Sticky valve_Lycoming IO-360-A3B6D

[cujet]

Theory has it that... When new guides are installed the only thing holding them in place is the negative or press fit in the head. Over a few hundred hours of heat and cool cycles the metals equalizes their pressure against each other and  the head squeezes the guide to a smaller dia.  

 

 My Lyc IO-360 just stuck a #2 ex valve at 7500 feet, top of descent. 320 hours since overhaul. What's interesting about this is the fact that I did the overhaul, and documented every measurement. The valve to stem clearance DID tighten up considerably and the result was a valve guide with 0.001 inches LESS clearance than before, in the section nearest the port and a bit tighter than the initial ream elsewhere. Likely it happened in the way you describe. The aircraft is flown often, and oil change intervals never exceed 25 hours. The cylinders had 1700 hours since new, 320 since overhaul, and new valves and guides were installed at overhaul. 

 

Of course, the sticking valve happened as I reduced power a bit, and headed downhill, picking up a good bit of speed and cooling air. It went away with reduced RPM. Never had any "morning sickness" or any other form of roughness. This was the first indication there was a problem. 

 

During the repair and rework yesterday, after hammering the valve free from the guide, I used the very same reamer on the valve guide that I did initially, and it removed metal. I would guess that the thermal distortion has run it's course, and the repair will be a final fix on my cylinder. 

 

The other cylinders "wobble checked" just fine. 

 

As another data point, our company's Extra 300L, with a Lyc IO-540 angle valve, with just over 100 hours since new, stuck a #5 exhaust valve. I don't fly that aircraft. I do maintain it, and I do use a different oil in that engine than mine. It gets very frequent oil changes. 

 

Edited for clarity. I did not mean to say the valve stem to guide clearance had been reduced to 0.001 inches. Only that it was about 0.001 inches tighter in one small section of the guide, nearest the port/guide interface. 

[mcpilot]

This is interesting.  Do you run LOP?  What type of power setting do you use and where in reference to peak EGT do yo lean to?

 

If we can gather some data together and find a pattern we can make these stuck valve issues go away....  

[mcpilot]

Just curious.. Do you you use an engine monitor?

 

 

 My Lyc IO-360 just stuck a #2 ex valve at 7500 feet, top of descent. 320 hours since overhaul. What's interesting about this is the fact that I did the overhaul, and documented every measurement. The valve to stem clearance DID tighten up considerably and the result was a valve guide with 0.001 inches clearance in the section nearest the port and a bit tighter than the initial ream elsewhere. Likely it happened in the way you describe. The aircraft is flown often, and oil change intervals never exceed 25 hours. The cylinders had 1700 hours since new, 320 since overhaul, and new valves and guides were installed at overhaul. 

 

Of course, the sticking valve happened as I reduced power a bit, and headed downhill, picking up a good bit of speed and cooling air. It went away with reduced RPM. Never had any "morning sickness" or any other form of roughness. This was the first indication there was a problem. 

 

During the repair and rework yesterday, after hammering the valve free from the guide, I used the very same reamer on the valve guide that I did initially, and it removed metal. I would guess that the thermal distortion has run it's course, and the repair will be a final fix on my cylinder. 

 

The other cylinders "wobble checked" just fine. 

 

As another data point, our company's Extra 300L, with a Lyc IO-540 angle valve, with just over 100 hours since new, stuck a #5 exhaust valve. I don't fly that aircraft. I do maintain it, and I do use a different oil in that engine than mine. It gets very frequent oil changes. 

[bnicolette]

And we're you using any fuel/oil additives?

[N201MKTurbo]

Time for a poll

 

Everyone who ever had a stuck valve.

 

Were you using Cam Guard?

 

Were you running LOP?

[aaronk25]

After my installation of the airwolf oil seperator, I now wipe down the belly after a couple fights with some cleaner wax. It's amazing how much SOOT there is on the transponder antenna directly behind the exhaust pipe all the way back to the tail. If you wipe a finger on it the soot is noticeable.

After I get to 700agl I go LOP to 11.5-10.5gph and it's still amazes me how dirty these engines are. All that crap coming out of the cylinders no doubt collects on the valve stems.

[jetdriven]

Time for a poll

 

Everyone who ever had a stuck valve.

 

Were you using Cam Guard?

 

Were you running LOP?

 

I would wager a guess that high CHT's coke the oil in the valve stem and cause the valve to stick. Another thing is that some Lycoming lifters don't pump enough oil into the head to properly cool the exhaust valve.  Cranking up the oil pressure can help with this.  here's an article that describes some of that.     

http://www.airplanebroker.com/MARV.HTM

 

FWIW our factory engine runs about 95 PSI in cruise and I dont intend to change it.

[carusoam]

I would have thought increasing the oil pressure would force it to leak out of the system more than before. Apparently that doesn't happen...

Best regards,

-a-

[rbridges]

All of us should have engine analyzers IMO.  They offer so much capability relative to the cost that it should be a no-brainer.  In fact, if you disagree with that assessment, I would go so far as to say that you likely don't understand how to actually *use* one!  There are used EDM-700s turning over on the secondary market now for very modest money, and an enterprising owner can install the probes under supervision to keep the costs down as it is simple work, just tedious.

 

My own personal story about the discrete benefit of having one revolves around a faulty Champion plug a couple years ago... I stopped for cheap fuel on my way home one afternoon, After restarting, the EDM-700 showed a high EGT on one cylinder, and doing a mag check confirmed a dead plug.  Luckily there was a mechanic still working, and he loaned me a screwdriver and wrenches to remove the cowling and plug, and then he tested the plug to confirm it's condition.  He then sold me a plug that he fortunately had on the shelf, and I was on my way with only a 30 minute delay vs. who-knows-how long it would've taken to determine what was causing the roughness on a mag check prior to takeoff.  (spare plugs and tools went into my baggage kit after this episode)

 

I had a similar issue with a bad plug.  Engine analyzer (UBG16) showed me that temps dropped in the #2 cylinder when I switched to the right mag.  It made diagnosing the problem very easy.

[cujet]

This is interesting.  Do you run LOP?  What type of power setting do you use and where in reference to peak EGT do yo lean to?

 

If we can gather some data together and find a pattern we can make these stuck valve issues go away....  

 I generally don't run lean of peak. I like the speed, so I run a bit rich of peak. My GEM engine monitor is older and does not display the actual EGT. Only the trend and comparison between cylinders. In fact, the display is adjustable so the bar graph is pilot friendly. 

 

I had been operating at 2600RPM, 7500 feet

 

I was using AS-100 oil, with Camguard, it had 23 hours on the oil. 

[Jsavage3]

A sticky valve update...and important follow-up information that I was just made privy too...

So, it's been 85 flight hours since my first bout with the sticky valve and everything ran along just perfectly since then until about two weeks ago when I had those same indications again one cold morning...shucks!  Now what?  Well, it was approaching annual time, so I informed my shop of my sticky valve history from 85 hours ago and the current indications and asked for advice.  They contacted their engine guy who immediately thought it was an exhaust valve guide diameter issue as he has seen this before (as have I, said I).  The engine guy found cylinder 1 had a sticky exhaust valve and this, he said, was the source of my latest sticky valve indications.  He reamed it IAW the Lycoming SB.  Cylinder 2 was the one that gave me issues 85 hours ago and it was of the proper size as he checked that one too.  In addition, he checked cylinders 3 & 4.  So, although I have not been able to run it yet (as it's in the middle of its annual), the engine guy says with confidence that my problems are now fixed.  Sigh of relief from me!

If you're having sticky valve indications, I would like to suggest that you have your valve guide dimensions checked and ensure they are of the proper size for your specific engine.

Edited January 12, 2016 by Jsavage3

[carusoam]

Nice follow-up JS.

Best regards,

-a-

[aaronk25]

That will help a few people for sure.