However I think the post year 2000 IO540 population may be very small. Most engines actually flying in private use are much older.
But wouldn’t a significant number have been overhauled since 2000, and if so be fitted with “C” ?
But wouldn’t a significant number have been overhauled since 2000, and if so be fitted with “C” ?
Good point, but how many private owners (not many IO540s or even 360s are in the training environment) reach 2k+ hours in say 14 years?
I wouldn’t pull and rework perfectly good cylinders to replace guides, unless they were worn out. Beyond that a fair proportion of cylinders operating on existing Lycoming engines are PMA cylinders that weren’t manufactured by Lycoming.
Re the valve guide tests, its amusing the number of ‘mandatory’ service bulletins manufacturers are starting to put out, and I think the issue for them is to guard against crying wolf and being ignored. Obviously for most Lycoming engine owners they aren’t actually a mandate, and their real purpose before the lawyers got entrenched was to give the A&P some guidance.
I was puzzled by the seemingly unrelated coincidence of the blown exhaust gasket being the cylinder with the stuck valve. I discussed this with the group the first night, and a retired Continental Engines engineer explained it to me: If the exhaust gasses are not carried well away from the cylinder as intended, that cylinder will get locally hotter than intended.
That sounds like a nice way of saying when the exhaust comes loose, the air leak into the exhaust lights off any unburned hydrocarbons and makes gunk in the exhaust port.
I check exhaust system security before every flight, possible because my planes have cowlings that allow good access. I’ve yet to find a loose exhaust nut but I’ll keep a close look out now. I’d hate to have an engine problem as a result of something so simple.
Can someone explain the rope trick please? I understand it’s a clever way of avoiding having to remove the cylinder in order to re-install the valve, but how?
Stickandrudderman, it’s about stuffing the cylinder with rope through the spark plug hole to prop the valves closed.
Yup, rope in the spark plug hole. But, from recent experience, 3/8" rope is too small, for the 360. At one point, I had the rope pinched under the open valve, and pulling it was jut making it more tight. I had fears of having to remove the cylinder, just to get the rope out. Some cunning manipulation through the other spark plug hole got the other end out, so I could work one against the other, and that got it out. As I ended up removing the exhaust, that would have been my other opportunity to free it. Bear in mind that the rope trick is still of little use if you do not have the proper tools and ability to remove the valve keepers, and get the valve out.
And “C” cylinders did not solve the valve sticking / wear issue, they only improved it a bit
Googling suggests that it improves it to the point where it doesn’t matter at all. I have certainly never heard of anybody else with a TB20GT (year 2000 on) with the issue.
I have posted the question in a maintenance forum and within a few hours, I had three responses of people with a Lyco 540 and “C” cylinders that experienced sticking valves. One 200h after overhaul, another 700h and the third one 750h.
So the “C” cylinders really do not make a big difference for the sticking valve problem but they improve on the valve guide wear and the cooling. Some good background and plausible explanations on the sticking valve and valve guide wear issues can be found here.
I wonder if there is a correlation between this issue, and CHT?
The reason I think this is that a sticking valve is a hugely inconvenient AOG item, and if it was that common on TB20s I would have heard more about it.
Sorry to bang on about it but:
When I want to hold a valve in place whilst removing the spring I use compressed air through the plug hole. Now I can see how a piece of rope might perform the same task but how does it allow you to remove the valve so you can ream/clean the guide and then re-install that valve?
