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Sticking Lycoming O-360 valve again?



 
 
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  #1  
Old January 16th 06, 03:40 PM posted to rec.aviation.owning
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Default Sticking Lycoming O-360 valve again?

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 *
************************************************** ***********************

  #2  
Old January 16th 06, 04:57 PM posted to rec.aviation.owning
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Default Sticking Lycoming O-360 valve again?

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

  #3  
Old January 16th 06, 05:05 PM posted to rec.aviation.owning
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Default Sticking Lycoming O-360 valve again?

: 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 *
************************************************** ***********************

  #4  
Old January 16th 06, 05:16 PM posted to rec.aviation.owning
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Posts: n/a
Default Sticking Lycoming O-360 valve again?

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

  #5  
Old January 16th 06, 06:11 PM posted to rec.aviation.owning
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Posts: n/a
Default Sticking Lycoming O-360 valve again?

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.
  #6  
Old January 16th 06, 07:15 PM posted to rec.aviation.owning
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Default Sticking Lycoming O-360 valve again?

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

  #8  
Old January 16th 06, 08:18 PM posted to rec.aviation.owning
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Posts: n/a
Default Sticking Lycoming O-360 valve again?

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 *
************************************************** ***********************

  #9  
Old January 16th 06, 08:19 PM posted to rec.aviation.owning
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Posts: n/a
Default Sticking Lycoming O-360 valve again?

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 *
************************************************** ***********************

  #10  
Old January 16th 06, 08:32 PM posted to rec.aviation.owning
external usenet poster
 
Posts: n/a
Default Sticking Lycoming O-360 valve again?

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 *
************************************************** ***********************

 




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