Valve Guides and Lycoming Engines

While doing the annual inspection on SJ's Super Cub I have run into a snag. SJ is kinda hard on stuff but the O-360-C1G that was installed new when the airplane was built has 1200 hrs on it and has performed flawlessly as long as I have been maintaining it. Normally I check compression, clean plugs, timing oil etc. However this year the normal 77 and 78/80 compressions were not to be on #3. Working at it I could get 70/80 but the disturbing thing was the rush of air I could hear rushing out of the exhaust pipe. Over the years I have had a few low cylinders that acted this way and they came back up after a short run. Unfortunately this one didn't come up after a short run, short flight, 45 minute flight or stacking the valve, it actually went down to 62/80 still pouring out the exhaust pipe. Borescope showed nothing abnormal but when I pulled out the old wobble test fixture it was obvious we had a worn exhaust valve guide. I then decided to check the other three cylinders and low and behold they were all worn, one not so bad but three of them were way out of tolerance. It used to be recommended to do the wobble test on Lycoming engines every 400 hours via Lycoming Service Bulletin 388C however when they came out with the new "HiChrome" guides in 1996 that inspection went to 1000 hrs per Service Instruction 1485A. SJ's cylinders do have the "HiChrome" guides as verified by the "C" stamped on the cylinder heads but why the abnormal wear? Lycoming didn't have an answer. They did want to know what the normal CHT's were which in this case is only known on one cylinder and rarely sees 370 but usually runs 325 or so which is well below the 435 degree redline for this engine. Some internet research shows that some turbo charged Mooney's have external oil lines feeding the exhaust valve guides and that Cessna moved the oil pressure pickup point (reads midway down the oil flow path instead of off the oil pump) and upped the redline on oil pressure on the new 172, 182 and 206. So is it CHT temps, lack of oil, or what. I am baffled at this point. I have all cylinders off and guides removed. Waiting on new guides to arrive so I can install and grind the valves and seats. I will definitely be doing the wobble test religiously and make notes of the clearances to get an idea of any wear patterns. Just wondering if anyone else has had issues or experiences with this problem?

You can even see the wear as I push the valve two different directions.

I had stopped in at Graham that very day and the first one off was really wobbly, so much so that even my lack of finely tuned mechanical skills said... “WOW, that can’t be good.” Steve was careful to explain what I was seeing and all educating me beyond my ability... all the while I was saying to myself "hope there won't be a quiz!"

Now at this point I feel it important to give Steve much credit as my presence in Graham that day presented a significant opportunity in the way of some photos of my (former) burnt offering cylinder(s) still on my phone that could have been easily sent to SJ as a progress report... you know just to share the love so to speak. But Mr. Pierce with his always known high mechanical standards and now duly noted equally high moral standards would have none of it...

What’s and Okie to do.

OC

Steve,

Were any of the guides loose in the cylinder?

Tim

That happens to Continental O-200s also. Like yours they get quite worn before the compression goes south. I assumed it was soft guides, poor lubrication, or a just poor design. It seems like everybody around here just lives with it. It looks like the friction of the rocker on the valve stem, as it rocks the geometry pushes and pulls the valve, and causes the wear. If only there were roller rockers for airplane engines. Could it be a fuel problem?? Clyde Wittenbrook at Barnesville, Oh claimed the 100 LL changed a couple of years ago. He said it doesn't store as well as it used to. Something about the aeromatics being different. I thought he was just being cranky because he doesn't sell much fuel. If the formulation did change, what else might be different?? Could this be a fuel related problem? jrh

OLDCROWE said:

Now at this point I feel it important to give Steve much credit as my presence in Graham that day presented a significant opportunity in the way of some photos of my (former) burnt offering cylinder(s) still on my phone that could have been easily sent to SJ as a progress report... you know just to share the love so to speak. But Mr. Pierce with his always known high mechanical standards and now duly noted equally high moral standards would have none of it...

What’s and Okie to do.

OC

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You Okie's can play those practical jokes and one another but sooner or later it's gonna blow up in your face. I have enough stuff blow up in my face to intentionally initiate. 8)

behindpropellers said:

Steve,

Were any of the guides loose in the cylinder?

Tim

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No, they were nice and tight. Good interference fit.

N86250 said:

That happens to Continental O-200s also. Like yours they get quite worn before the compression goes south. I assumed it was soft guides, poor lubrication, or a just poor design. It seems like everybody around here just lives with it. It looks like the friction of the rocker on the valve stem, as it rocks the geometry pushes and pulls the valve, and causes the wear. If only there were roller rockers for airplane engines. Could it be a fuel problem?? Clyde Wittenbrook at Barnesville, Oh claimed the 100 LL changed a couple of years ago. He said it doesn't store as well as it used to. Something about the aeromatics being different. I thought he was just being cranky because he doesn't sell much fuel. If the formulation did change, what else might be different?? Could this be a fuel related problem? jrh

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I have had the opposite problem with the O-200 and even some Lycomings. This engine has had a straight diet of 100LL as far as I know and gets flown pretty regularly.

Are the exhaust valves used in these engines sodium filled? If you can grind them then I doubt it but it is amazing the amount of heat those things have to transfer through the guides so once they start wearing at all it's an "avalanche" breakdown from there (at least on motorcycle engines). SJ is lucky it didn't break and drop into the cylinder.

Steve are you going to replace all the valves that were in "wobbly" guides just under the assumption they may have been heated past their "redline" despite what the instruments said about the overall engine temperature? Just wondering. In my Honda dealership my mechanics always replaced any valve from a high performance DOHC engine that came out of a worn guide just because of the worry that the metallurgy of the valve might have been compromised and if one let go at 8000 rpm it wasn't pretty. But I'm not an aircraft mechanic and maybe the directives are different. This brings up an interesting historical/statistical question. Has the FAA done a study of engines that had a valve break to see if said valve had ever in the past been in an engine with worn guides?

We had a 35+ year old 0-320 Lycoming with over 3500 hours. Never did anything to the block but change oil every 25 hours.

qsmx440 said:

Are the exhaust valves used in these engines sodium filled? .

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99% sure the answer is yes.

Not sure if you remember me having this issue on #4 two Falls ago Steve... but have a real GOOD look at that exhaust valve. Mine was cracked and about ready to loose 1/3 of the head into the cylinder... and all 4 were long past the wobble specs.

What kind oil oil shell 15 50 ?

I exclusively ran 15 - 50 until my mechanic convinced me about 300 hours ago that Phillips XC with Camguard was better and cheaper.

Do they make GuideGuard? That is what I need.... geeeze...

sj

There was an article I came across some time ago http://egaa.home.mindspring.com/engine1.htm discussing valve guide wear on a Mooney TLS engine. The conclusion seems plausible in that it would correct the excessive wear by increasing oil flow through the pushrod shroud tubes to the valve stems and guides, providing increased cooling and lubrication.


Wayne

That looks expensive!

cafi

Not to bad

Yes the exhaust valves are sodium filled. They have all been measured and inspected and found to be in excellent shape and will be reused. These cylinders and parts have 1200 hrs total time since new on them.

Wayne, I muddled through those articles over the weekend. The author takes you around and around and did not really come to a good conclusion. If you pump more oil to the guide it has to have a return path and a way to keep the oil from going down the guide and into the combustion chamber. Automotive engines have seals for this but aircraft engines do not. Having maintained these engines for 20 plus years I do not have the "sky is falling" outlook that he has.

We will put the new guides in and ream them to spec and dress the valves and seats before re-installing the cylinders. I will be more prudent in checking the guides and plan to document my clearances using the wobble test fixture upon re-assembly and then keep a record at every inspection there after to catch any trends. Unfortunately it will take quite a while to see if anything is happening since the airplane has 1200 hrs since 2000. I think this does make a good case for why roller rockers are an improvement but that would have to be done at overhaul since the crankcase would have to be modified. We will see what happens.

That shell 15 50 was your problem ,run 100w ,or 65w, have seen lots of engines go bad on that 15 50shell. talk to someone who does disasembles at engine shops have them tell you what they see

8GCBC said:

We had a 35+ year old 0-320 Lycoming with over 3500 hours. Never did anything to the block but change oil every 25 hours.

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Were these factory cylinders or aftermarket?

Is there a pattern here, factory cylinder vs. aftermarket or this oil used vs. that oil used?

Many industrial engines log many thousands of hours with no valve guide problems, with all the years of technology and stuff that a couple of thousand hours on an aircraft engine would be easy.

Thing that make you go huuuummm!

Valve guide wear and low compressions don't necessarily go hand in hand. As long as the valve will seal properly in the valve seat, the guides can be incredibly sloppy. Sloppy Ex valve guides will allow a lot more blowby to pump back into the crank case causing the oil to dirty up significantly quicker. I overhauled an O-470 a couple of years ago that the exhaust guides were so badly worn that the valve had nearly worn through side of the guide. It had 3/16" of clearance in the worst cylinder. Compressions were still acceptable, but the engine was starting to push quite a bit of oil overboard through the breather. As I'm sure Steve well knows, there is a real art to getting the valves, guides and seats all properly aligned and concentric. I have seen cylinders come from overhaul shops with the guides so badly misaligned that the rockers were barely over the top of the valve. This causes a lot of side load on the valves during operation causing excessive valve guide wear and premature failure.

I usually find that around 1000 hours, most engines could use new guides, but as long as the compressions are good and they aren't pushing much oil overboard, there isn't much incentive to do them.

-CubBuilder

Steve,
Double check the intake/exhaust rockers were not switched when installed. Being factory hopefully they put them in right but I've seen factory stuff screwed up before....If they are switched the exhaust valve won't gets it's squirt of cooling oil and the guide will wear fast.

That thing pulled around floats and probably did student training. Back it the good old days when I worked on a lot of working Lycs it was perfectly normal to replace exhaust guides around 1000-1200 hrs.

Also, I'd check the rings while your in there, throw a new set in and hone barrels unless the old ones look about perfect. That way it should make tbo without any more problems.

SuperCub MD said:

Steve,
Double check the intake/exhaust rockers were not switched when installed. Being factory hopefully they put them in right but I've seen factory stuff screwed up before....If they are switched the exhaust valve won't gets it's squirt of cooling oil and the guide will wear fast.

That thing pulled around floats and probably did student training. Back it the good old days when I worked on a lot of working Lycs it was perfectly normal to replace exhaust guides around 1000-1200 hrs.

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Hey Boz! Good to see ya round.

He is correct, it has been loaded heavy, rode hard, and put away wet - however, not too much "training" but lots of take offs and landing.

sj

cafi19 said:

That looks expensive!

cafi

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Maybe someone can up his weekly allowance if he cleans the windows or floors... or sumptin.

irishfield said:

Maybe someone can up his weekly allowance if he cleans the windows or floors... or sumptin.

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or make him stay home for a change.

Boz, Had squirters on both intake and exhaust. First thing I thought of too.

benflyn said:

Were these factory cylinders or aftermarket?

Is there a pattern here, factory cylinder vs. aftermarket or this oil used vs. that oil used?

Many industrial engines log many thousands of hours with no valve guide problems, with all the years of technology and stuff that a couple of thousand hours on an aircraft engine would be easy.

Thing that make you go huuuummm!

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The Lycoming 0-320 was delivered (new) in a brand new C-172L (Total cost of aircraft $17,000 from the factory). That aircraft was a money maker. Never needed anyhing special for 37 years until engine replacement. Which took 8 hours.

W100 was used.

Steve Pierce said:

.... I think this does make a good case for why roller rockers are an improvement but that would have to be done at overhaul since the crankcase would have to be modified. We will see what happens.

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Steve, Do you mean what you said? You would need to modify the case for roller lifters. I have wondered why roller rockers never seemed to catch on with the opposed engines.

If i remember right they tried them in the small continentals and the rollers wouldnt roll, just wore a flat spot. I think it was Jerry Burr that mounted a set of roller rockers to a bicycle tire on a excersie machine trying to break them in so the would roll, didnt help.

skywagon8a said:

Steve, Do you mean what you said? You would need to modify the case for roller lifters. I have wondered why roller rockers never seemed to catch on with the opposed engines.

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I'm confused, roller lifters not rockers. We need someone like Jack Roush to get interested in our small Lycoming engines. Look what he did for the Rolls Royce Merlin. http://www.enginehistory.org/Convention/2009/Presentations/MerlinNext65.pdf