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stuck exhaust valve Lycoming IO-360

mjanduda

Well Known Member
Hey Builders,

I just wanted to share some pictures of an IO-360 cylinder with a stuck exhaust valve.
The cylinder was flown on a charter Cessna 172S (AVGAS only). The valve has failed well before TBO.

What do you think?
I'm not super knowledgeable about engines but for me it looks like it was flown with a very rich mixture!?

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Malte
 
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Actually it looks good. I would not have pulled the cylinder.

So what would you have done? Replacing the valve and reaming the valve guide? :)
I was a bit surprised about the valve seat. Doesn't look very good to me.

Still the question: What can you do better to prevent something like this?
 
It is a relatively standard procedure to remove the valve and ream the guide with the cyl. still installed.
My opinion is that the valve itself is probably fine (based on the carbon coloration and pattern)
Photo doesn't indicate to me anything unusual about the valve seat either. If it had a problem the carbon pattern on the valve would likely look different.
 
Actually it looks good. I would not have pulled the cylinder.

It is a relatively standard procedure to remove the valve and ream the guide with the cyl. still installed.


The bent push rod tube kinda suggests this may have been more than your average morning sickness stuck valve.

Question that comes to my poor feeble mind is when the valve is stuck tight enough to bend the pushrod and tube, should you try to repair without pulling the cylinder?
 
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I'm thinking that if it's stuck hard enough to bend the pushrod, the likelihood of getting the valve out and reaming the guide without pulling the jug is small and getting smaller...
 
I'm thinking that if it's stuck hard enough to bend the pushrod, the likelihood of getting the valve out and reaming the guide without pulling the jug is small and getting smaller...

I would pull the spring off and soak the valve guide with Hopps #9. It may loosen up the coked oil enough to knock the valve into the cylinder. Then ream and reinstall. Heating the guide area with a propane torch may also loosen it up enough to push it in.

Larry
 
A really stuck one might require a brass drift to tap it into the cylinder,but bending a pushrod is not as difficult as it might seem given their length. You can definitely ream the guide in place and even work the valve around to where you can get the stem sticking out the lower spark plug hole and clean/polish the valve stem for part of it's length. Have done it a few times on various Lycomings.
 
Carbon can stick a valve real tight.
I have seen them needing to be driven out with a hammer and brass drift punch. Reamed, and all is good.
That doesn't automatically mean that would have been successful in this case of course.... but it would have been fully worth a try.
 
seen them needing to be driven out with a hammer and brass drift punch. Reamed, and all is good

Yep, had the same happen, albeit on a O-320. Had to use a five pounder and some severe hammering to get the valve to drop in the cylinder... and the pushrod had resisted.
 
Pushrods on our engines are thin-walled to fail exactly as in this case. I would hammer the valve out of the guide with a brass drift and clean the guide with a ball hone. I do not like and do not use reamers for guides since the guides wear oblong on opposite ends imprecisely due to rocker geometry. A reamer will not clean the entire guide properly because of the wear so you're left with the possibility of sticking the valve again. FWIW I have never had any issues with any valve guide sticking again using a ball hone. Its very easy to reinsert the valve into the guide via the spark plug hole using a mechanical pickup tool and some soft rope.
 
where to find the right ball hone

Pushrods on our engines are thin-walled to fail exactly as in this case. I would hammer the valve out of the guide with a brass drift and clean the guide with a ball hone. I do not like and do not use reamers for guides since the guides wear oblong on opposite ends imprecisely due to rocker geometry. A reamer will not clean the entire guide properly because of the wear so you're left with the possibility of sticking the valve again. FWIW I have never had any issues with any valve guide sticking again using a ball hone. Its very easy to reinsert the valve into the guide via the spark plug hole using a mechanical pickup tool and some soft rope.

Hi Rocket Bob, where did you find the right size for the valve guide? Do you remember which one you use?
Thanks,
Paul
 
Thanks Rocket. That?s a must have. I had one one time that broke the push rod tube into two pieces. Apparently, it stuck, bent the push rod, broke the tube and unstuck itself! Just unbelievable.
 
With the hone, how do you go about clearing the cylinder of any remaining abrasive grit before closing it up? Just blowing air through the spark plug holes?

I'm not sure I have a warm-fuzzy feeling with that, over using a reamer slathered with grease to catch cuttings. The reamer will not release abrasive particles.
 
With the hone, how do you go about clearing the cylinder of any remaining abrasive grit before closing it up? Just blowing air through the spark plug holes?

I'm not sure I have a warm-fuzzy feeling with that, over using a reamer slathered with grease to catch cuttings. The reamer will not release abrasive particles.

Brush research hones are not like stone hones. They don't release any abrasives in the honing process. The only thing released is the carbon junk, just like a hone.
 
Guide Damage from Driving Valve Out

Be sure to file the raised ridge/burr left by the valve keepers before driving the valve from the guide. Not do so will, more than likely, damage the valve guide.

Are there oil control seals on the valve guides on these engines?
 
Be sure to file the raised ridge/burr left by the valve keepers before driving the valve from the guide. Not do so will, more than likely, damage the valve guide.

Are there oil control seals on the valve guides on these engines?

No. They have anemic oil flow to the rocker box, so no need for oil seals.
 
With the hone, how do you go about clearing the cylinder of any remaining abrasive grit before closing it up? Just blowing air through the spark plug holes?

I'm not sure I have a warm-fuzzy feeling with that, over using a reamer slathered with grease to catch cuttings. The reamer will not release abrasive particles.

I push the oiled ball hone in very slowly with the drill, take 2-3 strokes, and pull it out. Most of the trash comes out the guide at the rocker end or falls into the exhaust. On the intake side I pull the intake tube and let it fall out and its a minuscule amount.
 
Re: How do you get any particles out of the cylinder after reaming? I knew a mechanic that used shaving cream, Foamy. He would spray some thru the spark plug hole, do the reaming, then vacuum out the shaving cream. Said he had learned the trick in A&P school years back. Dan from Reno
 
Grit

With the hone, how do you go about clearing the cylinder of any remaining abrasive grit before closing it up? Just blowing air through the spark plug holes?

I'm not sure I have a warm-fuzzy feeling with that, over using a reamer slathered with grease to catch cuttings. The reamer will not release abrasive particles.

Since the valve guides stop inside the ports and don't extend into the cylinders, debris that falls out of the inner end of the guides will end up in the ports and not the cylinder. if the intake and exhaust pipes are removed prior to reaming, it should be pretty easy to keep the debris out of the cylinder itself.

Skylor
 
Stuck exhaust valve Lycoming

So what does it mean when you're in cruise, leaned but ROP, everything looks good but one cylinder, number three, is running lower egt then the rest. By almost a hundred degrees.
 
So what does it mean when you're in cruise, leaned but ROP, everything looks good but one cylinder, number three, is running lower egt then the rest. By almost a hundred degrees.

Based on that data alone, almost nothing.

EGT absolute temperatures are not of much value. The key with the EGT is where they peak versus fuel flow - that will tell you ROP or LOP on each individual cylinder, and those will likely be a different fuel flows for each cylinder (at least before starting to make adjustments). To really know what is going on with your engine, you need an accurate fuel flow meter, and CHT/EGT measurements on each cylinder. Fuel injection is also helpful versus carbureted, but not required.
 
So what does it mean when you're in cruise, leaned but ROP, everything looks good but one cylinder, number three, is running lower egt then the rest. By almost a hundred degrees.

Assuming it is running 100 less than normally seen, It could be 100* richer or 100+* leaner. Latter is more likely. LOP should be confirmed by seeing CHT on that Cyl 10+ degrees cooler than normal. If that is the case, look for a plugged injector for FI or an intake leak on a carb. A stuck valve likely cause rough running and CHT's would fall sharply.

Larry
 
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We dropped the exhaust valve, honed the guide, lapped the valve face and the compression went up to 76/80 (previously 66/80). Flew a couple times since and plan another compression test soon. EGT temp is still a bit lower than the others so I?ll investigate that as well.
 
More details on honing valve guide, please

Hello - During installation of my Mag after IRAN, I discovered my #1 cyl. had no compression - 05/80 (cold), and you could hear the air coming out the exhaust. I borescoped the cyl, valves looked ok. Short ground run of engine, CHT and EGT all came up together. #1 was back up 72/80 hot. Next day, checked #1 cold - no compression again. My A&P that does my CI, wants to pull the cyl and send it off for repair. I am thinking I should try honing the exhaust guide first.
Those of you that have honed, would you please give more details of the honing process? RocketBob mentioned using oil - just engine oil, or? Should I do anything to the valve itself to remove the build up on the stem?
Thank you for the response -
 
Tim,
I don't think I'd jump right to pulling the cylinder, yet that may indeed be the path you end up on either way. I don't think honing is step 1 either.

I would say that step 1 is to get a borescope in there and look at the valve closely, followed by step 2 getting the proper wobble test fixture and checking that out. The valve could have worn guides, and not seat properly, and if it's a loose valve, no amount of honing the guide is going to fix it. So really your job right now is to determine exactly what the issue is, and that is something best done with a borescope and wobble test. If the guide is worn, or valve is burned, yeah, you'll probably be pulling the cylinder anyway, but making that determination is worth doing before you start loosening the cylinder bolts.

The compressions you quoted were low enough that personally I would expect you have worn guides, and the valve isn't seating well. If the wobble test turns out good though, you probably could try just lapping the valve first, and that may bring it back.
 
I have used a 40 caliber (I think that was the size; maybe .45) gun barrel cleaning brush as well. That seems to work well and not mess with a guide as the brush is brass.... Doing the old Rope Trick to drop the valve out. I have heard of mechanics pressurizing the cylinder with LOW pressure from a compression tester with the intake valve closed, the exhaust port plugged (shop rag) and the other spark plug hole plugged up to keep debris out of the cylinder. Note: LOW pressure; it can still move a prop if it is too high. Just enough to get air flowing out of the guide.
 
Fix

In my experience, good operating practices (follow Lycoming engine operators manual, not what you heard or read on the internet) and compliance with Lycoming SB 388 & SI 1485 fixes the "problem" with stuck valves. Russ
 
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In flight stuck exhaust valve

A number of posts about stuck valves, but no mention of when the valve stuck. My experience with four low time 7 to 1 comp. Continental Titan cylinders on O320 E2A has been pretty scary.

First forced landing at about 380 hours since new cylinder due to stuck valve on #1 level at about 15 minutes into the flight. All AvGas used prior.

Second forced landing yesterday at about 435 hours since new cylinder due to stuck valve on #4 about 50 minutes into the flight. Non-Ethanol 90 with MMO used for last 55 hours.


Flights were at 50 to 55% power, cyl head temps around 300* No morning sickness, nary a clue prior to cylinder dropping out in level flight and heavy vibration. About 10 minutes on three cylinders to landing.

Plan is to ream all four exhaust valve guides.
 

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In my experience, good operating practices (follow Lycoming engine operators manual, not what you heard or read on the internet) and compliance with Lycoming SB 388 & SI 1485 fixes the "problem" with stuck valves. Russ

I totally agree! In fact the SB is mandatory and was issued to prevent the sticking problems which may occur near the 400hr point. It is a routine procedure that has been in the operators manual since certification. IDK why we don't embrace it just like changing oil? The only reason the 400hr maintenance check became an eventual SB is because owners were not doing it, so Lycoming had to speak louder. SI 1585 allows relief from 400 hr intervals to 1000hrs intervals if the improved valve guides are installed.

I do not like spending money on maintenance anymore than the next guy, and ya we're experimental and we don't have to, but it is still i your best interest to do so. What was the motto - "Pay me now or pay me latter"

https://www.lycoming.com/sites/defa...termine Exhaust Value and Guide Condition.pdf

https://www.lycoming.com/sites/default/files/Exhaust Valve and Guide Identification Procedure.pdf
 
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Thank you for the responses

Thank you all, for the comments and links. I am going to hone or ream and do the wobble test - later this week or next (supplies are on order). I will post what I find when complete.
Thank you again -
 
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