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O-320 exhaust valve guide wear

irishfield

irishfield

Registered User
Penetanguishene, Ontario Canada
What are you guys doing to prevent this? My #4 cylinder, for the last 2 Springs, has needed a couple hits to stake and get 72/80. I thought it was from sitting through the winter with that exhaust valve possibly open and surface rusting and didn't think it was a big deal. This year the day I came home from camp I thought I'd do a compression test to prove that to myself, only to find to my dismay 58/80 and roaring out the exhaust.

I was going to try the rope trick and a valve lap.. but once I got the springs off I found the valve to guide clearance was like throwing a wiener down a hallway.

I just finished pulling all 4 cylinders to drop off at the local engine shop for valve guide replacement, as I was told if one was done they all would be. Curious what others are finding and if there is anything that can be done to prevent it. My engine only has 215 hours SMOH and I only run 100LL.. no car gas.

The only good news today... my cam lobes are mint and my lifters don't have any pitting! :D

Thanks!
 
Check your springs. If they are shiney, polished on the bottom where they sit on the head then they are rotating...which means the valve is bouncing as it closes. Weak springs make the valves wear faster.

My recent experience.

25% of the guides in my cylinders could be pushed out with your thumb. The cylinder guru here fits each guide before installation.

Tim
 
Thanks Tim... didn't notice any shine on the springs when I had #4 apart.. but will have a good look when they come apart at the engine shop on Monday. I have a full set of in/ex valves and many O-320 springs for spares if need be.
 
Could you eleborate further. It's always been my knowledge that valves have to rotate or they will carbon up and either burn or coke up and not close. Some engines actually have a ratchet type mechanism on the valve to turn it slightly with each revolution. Anyway is an aircraft engine somehow different in this respect? Or are you saying that with weak springs they rotate to much (more than normal)?


behindpropellers said:
Check your springs. If they are shiney, polished on the bottom where they sit on the head then they are rotating...which means the valve is bouncing as it closes. Weak springs make the valves wear faster.

My recent experience.

25% of the guides in my cylinders could be pushed out with your thumb. The cylinder guru here fits each guide before installation.

Tim
Click to expand...
 
Tim is talking about the valve spring rotating. The valve should rotate and the exhaust valve has a rotator on top of it between the rocker arm and the valve.

I have had two cases recently of the opposite problem. The valve guides were too tight on an O-320 I built with new Superior cylinders and an O-360 that had new cylinders from Lycoming I believe. Reamed the guides and fit the valves and all was good.
 
Tim C:

Not to hijack the thread, but Can you elaborate publicly what went wrong with your cyls? Flying Miss Daisy kind of filled me in at the WAD, it sure makes your face turn red to hear those kind of stories. Just trying to learn, send me a PM if you like, thanks

Jim
 
Running "nothing but 100LL" is probably what causes premature guide wear...your engine was designed to operate on 80/87. 100LL has four times as much lead as 80/87! If you mixed your 100LL with unleaded mo gas at least 50/50, you wouldn't have all that exess lead adhering to your metal parts....
 
I've had the wiener down the hallway problem also at 250hrs. But mine was because someone installed the rocker arms (intake and exhaust) backwards. The exhaust rocker has a oil hole to oil the valve stem, therefore it was oiling the intake stem.
David
 
My Dad runs about 90% mogas and that is why we were real surprised that he had a tight guide. Have found several engines with the exhaust and intake rockers reversed like Dave mentioned.
 
I'll have a good look at them.. but considering the oil all over each exhaust stem "button" I don't think it's an issue and I slid both rockers back on the rocker shaft as I disassembled... so they are properly oriented for reassembly.
 
Well kick me in the nads... all 4 cylinders... rocker with the weeper hole for extra oil.... is on the intakes.

EDIT... they are actually correct. I was thinking the extra bleed hole on the one rocker was the oiler.. it is not and it's supposed to be on the intake side. The exhaust side has a small hole under the valve side of the rocker arm that sprays oil at the valve.
 
Well it sucks, but at least its closure to the problem. In my case no one is owning up to the problem. Learn and move on.
 
Those of us that run small Continetals have a guide problem sometimes, check the angle that the overhauled rocker has, if the angles not close to the same as the valve stem it pushes the valve away from the rocker with every downstroke and prematurly wears out the guide and the lead in 100 LL will fill in the void and make it stick, if you run 100LL on a low commpression engine you need to ream new cylinders guides 1 or 2 thousands larger. OPINION your milage may vary, but in 2700hrs I've never had a stuck valve.

Glenn
 
Dropped my cylinders for new guides today. Brought a couple rockers with me to clarify their positioning and they were indeed correct on the engine originally. The intake side rocker has the large bleeder port on the top face of the rocker to let the oil flow thru and into the rocker cover. The exhaust side has a small spray hole under the valve side of the rocker arm to spray oil.

So it's just wear from poor rocker angle design and the dreaded 100LL. I was told running car gas just pounds the valves right into the seats though... so I think I'll stick to the 100LL or a bit of a mix.
 
irishfield said:
I was told running car gas just pounds the valves right into the seats though... so I think I'll stick to the 100LL or a bit of a mix.
Click to expand...

The inventor of Camguard believes that mixing the two, 100LL and Mogas, is worse for the engine than running a steady diet of either. In broad general terms and paraphrasing. The combustion byproducts of Mogas deposit more precursors in the engine than using 100LL. However, when the two are mixed, the excess lead from 100LL mixes with these precursors and thickens them, "like pigment in paint". Clogging valve guide and causing sticking, premature wear, among other things

Running only 100LL, the excess lead doesn't have these precursors to adhere to and "thicken" so, as the theory goes, they won't stick to engine parts as readily.

Running mostly Mogas, some "operators" retard the timing a degree or two, to offset the effects of it's decreased latency (the flame front gathers itself and gets going more quickly than 100LL and changes the "effective timing" or what the egine feels), delaying the pressure pulse and softening the combustion event.

I have run Mogas almost exlcusively for nearly 3000 hours now, with no problems. The "pounding" of the valve seats from using Mogas seems to be an OWT form everything I can find. It was an assumed crossover problem from the Automotive world when they tried using heads without hardened valve seats. Which was never a problem with Airplane engines because they have always had hardened valve seats, from the beginning.
 
Valves

I don't know who the inventor of Camguard is? So who cares? I do know from experience that lead builds up in low compression/lower operating temperature cylinders. Removing the amount of lead from the fuel burned, results in less lead having to be scavenged out through the exhaust gas. The higher compression/temperature operating cylinders scavenge the lead, as the lead is vaporized in the hotter exhaust gases....Temperature is the determining factor in how well your exhaust gases scavenge lead....
 
Re: Valves

nanook said:
I don't know who the inventor of Camguard is? So who cares? I do know from experience that lead builds up in low compression/lower operating temperature cylinders. Removing the amount of lead from the fuel burned, results in less lead having to be scavenged out through the exhaust gas. The higher compression/temperature operating cylinders scavenge the lead, as the lead is vaporized in the hotter exhaust gases....Temperature is the determining factor in how well your exhaust gases scavenge lead....
Click to expand...


Ed Kollin is the inventor of Camguard, among other things. He was a Chemist at Exxon and developed Exxon "Elite" Aviation Oil for them. In short, he is an expert on the subject.

Low compression and High operating temperatures are NOT mutually exclusive, the mixture controls the operating temperature, not the compression ratio.

Here is his reply to a similar question on another forum:

"Deposits are from raw and partially combusted fuel (deposit precursors) from blow-by. A deposit starts as a thin clear lacquer, becomes thicker and oxidizes further to a varnish, oxidizes further to soft black carbon (O-300s and NA Lycomings fall here - sticky valves) and oxidizes further to hard carbon (Large bore continentals fall here - worn valve guides). Lead bromide particles floating around the oil are very soft and are 1 micron in size (25microns = approx. 0.001 inches). They are captured in the deposits and build up their thickness (fill). They are like the pigment in paint.

Suspension of the lead by the dispersant is not possible they are too big. Dispersant's bond to deposit precursors.

Lead scavenging (ethylene dibromide) keeps the combustion chambers, plugs and exhaust valves clean. It does nothing (good) for the oil.

Auto fuel is less stable than avgas and puts a higher percentage of precursors into the oil but if you only use auto fuel there are no lead particles to "fill" and thicken the deposits.

Aggressive leaning is the only way to keep the fuel out of the crankcase.

Increased CHT will increase deposit formation while decreased CHT will decrease deposits but the deposits may be "stickier".

My opinion is that alternating auto fuel and avgas gives the most deposits.

What is the ignition timing on an O-300?

Regards,

Ed "
 
Sticky valves

Ed, I'm impressed that your are quoting an Exxon engineer named Ed. I hope they screen their engineers better than they do their oil tanker captains...Question: If there is too much lead present in the combustion chamber, where does it end up? Answer: All over the place...After 30 years of building, tearing down and flying aircraft engines of all sorts, that's my conclusion....I burn a 25:75 ratio of 100LL to Mo-unleaded when I have to run a higher octane mix. If you don't need the higher octane, run straight Mo-unleaded.....Run too much lead in your combustion chamber and it will be all over everything.....
 
Re: Sticky valves

nanook said:
...... 30 years of building, tearing down and flying aircraft engines of all sorts, that's my conclusion.....
Click to expand...

I think you said it best in your previous post, "So who cares?"
 
sticky valves

Yeah, who cares that the inventor of something or other says it is ok to run straight 100LL...After they pulled 80/87 off the market, (those of us who are old enough) remember running 100LL for the first few hundred hours and having to pull the bottom plugs at 25hrs. and chiseling the lead out....But gee it must be okay now, because some engineer at exxon says the lead won't adhere to anything.....Give me a break.....
 
Re: sticky valves

nanook said:
Yeah, who cares that the inventor of something or other says it is ok to run straight 100LL...After they pulled 80/87 off the market, (those of us who are old enough) remember running 100LL for the first few hundred hours and having to pull the bottom plugs at 25hrs. and chiseling the lead out....But gee it must be okay now, because some engineer at exxon says the lead won't adhere to anything.....Give me a break.....
Click to expand...

You have misquoted what he said and in the process, missed the point entirely. It is NOT that "lead won't adhere to anything" when running straight 100LL, it is that alternating between the two, MAKES IT WORSE. There is a clear difference with a distinction between the two statements.

You could benefit a great deal by taking the time to revisit the subject.
 
auto fuel and valves

over 2200 hrs on my lyc 0320. almost all of it on auto fuel, 100 ll gets put in when I cant get auto gas. I have heard it all about how auto fuel does this and that. When you get down to brass tacks these old engines do better on auto gas than 100 ll. I save a lot on fuel , but the real savings are on my valves , plugs and cyl wear.
 
Let me ask the dumb question---so if lead from your fuel is causing problems for the valves, how does it manifest itself? Stuck valves? Or that wobble in the valve guide?

I know there is that Service Bulletin (I think...) that talks about how to check for valve guide wear. I was also under the impression that after a certain manufacturing date the valve guides were changed somehow to end or curtail the problem. No?

Or are these two different issues?

I just run AvGas and lean the bejesus out of my engine on the ground and even at low altitudes (unless at high power settings). At 500 hours no obvious problems...yet...

Thx for the education.
 
3 of 4 of my cylinders are 76/80 to 78/80. #4 has been an issue for 3 years now.. needing staking after winter lay up to get 72/80. Fresh in from summer it was 58/80 and guide worn out. I was told if one was like a wiener thrown down a hall way they would all be the same... and disassembled today THEY ARE!

Others in another forum suggested NI- steel guides were the answer. I was told by the engine shop absolutely not.. there are bigger problems going that way than having the alum/bronze guides wearing out.
 
Valve guides and seats seem to be an issue with the 0-320. I've had to replace two cylinders since my eng was OH and in both cases it was because of valve guides and loose seats.
 
Rob, IrishField,

Out of curiosity, what kind of cylinders are we talking about? Factory new Lycoming, "field" overhauled Lycoming, Superior, ECI??????

Thanks
 
Both were OH cylinders done by an engine shop, but don't think they did the valve seats in house. Will try to find out.
 
yes.. Ni-resist is what I meant to type. I was told not to go that route by the engine builder I dropped them off at. He's been building engines for over 40 years. (whether that's good or bad, or he's set in his ways?? lol)

The actually cylinders on my engine are Chrome.. and were "first run" before my engine was overhauled for me by Leavens Aviation. Cylinders are still STD size and when dropping them off on Monday my builder noted by the way the valves sit high in the seats... they where probably new with all that "meat" left and will clean up easily.
 
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