked to. Ran fine, although the max static runup I'd ever seen was
> right in the midrange.... 2350 or so. Often it was on the low end... 2275-2300.
>
> For a little while now (6 months or so), it seems to have a bit of
> "mid-morning" sickness. It starts up and runs smooth and fine. Taxis smooth, runup
> good, mags fine. On the takeoff/climbout, it just doesn't "feel right." Not bad
> enough to know something's amiss, just enough to look at the VSI and say, "Hrm... I
> should be getting a little better climb than this." Usually within a minute or two of
> liftoff, it picks back up and I get an additionall 200 fpm or so. The usual
> in-flight diagnostics reveal nothing.... mixture, carb heat, mags, fuel pressure,
> CHT/EGT, etc. Runs smooth on either mag (with reduced power)... on high DA days
> leaning it a bit might be necessary, etc.
>
> Sounds a lot like a sticking valve, but I think I've done everything that can
> be done to prevent that. Baffling is in great shape. I never allow climb CHT over
> 400 or cruise over 380... and that's on the *spark-plug* CHT probes... They've been
> verified reading at 50-60 degrees hotter than the bayonet-style that Lycoming uses, so
> the CHT is actually 325-350 max. I generally cruise no higher than 65% and lean to
> about peak EGT as per Piper/Lycoming recommendations, so there shouldn't be much for
> rich combustion byproduct buildup.
>
> Other suggestions? I'm figuring to pull off the rocker-box covers, push on
> the valves, and see if I can feel friction in any of them.
>
> Thanks,
> -Cory
>

Nathan Young wrote:

> Another possibility is a worn camshaft, and hence the inability to
> fully lift the valves.

If the cam is worn, performance will not improve after a few minutes.

George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.

Hmm, your reported 79/80 seems excessive, even for 3 year old jugs...
Perhaps the mechanic needs to test his differential compression rig
against a calibrated orifice...

First, do a bit of investigation...
Physically look up in the carb and see that the butterfly opens all the
way at full throttle... Ya, ya, ya, I know that means you have to
remove the cowling...
If you are not sure where full open is <it's actually a hair past
straight up and down> pull the bolt out of the throttle cable end and
how it opens then put the bolt back in... Should be the same....
Make sure the heat box flapper is tightly closed... Use mirrors and
bright lighting...
Visually inspect the entire air intake tube for any blockage... <ditto>
Fly it without the air filter to see if that makes a difference...
Measure the fuel pressure at the carburetor, with an external gauge, at
full throttle...
Check the fuel level in the bowl (a biggie - this is often way off)...
Test run the electric pump with the fuel line dumping into a measuring
can to ensure you
are getting rated fuel flow...
Make the mechanic prove to you that the mags are all timed at 25
degrees... <are the
mags roughly at mid range on their adjustment slots - if all the way to
one end you could have a worn acessory gear>
Verify that the impulse cam (spark retard) is releasing after the
engine starts...
What is the difference in static rpm on L mag versus R mag?
Verify that the prop has the correct pitch... <another biggie>

If nothing is found above, then rig up a dial indicator and measure the
lift on each valve, could be illuminating... I wouldn't worry about
oil in the lifters... Just do each measurement 3 or 4 times... Call
Lycoming, they can give you the lift specs...
If the cam looks OK then pull the rocker arms to:
1. See how the bushings look.. If egg shaped you are losing lift and
power... Don't let
some yahoo try to tell you that the hydraulic lifters make up for this
- they do not!
2. see if the valves are free... WIth the rocker out of the way you can
use a lever to
depress each valve for sticking... The exhaust are the ones to be
suspicious of... If any doubt rope the cylinder and remove the valve
spring and see if the valve is free...

If everything mechanical seems up to specs then squirt solvent oil down
each valve stem and work the valve up and down (WD40, Mouse milk,
Marvel Mystery Oil, etc.) then change oil for a fill up of lightest
weight oil you can get < leave the filter as is> add a can of AVBLEND
and a pint of MMO (Marvel Mystery Oil) to the fill up, and go fly the
heck out of it for 5 hours... See if that solves it...

denny

On Mon, 16 Jan 2006 16:05:26 +0000 (UTC),
wrote:


> I've looked into those for years as a concern for this engine given its
>history. When we had the jugs off last time, I looked at the cam carefully. I could
>see no visible evidence of rusting, pitting, or spalling. The tappets (from what I
>could see without splitting the case) looked good too. Besides, I cannot see how a
>worn cam would suddenly become unworn 60 seconds after takeoff.

Agree, it would be tough for the lobes to grow back!

Curious. Do you transition to a cruise climb or stay at Vy for
climbing?

Nathan Young > wrote:
: > I've looked into those for years as a concern for this engine given its
: >history. When we had the jugs off last time, I looked at the cam carefully. I could
: >see no visible evidence of rusting, pitting, or spalling. The tappets (from what I
: >could see without splitting the case) looked good too. Besides, I cannot see how a
: >worn cam would suddenly become unworn 60 seconds after takeoff.

: Agree, it would be tough for the lobes to grow back!

: Curious. Do you transition to a cruise climb or stay at Vy for
: climbing?

I generally climb out at at least 100 mph (Vy = 85) to keep the jugs cool. In
a LONG climb (6-10kft) I'll monitor the CHT closely and step-climb if they get too
high.

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Otis Winslow > wrote:
: Have you done the "wobble check" on the valves?

Not since the shop did the IRAN 3 years ago. It was the relatively close-by
Triad (Lycoming certified repair center), so I'd assume that was part of the
inspection.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

I'll respond with what I've done:

Denny > wrote:
: Hmm, your reported 79/80 seems excessive, even for 3 year old jugs...
: Perhaps the mechanic needs to test his differential compression rig
: against a calibrated orifice...

He used to have an old simple differential compression rig that I admit I was
skeptical of 79/80-80/80 on. The last few times has been with a brand new gauge set
with extra calibrated orifice for his own Continental TSIO-360. I believe the numbers
(also cannot hear any leaking at all through intake, exhaust, or breather tube).

: First, do a bit of investigation...
: Physically look up in the carb and see that the butterfly opens all the
: way at full throttle... Ya, ya, ya, I know that means you have to
: remove the cowling...
: If you are not sure where full open is <it's actually a hair past
: straight up and down> pull the bolt out of the throttle cable end and
: how it opens then put the bolt back in... Should be the same....
: Make sure the heat box flapper is tightly closed... Use mirrors and
: bright lighting...
I haven't visually verified the actual carb butterfly, but I have looked at
the rest of the system recently (and after the problem first manifested). Heater box
flapper is good, as is the rest of the air intake tube. I've
field-approved a MP gauge on it and I saw 26" MP at 3500 MSL last night.... I'd
believe that for full-throttle.

: Visually inspect the entire air intake tube for any blockage... <ditto>
: Fly it without the air filter to see if that makes a difference...
Haven't flown without, but new filter FWIW.

: Measure the fuel pressure at the carburetor, with an external gauge, at
: full throttle...
I've got the autofuel STC so the pumps are a bit different than stock. I've
watched the pressure carefully since insect parts found their way into a fuel line off
the right tank once... that was exciting too. At full power, power-on-stall attitude,
the pressure will drop down to 2 psi or so with the engine pump, but the electric
boost brings it back up to 4-5 no matter what. This is on the stock gauge in the
panel and is measured at the carb.

: Check the fuel level in the bowl (a biggie - this is often way off)...
Have not looked at this.

: Test run the electric pump with the fuel line dumping into a measuring
: can to ensure you
: are getting rated fuel flow...
Have not done this, although watching the fuel pressure go up/down a bit with
power and attitude make me believe that it's all OK.

: Make the mechanic prove to you that the mags are all timed at 25
: degrees... <are the
: mags roughly at mid range on their adjustment slots - if all the way to
: one end you could have a worn acessory gear>
I timed them myself with my mechanic there a number of times. We have also
swapped points and re-timed the internal timing of both. Before/after timing (it was
only off by 1-2 degrees ever) the problem persisted.

: Verify that the impulse cam (spark retard) is releasing after the
: engine starts...
Mag drop is normal when up to speed, so it must be, right?

: What is the difference in static rpm on L mag versus R mag?
No difference... both about 100 RPM. POH says 125 or 150 IIRC.

: Verify that the prop has the correct pitch... <another biggie>
Brand new, stock 60" prop when we got it. Only 4 hours on the logbook and the
plane performs by the numbers in the POH.

So, it sounds like I probably am close to being here...
: If nothing is found above, then rig up a dial indicator and measure the
: lift on each valve, could be illuminating... I wouldn't worry about
: oil in the lifters... Just do each measurement 3 or 4 times... Call
: Lycoming, they can give you the lift specs...
: If the cam looks OK then pull the rocker arms to:
: 1. See how the bushings look.. If egg shaped you are losing lift and
: power... Don't let
: some yahoo try to tell you that the hydraulic lifters make up for this
: - they do not!
I do not recall checking the dry tappet clearance when it was assembled 3
years ago. That could be off.

: 2. see if the valves are free... WIth the rocker out of the way you can
: use a lever to
: depress each valve for sticking... The exhaust are the ones to be
: suspicious of... If any doubt rope the cylinder and remove the valve
: spring and see if the valve is free...
That's what I was thinking. Ream the guides? I still need to get ahold of SB
1425 to check the procedures... cannot seem to locate it online.

: If everything mechanical seems up to specs then squirt solvent oil down
: each valve stem and work the valve up and down (WD40, Mouse milk,
: Marvel Mystery Oil, etc.) then change oil for a fill up of lightest
: weight oil you can get < leave the filter as is> add a can of AVBLEND
: and a pint of MMO (Marvel Mystery Oil) to the fill up, and go fly the
: heck out of it for 5 hours... See if that solves it...

: denny

Thanks... will keep all posted.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Stop using MV oil and only use Shell single weight and your valve
problems will go away.

darthpup > wrote:
: Stop using MV oil and only use Shell single weight and your valve
: problems will go away.

Bzzzt....

Aeroshell 100 or 80 AD since the Aeroshell mineral oil for 25 hours on
breakin.

:)

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

wrote:
> darthpup > wrote:
> : Stop using MV oil and only use Shell single weight and your valve
> : problems will go away.
>
> Aeroshell 100 or 80 AD since the Aeroshell mineral oil for 25 hours on
> breakin.

Well, there you are. Switch to 15W50 and your problems will go away. :-)

George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.

Take a good look (or have someone take a good look) at your exhaust system. Our
Archer seemed to have lost power and kept getting worse. Everything seemed normal,
except I'd guess it was lacking 20 - 30 HP, but was using fuel at almost the
'normal' rate. We finally looked at the exhaust and found that it was coming apart
internally and some of the loose pieces were effectively blocking the exhaust flow.
Since these pieces were loose and moving around, the effect was worse at some
times than others. Had the exhaust system rebuilt and it performs as good as ever...

Mike Pvt/IFR PA28-181 at RYY


wrote:
> Hey all. Question about my Cherokee's O-360. When we first got it about 3.5
> years ago, it was very low hours SOH, but almost 10 years. We had some sticking
> valves and bad oil consumption, so sent the jugs out to have the IRAN. At that time,
> in addition to the the IRAN, a few rusted valve springs were replaced with servicable
> ones by Triad Aviation. Broke in and settled on about 1qt/8 hours on chrome jugs...
> good by all I've talked to. Ran fine, although the max static runup I'd ever seen was
> right in the midrange.... 2350 or so. Often it was on the low end... 2275-2300.
>
> For a little while now (6 months or so), it seems to have a bit of
> "mid-morning" sickness. It starts up and runs smooth and fine. Taxis smooth, runup
> good, mags fine. On the takeoff/climbout, it just doesn't "feel right." Not bad
> enough to know something's amiss, just enough to look at the VSI and say, "Hrm... I
> should be getting a little better climb than this." Usually within a minute or two of
> liftoff, it picks back up and I get an additionall 200 fpm or so. The usual
> in-flight diagnostics reveal nothing.... mixture, carb heat, mags, fuel pressure,
> CHT/EGT, etc. Runs smooth on either mag (with reduced power)... on high DA days
> leaning it a bit might be necessary, etc.
>
> Sounds a lot like a sticking valve, but I think I've done everything that can
> be done to prevent that. Baffling is in great shape. I never allow climb CHT over
> 400 or cruise over 380... and that's on the *spark-plug* CHT probes... They've been
> verified reading at 50-60 degrees hotter than the bayonet-style that Lycoming uses, so
> the CHT is actually 325-350 max. I generally cruise no higher than 65% and lean to
> about peak EGT as per Piper/Lycoming recommendations, so there shouldn't be much for
> rich combustion byproduct buildup.
>
> Other suggestions? I'm figuring to pull off the rocker-box covers, push on
> the valves, and see if I can feel friction in any of them.
>
> Thanks,
> -Cory
>

George Patterson > wrote:
: Well, there you are. Switch to 15W50 and your problems will go away. :-)

Why didn't *I* think of that? ;-)
-Cory
--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Mike H > wrote:
: Take a good look (or have someone take a good look) at your exhaust system. Our
: Archer seemed to have lost power and kept getting worse. Everything seemed normal,
: except I'd guess it was lacking 20 - 30 HP, but was using fuel at almost the
: 'normal' rate. We finally looked at the exhaust and found that it was coming apart
: internally and some of the loose pieces were effectively blocking the exhaust flow.
: Since these pieces were loose and moving around, the effect was worse at some
: times than others. Had the exhaust system rebuilt and it performs as good as ever...

: Mike Pvt/IFR PA28-181 at RYY

There's an AD against the exhaust IIRC. I know we've checked it in the past, but it has
been awhile.... worth looking into. We very well may have it off if we're messing with the
valves anyway... :)

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Is it rough running at all? or does it feel just weak in general?

Does the EGT behave normally? Your CHTs seem a little high even though
they are sparkplug versions.

Do you by chance have alcohol in your autofuel?

Do a proctology exam on the muffler.

Hmmmm.

Cory,
26" at 3500 seems a tad low.. Maybe others can chime in on this...
Cam problems can result in low manifold pressure, so the plot
thickens...

Also in case I am misreading, static RPM check R to L is done at full
throttle, not at 1800, or whatever you normally use for mag drop...
And, it will verify that the impulse pin is releasing properly if they
are similar...

Seems like you have a good grasp on engines so I don't want to keep
throwing out picky stuff... But, once you have the cowl off I would
still verify that the butterfly is not loose on the shaft and that it
opens fully...

You don't happen to have a Precise Flight vacuum system, do you?
<grasping at straws> A fine puzzle we have here... Looks like
measuring the cam is next...

Cheers ... denny

Denny > wrote:
: Cory,
: 26" at 3500 seems a tad low.. Maybe others can chime in on this...
: Cam problems can result in low manifold pressure, so the plot
: thickens...

I don't remember the altimeter setting that night, but it was pretty clear
that day. I'd think it was about 30"... at 1"/1000', that'd be 26.5" theoretical max.
The MP is measured at the intake port on #3 cylinder... losing 1/2" through the
induction system is normal AIUI.

: Also in case I am misreading, static RPM check R to L is done at full
: throttle, not at 1800, or whatever you normally use for mag drop...
: And, it will verify that the impulse pin is releasing properly if they
: are similar...
Never done a full-throttle mag check with anything in particular I was search
for other than max RPM. What would a full-throttle mag drop tell you? I don't know
of anywhere the allowable spec for that is given. The POH specifies at runup RPM, and
the TCDS specifies min/max RPM for static... but that's for both mags and mixture
leanded for DA.

: Seems like you have a good grasp on engines so I don't want to keep
: throwing out picky stuff... But, once you have the cowl off I would
: still verify that the butterfly is not loose on the shaft and that it
: opens fully...

Will do once I get the cowling off.

: You don't happen to have a Precise Flight vacuum system, do you?
: <grasping at straws> A fine puzzle we have here... Looks like
: measuring the cam is next...

I was thinking measuring the friction on the valves is probably next. With
the covers off the cam measurement may come in. I've talked with my mechanic and he's
got a jig and dial indicator rigged up to measure it. Too bad I *ALSO* need to fix
the ring gear. I won't be able to spin it up fast to get good lifter inflation.
Maybe I can hand-turn it slow enough to keep no inflation?

Thanks
-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

: You don't happen to have a Precise Flight vacuum system, do you?
: <grasping at straws>

Ooops. Nope... plain O-360-A4A.

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

nrp > wrote:
: Is it rough running at all? or does it feel just weak in general?

Not really. Possibly very slight, but in general just weak. It's kinda hard
to tell since the 4-banger always rocks and rolls a bit.

: Does the EGT behave normally? Your CHTs seem a little high even though
: they are sparkplug versions.
Again, it's a bit hard to tell on the EGT. I don't have an analyzer... just a
switched analog gauge. Last time I had time (i.e. in cruise) everything was
normal.... the EGT has a bit of a spread, but I chalk that up to a dissimilar air/fuel
ratio in the cylinders leaned for cruise.

As far as the CHT goes, when I first got the thing, I was worried about
bumping up against 400 all the time. I put a single bayonet probe in #3 and wired it
into the gauge on a switch. I verified that (at least on that cylinder) I read almost
75 degrees higher on the spark-plug probe vs. the bayonet in general. The bayonet
probe will read 300-325 in cruise at the same time the spark plug reads 375. Since
I've also got a multi-point Tannis heater, I seasonally remove the bayonet probe in
lieu of the heater for #3.

: Do you by chance have alcohol in your autofuel?

The current fuel in the tank is 100LL. I don't check every batch of autofuel,
but I generally check a sample every 4-6 months and I always get it from the same
station. Haven't found alcohol yet. When I first started running it I called the
distributor for the station and he says they never put alcohol in it.

: Do a proctology exam on the muffler.

"You will feel some slight discomfort..." :)

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

One thing - If you have a worn cam lobe, there won't be a significant
loss of power until a very substantial percentage of the lobe is worn
away. I'd think you'd see metal in the filter, too. I know of an
O-320 H engine that had a pair of intake valves that hardly moved & the
thing did seem "kinda weak", but still ran fairly smooth.

Sounds like you've covered a lot of the bases.

: Other suggestions? I'm figuring to pull off the rocker-box covers, push on
: the valves, and see if I can feel friction in any of them.

Still haven't done this (probably won't have time until the weekend). I am
trying to amass some parts to facilitate the quickie valve job. I've talked with my
mechanic and gotten ahold of SI1425 (i.e. "rope trick") and SSP1776. They *appear* to
specify the valve guide stem of 0.4985" for my O-360. SI1425 seems to give three
different reamer sizes for the nominal 1/2" size. I assume one would want to go with
the smallest (0.4985->0.4995) if possible, and only move up to the larger
(0.4995->0.5005, 0.5000->0.5010) if necessary.

I've also read that it's pretty easy to screw up the guides with the reamer,
which I would tend to agree with. They're *made* for cutting, and all I'd be trying
to do is get the carbon off. I've seen people recommend one of these:
http://tinyurl.com/bx8l3
... seems like a good way to have an adjustable, non-cutting type way to
scrape off carbon in the valve guide without taking off bronze.

I will of course be doing this with my mechanic, but I just figured I'd ask
the collective wisdom of the group on this. Good way to go?

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

I have not used the flexible cutter you listed in the URL... I have
reamed a number of valve guides over the years... My experience has
been that you will find a combination of carbon / lead salt deposits
and slight warpage (sometimes not so 'slight')... So, the straight
reamer at the nominal 0.4985" size will do the best job... It will
remove deposits and ream out the tight spots inside the bore...
Your mechanic knows best, but my suggestion is to do it by hand with a
Tee handle - and lots of muscle... The thought of using a drill motor
may be attractive, but in less than experienced hands it can wreck the
guide and then you will have to have the jug pulled and repaired...

There is still nothing stopping you from first putting solvent down the
guide bores, fresh oil, AVBLEND + MMO, and flying it... Less work and
cost than reaming the guides and doesn't do anything that can't be
undone...
Local FBO and I did this to his rental Skyhawk recently when it
suddenly stuck an exhaust valve and almost cost him a a 100 hour block
rental from customer who needed to scout a number of factory sites
across the southland over a 4 week time period, leaving the very next
morning... This was big bucks down the drain if the airplane couldn't
go the next morning...
A large spray can of WD-40 (only thing we had on hand that night) and a
quart of MMO in the oil saved him a valve job... The ol hawk came back
still humming along... Old chinese adage, "Softly, softly, catchee
monkey"..

denny

Denny > wrote:
: I have not used the flexible cutter you listed in the URL... I have
: reamed a number of valve guides over the years... My experience has
: been that you will find a combination of carbon / lead salt deposits
: and slight warpage (sometimes not so 'slight')... So, the straight
: reamer at the nominal 0.4985" size will do the best job... It will
: remove deposits and ream out the tight spots inside the bore...
: Your mechanic knows best, but my suggestion is to do it by hand with a
: Tee handle - and lots of muscle... The thought of using a drill motor
: may be attractive, but in less than experienced hands it can wreck the
: guide and then you will have to have the jug pulled and repaired...

Good to know. I will try to locate that sized reamer. I hope I can get the
stem out the bottom plug hole to clean it if it's gunked up.

: There is still nothing stopping you from first putting solvent down the
: guide bores, fresh oil, AVBLEND + MMO, and flying it... Less work and
: cost than reaming the guides and doesn't do anything that can't be
: undone...
: Local FBO and I did this to his rental Skyhawk recently when it
: suddenly stuck an exhaust valve and almost cost him a a 100 hour block
: rental from customer who needed to scout a number of factory sites
: across the southland over a 4 week time period, leaving the very next
: morning... This was big bucks down the drain if the airplane couldn't
: go the next morning...
: A large spray can of WD-40 (only thing we had on hand that night) and a
: quart of MMO in the oil saved him a valve job... The ol hawk came back
: still humming along... Old chinese adage, "Softly, softly, catchee
: monkey"..

My only thought on that is that it's an intermittent problem. Doesn't happen
repeatably, and when it does it happens to be right when there's no negotiation
allowed.... right after takeoff. Aside from a day/weekend worth of work, I'm thinking
that taking it out and cleaning it is the right way. There seems to be more than the
usual amount of OWT/circumstantial evidence supporting useage of MMO as preventative
measure. I'm generally skeptical of such snake oil, but I could see how it's possible
to help some.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

If you are using auto gas in that engine there is no way of knowing
what may be causing your valve problem. Auto gas is not refined and
adultered to any specific standard, certainly not to meet av gas
requirements. I have worked as an engineer in the petrochemical
industry and can assure you that auto gas may have any number of
additives that would cause valve problems in an av engine.

BTW -

How often do you change oil? Confirm you have a full flow filter (it
reads like you do). Does your oil filter have gray (lead) sludge in
it?

What fraction of the time since you got the engine has been 100LL vs
autofuel? I assume the autofuel has to be 91 octane autofuel to handle
your compression?

Have you ever tried to do a mag check at cruise? (i. e. could one mag
be somehow intermittent at temperature?).

Be sure to check inside the rocker covers to see if the rocker shafts
are wearing on the cover sides. I found one (but only one) in my 172M
(1700 TT over 31 years) that was worn substantially. Later shafts have
a nylon thrust boss.

You gotta post what you find. THX

Whatever you do - don't use abrasives of any sort on bronze. If you
do, it may charge the bronze with abrasive material making it into a
lap. Be careful with the reamer too.

: How often do you change oil? Confirm you have a full flow filter (it
: reads like you do). Does your oil filter have gray (lead) sludge in
: it?
Full flow filter, 50 hours, Aeroshell 80/100 depending on winter/summer. No
lead sludge in the filter, and very tiny (i.e. normal) amount of metal and carbon in
the filter and its element.

: What fraction of the time since you got the engine has been 100LL vs
: autofuel? I assume the autofuel has to be 91 octane autofuel to handle
: your compression?

93 A.K.I autofuel is used for local cruise. Generally at least 25% 100LL on
the takeoff tank. I'd say in the 3-400 hours since we've run it, probably about 60%
on autofuel.

: Have you ever tried to do a mag check at cruise? (i. e. could one mag
: be somehow intermittent at temperature?).

Done in-cruise mag checks. All fine. I generally check it along with my
leaning to verify no rough on just one mag.

: Be sure to check inside the rocker covers to see if the rocker shafts
: are wearing on the cover sides. I found one (but only one) in my 172M
: (1700 TT over 31 years) that was worn substantially. Later shafts have
: a nylon thrust boss.

Will look when I get them off. Probably take a look on Saturday.

: You gotta post what you find. THX

Will do.
-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

I just remembered a local chromed C-85 engine that would "sag" on
takeoff after an overhaul. It was supposedly traced to inadequate ring
gap. I find it hard to believe in your case though after your amount of
time since OH.

You might check the carb floatbowl fuel level with the clear flex
standpipe connected into the carb drain port method. I'm otherwise
outta ideas.....

I just remembered a local chromed C-85 engine that would "sag" on
takeoff after an overhaul. It was supposedly traced to inadequate ring
gap. I find it hard to believe in your case though after your amount of
time since OH.

You might check the carb float bowl fuel level with the clear flex
standpipe connected into the carb drain port method.

Make sure the correct rocker arms are in the correct locations. On
some Lycomings they are different for the intake & exhaust. The
exhausts have oil squirt holes in them as I recall.

I'm getting outta ideas.....

wrote:
: Other suggestions? I'm figuring to pull off the rocker-box covers, push on
: the valves, and see if I can feel friction in any of them.

Well, I got around to doing this today with my partner and mechanic. Pulled off the valve
covers and pulled off the rocker arms. Unfortunately, pressing on the valves did not reveal any
obvious sticking. Last time we did this (3 years and about 350 hours ago), you could push on the
valves and feel the ones that were sticking. Now, they all seem free.

After pulling off the exhaust and looking up in there, there was little more joy. Very
minimal deposits on the ports, bottom side of the valve, and stems. When having someone else depress
the valve and "wiggle" it side-to-side, it appeared to move some. It almost seems like the guide may
have trapezoidal holes... larger on the valve head side than on the rocker arm side of the guides.

The current plan is to get a tool to compress the valve springs so I can remove them. Maybe
I'll be able to get a better "feel" to them to see if maybe they're sticking in a certain rotation.
It'll also be necessary if I'm going to do SB388C.

Argh! I was *hoping* to find something obvious... so far, no joy. I don't see how even
with loose valve guides, the power could reduce like that. As far as I understand it, loose valve
guides *lead* to sticking valves.

Another possibility I thought of is if the holes are trapezoidal, being a bit tight on the
rocker-arm side, maybe taking off with CHT below 300 is the cause. I generally will get at least 200
CHT before departing, but try not to get over 300 to keep them from getting too hot on climbout.
Maybe the valves heat up faster than the cylinder heads and guides so they bind a little bit until
the CHT comes up and stabilizes. Seems like a long shot.

Oh, and the exhaust isn't in great shape, but I don't think it could be the problem. The
baffles are warped a bit inside, but still all in one piece.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************