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

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

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

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.

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