I’ve become aware of quite a few engine cylinders across different aircraft that needed repair or even replacement in the past year or two. The ones I know of are all Lycoming. Sometimes these are from aircraft that have flown only a few hundred hours since last overhaul, and I wouldn’t have expected that. This fault can be where the exhaust valves and/or guides are damaged. Recently our engineering shop sent a batch of five from different aircraft to be repaired. Is this becoming a more common problem and if so, what’s the underlying cause?
Often I’ve been told the cause is aggressive leaning at low level. Other causes could include
- rapid acceleration with carb heat on
- over priming prior startup
- poor or mistimed magneto spark especially during startup (could be fixed by electronic ignition)
- turning off the mags when running (eg when doing a mag check)
- changes in fuel composition
- lower quality manufacture of components
Has anyone else noticed this as a trend and/or found the likely cause and operating procedures to mitigate?
DavidC wrote:
Often I’ve been told the cause is aggressive leaning at low level
Why would the level matter? Except of course that the higher you go the lower the maximum power and the lower the power the less likely you are to damage anything. (At least with a normally aspirated engine.)
Can you define “cylinder damage”?
DavidC wrote:
Often I’ve been told the cause is aggressive leaning at low level.
That is pretty much many mechanics’ answer to most valve- or cylinder-related problems. I (choose to) think valve guide issues are more likely to be caused by overly rich mixture and use of Aeroshell 15W50.
You should read Mike Busch’s new book ‘Engines’, he covers these problems quite extensively. I am only at page 100 or so (of 500) but can highly recommend it for anyone owning or operating a piston engine.
Aviathor wrote:
I (choose to) think valve guide issues are more likely to be caused by overly rich mixture and use of Aeroshell 15W50.
what is the reason behind this? in particular aeroshell 15W50
You can and should lean from 0 feet upwards, in cruise configuration. Lean while taxiing, full rich for take-off and climb, your cylinders and sparkplugs will thank you.
Peter_Paul wrote:
what is the reason behind this? in particular aeroshell 15W50
You can get some feel for it here and here if I am not mistaken.
@achimha made some interesting remarks that corroborate Mike Busch’s claim about synthetic oils not keep particulates in suspension. It may be in one of the threads quoted above. The particulates then form sludge that can coke between the stem and guide. There is one article where he is particularly vocal about his feelings towards Aeroshell 10W50, and explicitly recommends not using it.
Aviathor wrote:
Often I’ve been told the cause is aggressive leaning at low level.
That is pretty much many mechanics’ answer to most valve- or cylinder-related problems
+1
We had our engine redone in 2014 and since then had 3 cylinders replaced, in different repair shops.
They all tell me cylinder quality has gone south over the last 2 decades. Sounds like a problem to me.
I wonder if this correlates with having a turbo? Turbo engines are usually right on the margin.
