o-200 stick valve ?

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bobkiksass

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bobkiksass
o-200 sticky valve ?

I have a cessna 150 with continental o-200.

My plane had been running a bit funny a while back, so my mechanic had advised to have the mags & carb overhauled due to their age an condition. After doing that, the plane seemed to run better, but we were still experiencing a bit of "morning sickness" . Basically when the motor is idling under 1000 rpm, u can hear it kind of skip a beat or make a really light thud noise.

I guess when he test ran it, he noticed one of the cylinders wasnt as hot as the rest. He advised to borescope the cylinders to see if there was any sign of the valve not working properly. When he inspected it, it looked fine, and he suggested one of the valves could "just be a bit sticky." But he suggested it wasnt something to be concerned with since the plane seemed to run well when up at power.

This was about 8-10hrs ago of running the motor on the plane.
I am still experiencing this weird "morning sickness" and am somewhat concerned that it could be a sign of something else being a problem, when we had done oil analysis the aluminum was somewhat higher than it should be. The mechanic thought that the aluminum was from the carb having a loose butterfly that moved side to side. The motor does run great when not at idle now. Only other thing I notice is that the rpm gauge bounces just slightly, maybe 50 rpm when cruising around 2400-2500 rpm.

For all the mechanics here, would you suggest having a second mechanic check out the motor ? Is valve stickiness a problem if the plane runs fine when the throttle is up and going ? Are there any additives to help burn the sludge up sticking the valves ? I want to protect the investment on this baby, and am worried running it with sticky valve may be asking for trouble.
 
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The stupid easy check that can cause similar symptoms (miss at low power) is to pressurize the induction system and check for leaks with soapy water.


If you do have a sticky valve it may be possible to correct it by reaming the valve guide, and this can actually be done with the cylinder in place.


Also, bouncy tach isn't uncommon, maybe lube the cable.
 
A valve that's sticking when cold is liable to foul further and end up sticking in flight and costing a bunch of power. If it sticks hard enough it will buckle the valve pushrod.
 
Hi Bob. It sounds to me like it could be a valve stem with carbon buildup. Or, it could just be an oily bottom plug. I have a C-150 that has had an exhaust valve stick twice. Both times, it stuck before I took off and the engine wasn't just a little rough, it was terrible. Since your mechanic inspected it and said the valve was working properly, it could be a plug. Our C-150 doesn't, but we had a C-172 that was rough like that almost every time we flew. When it is rough next time when you do your runup, lean out the mixture and run the engine at 2,000 rpm or so for about a minute. If that clears up the problem, it is probably a plug fowling out. I use TCP in our C-150 religiously to hold down the carbon buildup. It seems to help a lot.
 
Pull your rocker box covers and check for something like this.
 

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When the engine is cold the clearances are tight and if the valve guide has lead or carbon build up, the valve will fail to open and close fully. As the engine heats up, the clearances loosen up and the roughness seems to disappear. Your engine is telling you that now is the time to fix it before the valve sticks for good and you lose that cylinder. Ignore it at your own risk. It will only get worse. The valve stem and guide can be cleaned without pulling the cylinder now but if you wait and the valve sticks hard, you'll probably have to pull the cylinder to unstick it. If you're lucky it will have stuck open, if it were to stick closed, things will bend/break and it could be very expensive cleaning out all the bits of metal that will end up throughout the engine.
 
Witmo said:
When the engine is cold the clearances are tight and if the valve guide has lead or carbon build up, the valve will fail to open and close fully. As the engine heats up, the clearances loosen up and the roughness seems to disappear. Your engine is telling you that now is the time to fix it before the valve sticks for good and you lose that cylinder. Ignore it at your own risk. It will only get worse. The valve stem and guide can be cleaned without pulling the cylinder now but if you wait and the valve sticks hard, you'll probably have to pull the cylinder to unstick it. If you're lucky it will have stuck open, if it were to stick closed, things will bend/break and it could be very expensive cleaning out all the bits of metal that will end up throughout the engine.
Click to expand...

If it sticks open,, you can buy a new piston too.
 
When the engine is cold the clearances are tight and if the valve guide has lead or carbon build up, the valve will fail to open and close fully.
Click to expand...

Tim, wouldn't the borescope examination have shown the valve not seating fully?
 
Sounds like you'd better get it fixed, Bob. Could get a lot more expensive.
 
Tom-D said:
If it sticks open,, you can buy a new piston too.
Click to expand...

I thought the O-200 valves are non-interference and an open would only result in loss of power on that cylinder?

Just wondering... I don't own one...
 
denverpilot said:
I thought the O-200 valves are non-interference and an open would only result in loss of power on that cylinder?

Just wondering... I don't own one...
Click to expand...
Where did you hear that.??
 
A friend just had this issue with his 140. I watched a mechanic do all 4 cylinders, he made it look easy. So basically you might want to find a mechanic that has done this a few times and I am sure you will be back flying soon.
 
Re: o-200 sticky valve ?

bobkiksass said:
I have a cessna 150 with continental o-200.

My plane had been running a bit funny a while back, so my mechanic had advised to have the mags & carb overhauled due to their age an condition. After doing that, the plane seemed to run better, but we were still experiencing a bit of "morning sickness" . Basically when the motor is idling under 1000 rpm, u can hear it kind of skip a beat or make a really light thud noise.

I guess when he test ran it, he noticed one of the cylinders wasnt as hot as the rest. He advised to borescope the cylinders to see if there was any sign of the valve not working properly. When he inspected it, it looked fine, and he suggested one of the valves could "just be a bit sticky." But he suggested it wasnt something to be concerned with since the plane seemed to run well when up at power.

This was about 8-10hrs ago of running the motor on the plane.
I am still experiencing this weird "morning sickness" and am somewhat concerned that it could be a sign of something else being a problem, when we had done oil analysis the aluminum was somewhat higher than it should be. The mechanic thought that the aluminum was from the carb having a loose butterfly that moved side to side. The motor does run great when not at idle now. Only other thing I notice is that the rpm gauge bounces just slightly, maybe 50 rpm when cruising around 2400-2500 rpm.

For all the mechanics here, would you suggest having a second mechanic check out the motor ? Is valve stickiness a problem if the plane runs fine when the throttle is up and going ? Are there any additives to help burn the sludge up sticking the valves ? I want to protect the investment on this baby, and am worried running it with sticky valve may be asking for trouble.
Click to expand...

How much time on the engine ?

What is the carb P/N ?

What cylinders are installed?
 
Engine has roughly 330 hrs on it, it is penn yann factory rebuild.

PN: 10-4894-1 for the carb, was just overhauled by aircraft accessories.

mags were just overhauled as well by aero accessories.

prop was recently removed and overhauled as well

tytan eci cylinders
 
bobkiksass said:
Engine has roughly 330 hrs on it, it is penn yann factory rebuild.

PN: 10-4894-1 for the carb, was just overhauled by aircraft accessories.

mags were just overhauled as well by aero accessories.

prop was recently removed and overhauled as well

tytan eci cylinders
Click to expand...

When were the plugs last cleaned?

What is your idle mixture rise?
 
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Plugs cleaned and gapped 8 hrs ago on motor. Don't know what idle mix rise is or how to find that.
 
bobkiksass said:
Plugs cleaned and gapped 8 hrs ago on motor. Don't know what idle mix rise is or how to find that.
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How much does the RPM rise when you pull the mixture all the way out. = Idle mixture check 10-50 RPM rise is the correct amount.
 
Tom-D said:
If it sticks open,, you can buy a new piston too.
Click to expand...

If it beats a hole in the piston, then you have to worry where all those metal bits and pieces get carried throughout the engine.
 
Witmo said:
If it beats a hole in the piston, then you have to worry where all those metal bits and pieces get carried throughout the engine.
Click to expand...

That's right, it never gets better with out doing a repair, but the debris from the combustion chamber goes out the exhaust valve. and if the piston totally destroyed you will know about it soon enough.

But in this case I don't think it is a valve problem, because that would effect the engine at all power settings.
 
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Tom-D said:
That's right, it never gets better with out doing a repair, but the debris from the combustion chamber goes out the exhaust valve. and if the piston totally destroyed you will know about it soon enough.

But in this case I don't think it is a valve problem, because that would effect the engine at all power settings.
Click to expand...

I'm not convinced either. Could be the culprit, could not.
 
TOM-D ; I havnt tested to see what the rpm rise is on mixture cutoff. But before the carb was overhauled, there was no rpm rise on mix cutoff. Now there is a good bit, I havnt been out at the plane in a few days, but will check on next flight. Im guessing it is more than the 10-50 rpm range.

It did seem to me like the motor was running richer than it used to, just based on smelling it on engine start. Can you explain how the mixture rise could be causing this roughness at idle, are you thinking its too rich and fouling out the plugs ?

Before I had the carb and mags overhauled, it would produce a power loss (200 rpm or so) and engine roughness at full throttle randomly on takeoff, and that was the reason I had these accessories overhauled. If I lowered the nose and pulled power back it would stop the problem. Mechanic thought it was the mags and carb causing this. I havnt experienced this roughness at full throttle since these parts have been overhauled.

Thanks for the advice
 
Idle mixture may be set to rich. The key is to slowly bring the mixture to cut off, yanking it back can mask the problem.
 
can you explain what you mean by "The key is to slowly bring the mixture to cut off, yanking it back can mask the problem" . Is that just to determine what the mixture cut off rise is ? Should I try to run the motor to clear fouled plugs on next run up ? Should that fix the problem ? On last oil analysis the lead was really high, but the mechanic thought the plugs looked good and were not showing excess gunk, showed a clean burn.
 
When you next run the plane, set the RPM to 1700 or higher for a few seconds to clear it out,

Then set the throttle to idle, record the RPM

Slowly bring the mixture to cut off, watching the RPM, it should rise slightly before falling off and shutting down. Record the amount of that rise.


Lead is alway high on planes running 100LL
 
A sticking valve is most likely going to show up on a compression test long before you're going to be able to see anything with a borescope. When the valve does indeed stick there's going to be no doubt in your mind that you have lost a cylinder. Hopefully it won't happen during takeoff on a hot day because you're going to lose a lot of power and it'll be rough as a cob.

Gauging your cut-off rise with a bouncy tach needle might not be easy, it's barely perceptible when set correctly but if you're not getting any or the rise is around 100 rpm then you need to adjust the idle mixture screw - the big knurled one at the throat. That's not going to have any effect on your normal open throttle operating ranges however.
 
all cylinders 78 + / 80. motor has really good compression
 
got out to fly the plane today,

wire harness was not changed with mags
when the motor is cold, the motor runs like its lugging with closed idle around 650 rpm
usually when cold I give it a bit of throttle to get it to run smooth till warmed up
when the motor is warmed up it idles smooth at around 650 rpm with closed throttle

upon testing the mixture cutoff, with motor warm and throttle closed, I slowly backed out mixture. at about 50-75% mixture cutoff, the motor runs much smoother and i get like 750 rpm, pull it all the way to 100% cutoff and it peaks up to 900-1000 before dying. It seemed to run a lot better with the mixture way out.

I assume the idle mixture is set too rich, is there any danger to running the plane this way before I get the mechanic to adjust it ?
 
Would a leaking primer cause these weird issues? Easy enough to cap it off and see.
 
You are indeed running way rich, Bock's suggestion of checking the primer isn't a bad one
 
bobkiksass said:
got out to fly the plane today,

wire harness was not changed with mags
when the motor is cold, the motor runs like its lugging with closed idle around 650 rpm
usually when cold I give it a bit of throttle to get it to run smooth till warmed up
when the motor is warmed up it idles smooth at around 650 rpm with closed throttle

upon testing the mixture cutoff, with motor warm and throttle closed, I slowly backed out mixture. at about 50-75% mixture cutoff, the motor runs much smoother and i get like 750 rpm, pull it all the way to 100% cutoff and it peaks up to 900-1000 before dying. It seemed to run a lot better with the mixture way out.

I assume the idle mixture is set too rich, is there any danger to running the plane this way before I get the mechanic to adjust it ?
Click to expand...


This is very typical of the new rebuilt carbs on the 0-200, they run too rich.
running that way will foul plugs quickly.

turn the idle mixture knob about 2 turns to the (L) side it is marked.

what is your cruise fuel flow?
 
Not my post, but I just wanted to thank Tom and others here for sharing their knowledge. And no charge, no less! Thanks guys.
 
I was flying the plane yesterday with the FAA examiner, getting ready to take my PPL test here in next few weeks.

We were climbing out after talking for a good bit with the plane idling on the ground. I told him I thought the carb is running too rich, so we leaned it out while idling on the ground. After we took off and started climbing out at full rich, the motor stumbled a bit. The examiner had me under the hood tracking a vor. He instantly grabbed the mixture and leaned it out, the stumble stopped.

It got both of our hearts racing a bit, but he seemed to think its just the carb isn't adjusted right. A few more times we encountered a bit of stumble, and really had to focus on keeping the mixture leaned out. He said with mixture too rich it will just temporarily fowl out a plug.

We landed did a mag check, it seemed to run fine on the ground. It was weird the examiner did a check where he slowly backed out the mixture with the throttle at idle. When he did it we didn't get much of a rise in the RPM as I had when I tried it before. He said he thought it was the mixture causing the stumble in the motor, but didn't really see a big rise when testing the idle mixture cutoff so that meant its not running too rich in his mind. Its weird it seems to be a bit of intermittent problem. Perhaps there is a problem with the primer as has been suggested ?

I can tell it runs really rich just from the smell the motor makes when starting it since overhauling the carb.

I don't think Im going to fly it again until I get a mechanic to tune the carb.

thanks for your guys advice
 
bobkiksass said:
I was flying the plane yesterday with the FAA examiner, getting ready to take my PPL test here in next few weeks.

We were climbing out after talking for a good bit with the plane idling on the ground. I told him I thought the carb is running too rich, so we leaned it out while idling on the ground. After we took off and started climbing out at full rich, the motor stumbled a bit. The examiner had me under the hood tracking a vor. He instantly grabbed the mixture and leaned it out, the stumble stopped.

It got both of our hearts racing a bit, but he seemed to think its just the carb isn't adjusted right. A few more times we encountered a bit of stumble, and really had to focus on keeping the mixture leaned out. He said with mixture too rich it will just temporarily fowl out a plug.

We landed did a mag check, it seemed to run fine on the ground. It was weird the examiner did a check where he slowly backed out the mixture with the throttle at idle. When he did it we didn't get much of a rise in the RPM as I had when I tried it before. He said he thought it was the mixture causing the stumble in the motor, but didn't really see a big rise when testing the idle mixture cutoff so that meant its not running too rich in his mind. Its weird it seems to be a bit of intermittent problem. Perhaps there is a problem with the primer as has been suggested ?

I can tell it runs really rich just from the smell the motor makes when starting it since overhauling the carb.

I don't think Im going to fly it again until I get a mechanic to tune the carb.

thanks for your guys advice
Click to expand...


Stumbled climing full rich? Like as throttle was applied to full power or after throttle was at full power for say 120 seconds?

What was the outside air temp? What's your field elevation? If your hot & high it's not going to run well at full rich anyways, meaning you must lean it. When the outside air temp falls or you move to an airport with lower field elevation the engine runs leaner at the same setting (full rich).
 
we are at sea level, it was in the mid to high 70s yesterday, warm but not too hot. Humidity was somewhat high.

we had been climbing out for about 3-4 minutes when it stumbled.

I thought you normally climbed out with full rich, but examiner suggested its not bad idea to lean as your climbing out. I learn something every day
 
Can't adjust that,

Sounds like it is jetted wrong.

After departing a SL airport and climbing at loaded 150 rates for just a few minutes you shouldn't have to lean the mixture
 
Skylane81E said:
Can't adjust that,

Sounds like it is jetted wrong.

After departing a SL airport and climbing at loaded 150 rates for just a few minutes you shouldn't have to lean the mixture
Click to expand...


Jette wrong or float level too high or the primer is leaking as suggested (seems unlikely its the primer)
 
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