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Oil type used in engines with a stuck valve

When I experienced a stuck valve, I was using...

  • Phillips Oil

    Votes: 5 29.4%
  • AeroShell Oil

    Votes: 12 70.6%

  • Total voters
    17

Earl Findlay

Active Member
A simple survey on stuck valves, and the oil type in use when they occurred. For the purpose of this survey, I am only interest in AeroShell vs Phillips, and whether each was in use at the time of a stuck valve.
 
Check out the column by Mike Busch in this months AOPA Pilot magazine. His contention is that it is more frequent when you are running cooler CHT's (like LOP operation).
 
The information in the poll will be useless unless you also know the proportion of owners using the two different oils.

Dave
 
Check out the column by Mike Busch in this months AOPA Pilot magazine. His contention is that it is more frequent when you are running cooler CHT's (like LOP operation).

That defies logic. Valves stick because of deposit build up in the valve guide. In this case, the deposits are coked oil which only occurs due to excess heat, beyond the oil's critical oxidation temp. The incidence of sticking valves should be directly related to the temperature of the oil on the valve stem and valve guide, which is not necessarily related to the oil temp at the temp sensor. The point at which oil cokes is related to it's chemical makeup and therefore can be different across brands.

I would expect a correlation between oil volume delivered to the head and stuck valves (lower flows create more heat tansfer to the oil and higher oil temps) I would ABSOLUTELY expect that running LOP would REDUCE the likelihood of stuck valves, not the opposite. Lower EGTs and CHTs, as a result of LOP op's relative tp peak EGT op's, will reduce the operating temps of the exh valve stems/guides and therefore reduce the temp of the oil clinging to them. The oil on the stems/guides is the mechanism for heat transfer from the stem to the guide and on to the head. That said, filthy rich mixtures will result in lower EGTs than typical LOP, however, who regularly operates their engine richer than peak at cruise on a regular basis. The corollary is that best power, albeit a lower EGT, will increase CHT which transfers that heat to the valve guide.

Mike is welcome to his opinions, but that doesn't obligate me to buy into them.

Larry
 
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Mike Busch's article ("Why valves stick") in the July 2020 issue of AOPA Pilot magazine posits that sticky valves are caused by lead oxybromides and not by carbonized oil. This is based on information from Ed Kollin. Mike argues that the sweet spot for CHT's, especially in Lycomings, is between 350 and 400 Degrees F to minimize valve sticking. And he explains why Continental's seem to be less prone to valve sticking than Lycoming's.

The article is definitely worth a read, whichever theory you subscribe to.

I am open to new thinking in this area, but my research indicated that combustion gas temps above 800-1000* leave the lead bromites in aerosol form and carried away with the exhaust. Lead build ups typically only occurr at idle and low RPMs, where the combustion temps are low. EGTs of 1400 should not allow lead build up on the guide any more than anywhere else in the engine where it is rarely seen.

Auto engines ran on leaded gas for decades without stucking valves utilizing similar valve/guide clearances. I remain convinced the build up is coked oil mostly due to the anemic oil flow to the rocker box on lycomings due to the use of lifters without bypass channels. The auto manufacturers figured that out in the 30's when they moved away from flat head engines. Sadly Lycoming didn't get the memo and continues to use lifters with only bleed oil. The anemic oil flow relative to auto engines creates the excess heat in the guide and therefore the coked oil buildup. The fact that lyc's don't burn oil eventhough no valve seal is used, is strong evidence to the anemic oil flow, even with the horizontal orientation. My horizontally opposed porsche engine still requires valve seals.

I would speculate that conti went with proper lifters, delivering proper oil flow, and that is the reason for the smaller incidence of stuck valves on their engines.

We have all seen lead deposits on the plug and they are dark grey. The **** scrapped out of a sticking guide is jet black and looks exactly liked coked oil (examples can be found between the two ring lands on a piston - which also appear in engines burning unleaded fuel). Further, the clearance is too tight for exh gasses to get into the guide. If that theory were correct, the lead deposits should be on the valve stem and not the guide. It would also leave the valve head fully coated.

Larry
 
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The information in the poll will be useless unless you also know the proportion of owners using the two different oils.

Dave

Not to mention the huge difference between the Aeroshell 100's and the 15-50 semi synthetic.
 
if you want to have useful info on getting a stuck valve do a wobble test. :D
P1020216.jpg
 
Marvel Mystery Oil is an excellent upper cylinder lubricant.
 
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Stuck Valve

My only experience with a stuck valve was on a Lyc. O-360, angled valve aerobatic engine. It was a 200 hp version, ?pushed? to about 230 hp by Monte Barrett. We tried Marvel Mystery Oil for a couple of hours when we suspected a stuck valve, but it still intermittently ran rough. Pulled all the valve covers and one exhaust valve would actually stick open for a second or two after pushing it open with a valve spring compressor. We did the rope trick, could see varnishy, kind of of black buildup inside the guide. Used a bit of Hoppe?s gun cleaner and a gun bore brush to remove the gunk, put it all back together and never had another problem. Everybody ran Aeroshell 100 wt. around here in those days.
 
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