In our typical aero engines, the smaller one is the exhaust valve.
Pardon the dumb questions, but is the small/coloured valve the exhaust valve? Is the size difference consistent across engine types/manufacturers? I.e. when boroscoping, how does one know which valve is input and which is exhaust?
I understand that one can tell whether a leak is rings or valve by listening during propellor rotation. However, knowing that it is a valve, looking at the photos above, it isn’t obvious to me which valve is the one that’s leaking. Suggestions?
Great news on the camshaft etc. Sounds like, as long as you keep flying regularly, with the odd cylinder, the engine has years of safe flying left in it.
Thanks for posting all of the photos and the ending – a good educational thread for me.
AFAIK if you change any of
then the cylinder needs to be re-honed and a new piston and rings fitted. This is because the new combination won’t “bed-in” unless you have a fresh hone (the criss-cross pattern).
In fairly rare cases they pull off a cylinder and put it straight back on, with nothing touched, and that is ok.
You now need to follow the Lyco bedding-in procedure (including the correct oil and without camguard). The first few hours of it are particularly critical.
Excellent news on the bottom end. It’s great to have that data point. It can be done without pulling cylinders but very few people know that.
Re the future, always fly at peak EGT, going to “best power” (c. 150F ROP; typical EGT there is about 1350F) only during climb.
So, to answer Peter’s question, in an earlier message on this thread I explained that the exhaust valve is the source of the pressure leak. It’s leaking a lot. Can it be lapped? I’m told not because it’s too far gone and anyway the cylinder has lost its cross-hatching… I’m an accountant (albeit with a science background) not an engineer.
The good news is that the people looking after my plane have told me how pleasantly surprised they are by the condition of the bottom end of the engine. The cams are in excellent condition, so a big money engine repair seems unlikely for a good few years. I do now and have for two years used Camguard. I have no idea if that is correlated with the good condition of the cams.
New cylinder is on its way…I’d love to know more about whether that was the only possible good decision, but the people looking after my plane think so, and it’s certainly a safe decision.
H
Morning @Howard
When you said “he did something with oil”, perhaps he poured some oil through the top spark plug and when he performed the air test for the second time, this provided a temporary seal?
If I were you, if it’s not too late I’d hang onto that cylinder (even for future use) as I am guessing the real issue might be a gummed up piston ring, This will be “cured” when the cylinder comes off. Putting the old cylinder back on (perhaps with a couple of new valves) would save having to run in the new cylinder.
Is there a way to cancel the new cylinder? As I said, I might well be completely wrong, I am not that experienced and I’m only looking at photos, but that’s my hunch.
By the way, on the bright side, you mentioned you have an old engine. This is a fantastic opportunity to inspect the camshaft and followers. What is it like? There is no reason that your engine can’t go on for years if the cam is in good condition.
That’s why I asked “Can anyone see anything obviously wrong with that cylinder?”.
Not sure if any good engine builders read EuroGA. I used to know a good one but sadly he became ill…
I regularly borescope my engine so this is an excellent case study where I can learn more
So is the issue a piston ring not the cylinder? – Also as we know low compression does not affect power, was it too early to pull this cylinder off?
I’m no expert so any feedback to explain where I have gone wrong on my analysis welcome.
problem moved from exhaust valve to glazed cylinder.. One other Q is it common to mix sparkplug types?
Which of the valves has been found to be leaking?
Can anyone see anything obviously wrong with that cylinder?
