I found this while looking for something else. It is an interesting article, but long.
http://www.prime-mover.org/Engines/Marvel/tbo3.html
Jim
http://www.prime-mover.org/Engines/Marvel/tbo3.html
Jim
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Lycoming valve train lubrication issues
- Thread starter jim
- Start date
marshmaster pat
Well-known member
Jim - I believe there was a fairly large online discussion on a similar article about 2 or 3 years ago. There is a great Lycoming Yahoo site for pilots, owners, and homebuilders that is ran by a builder with a very great reputation.
The Lycoming Yahoo group had a several weeks of discussion on it as well. While several of the builders that contribute to the discussion agreed, there were a couple from very well known aircraft shops that said while the oil delivery system is not a good as it could be, it is sufficient enough to do the function that is needed. Almost all pointed that there is a potential issue, the issue is not a problem if CHTs are closely monitored and ran on the low to mid range of recommendations. They all pointed out that many people are trying to run as lean as possible, with CHTs getting near the upper maximums to conserve fuel. Running an engine that costs between $25,000 to $50,000 new and they are trying to save $100s a year in fuel was foolish in their opinion.
This was especially true since most claimed that the range of CHTs could be as wide as 40 to 60 degrees. And since quite a few aircraft monitor only 1 cylinder, if it was a cooler one and you are running lean with CHTs set at near maximum, you could easily smoke a cylinder or cause valve issues.
One builder claimed there might be another issue. He claimed that the mold process that Lycoming uses on the cylinders, tends to allow some of the fins below the spark plug to have slag blocking the cooling channels. It was his thought that this, combined with low oil movement, would increase temperature enough directly around the valves to cause issues. He claimed that it was not uncommon for them to get new cylinders in with these ports plugged with slag/flash. They would grind them open and had no issues with motors since starting this.
However, there are some adaptors that are being sold to help increase oil movement this area of concern.
Good Article, Thanks
The Lycoming Yahoo group had a several weeks of discussion on it as well. While several of the builders that contribute to the discussion agreed, there were a couple from very well known aircraft shops that said while the oil delivery system is not a good as it could be, it is sufficient enough to do the function that is needed. Almost all pointed that there is a potential issue, the issue is not a problem if CHTs are closely monitored and ran on the low to mid range of recommendations. They all pointed out that many people are trying to run as lean as possible, with CHTs getting near the upper maximums to conserve fuel. Running an engine that costs between $25,000 to $50,000 new and they are trying to save $100s a year in fuel was foolish in their opinion.
This was especially true since most claimed that the range of CHTs could be as wide as 40 to 60 degrees. And since quite a few aircraft monitor only 1 cylinder, if it was a cooler one and you are running lean with CHTs set at near maximum, you could easily smoke a cylinder or cause valve issues.
One builder claimed there might be another issue. He claimed that the mold process that Lycoming uses on the cylinders, tends to allow some of the fins below the spark plug to have slag blocking the cooling channels. It was his thought that this, combined with low oil movement, would increase temperature enough directly around the valves to cause issues. He claimed that it was not uncommon for them to get new cylinders in with these ports plugged with slag/flash. They would grind them open and had no issues with motors since starting this.
However, there are some adaptors that are being sold to help increase oil movement this area of concern.
Good Article, Thanks
Pat,
It's nice to have you back. I hope everything is approaching normal. I always enjoy your posts. I would be interested in hearing about the mods. These type of mods are very difficult to do in a certified airplane and that may color some of the rebuilders remarks.
I know that my son's engines have modified oiling systems, but the builder is sort of tight lipped about that. They are getting more HP than anyone else and they want to keep their edge I guess. He runs it quite rich.
These aircooled engines can be oil cooled by spraying oil on the bottom of the pistons and on the exhaust valves I think. I suspect they spray the cam also. It looks like to me that you could just tap into a pressure gallery and spray it directly on the exhaust valve with external lines, if the pump has enough capacity. My son's engine does not have any extra external lines that I recall.
I have not visited the Yahoo Lycoming site in a while.
Take care,
Jim
It's nice to have you back. I hope everything is approaching normal. I always enjoy your posts. I would be interested in hearing about the mods. These type of mods are very difficult to do in a certified airplane and that may color some of the rebuilders remarks.
I know that my son's engines have modified oiling systems, but the builder is sort of tight lipped about that. They are getting more HP than anyone else and they want to keep their edge I guess. He runs it quite rich.
These aircooled engines can be oil cooled by spraying oil on the bottom of the pistons and on the exhaust valves I think. I suspect they spray the cam also. It looks like to me that you could just tap into a pressure gallery and spray it directly on the exhaust valve with external lines, if the pump has enough capacity. My son's engine does not have any extra external lines that I recall.
I have not visited the Yahoo Lycoming site in a while.
Take care,
Jim
A
Anonymous
Guest
Hey Pat,
One obvious advantage that the Continentals have over the Lycomings is that the cam is below the C/L of the cylinders, instead of above them. The Lycomings have to rely on 'splash' lubrication for the cam and valve train. They'll live a long time with the RPM's up, as in 'in flight', but they cook when they're asked to do a lot of idleing because the cam bearings and pushrods are running dry by comparison.
The Continentals have the cam and pushrods below the cylinders, so those pieces are in oil most of the time. Big difference.
Jim's son's engines may have been modified to provide pressure lubrication to the cam. That would make a huge difference in reliability.
Ken
One obvious advantage that the Continentals have over the Lycomings is that the cam is below the C/L of the cylinders, instead of above them. The Lycomings have to rely on 'splash' lubrication for the cam and valve train. They'll live a long time with the RPM's up, as in 'in flight', but they cook when they're asked to do a lot of idleing because the cam bearings and pushrods are running dry by comparison.
The Continentals have the cam and pushrods below the cylinders, so those pieces are in oil most of the time. Big difference.
Jim's son's engines may have been modified to provide pressure lubrication to the cam. That would make a huge difference in reliability.
Ken
A
Anonymous
Guest
It's my understanding that there is an oil additive specifically engineered for Lycoming engines to help keep the lifters from galling.
I am not sure if all aviation oil has this additive, but the article seemed to indicate that it is only found in certain oils.
I am not sure if all aviation oil has this additive, but the article seemed to indicate that it is only found in certain oils.
A
Anonymous
Guest
Pat, I just thought of something that is real important for your Lycoming:
There's a Lycoming maintenance bulletin that I remember reading a couple of years ago that says something to the effect that after you change the oil in that beautiful 540
(I love 'em), pull the spark plugs and crank the engine through on the starter until you get oil pressure. Then replace the plugs, and you're good to go until the next oil change.
This will take the load off of the rod bearings (and starter) while you're purging the oil system of the air that accumulated when you drained it, and prevents a 'dry start'.
Ken
There's a Lycoming maintenance bulletin that I remember reading a couple of years ago that says something to the effect that after you change the oil in that beautiful 540
(I love 'em), pull the spark plugs and crank the engine through on the starter until you get oil pressure. Then replace the plugs, and you're good to go until the next oil change.
This will take the load off of the rod bearings (and starter) while you're purging the oil system of the air that accumulated when you drained it, and prevents a 'dry start'.
Ken
marshmaster pat
Well-known member
Ken - That makes sense to me, and is not that big of a hassle. It would well be worth the effort if it prolongs the life of the engine, especially at the cost of them. Something to remember next time I change the oil.