Just borescoped them all – doing this now at every service
It’s funny how they can all look so different, but there can be some of this going on. Before this service I did a taxi/warmup with the engine heavily leaned – as one always should when on the ground.
Does anyone else here borescope their engine regularly?
your valves look good Peter 
I get to borescope a few engines a year myself, and as the Maintenance Manager within our EAS (Experimental Association of Switzerland), helped set-up our OCM (On Condition Monitoring) program. This embraces most of the HB-Y.. homebuilt aircraft. Whilst the person performing maintenance on said aircraft has to perform additional tasks, such as borescoping every 100h/annually, in return they can then fly past calendar and hour TBOs. Some builders take years to finish their project, or fly very little, then easily hit e.g. the 12 years overhaul recommendation.
Our borescope inspection requires looking at each valve, piston crown, cylinder wall, and cylinder head for cracks between the spark plug holes or between the valves. On exhaust valves a circular pattern with no discolouration (greenish) is all good, pizza look is good.
One of the best assessment tool, courtesy of AOPA, here: AOPA Borescope Chart local copy
Note, on most Lycos only the exhaust valve is rotating…
Peter wrote:
Does anyone else here borescope their engine regularly?
When the engine is running beyond the manufacturer’s recommended TBO, yes, every 100 hr.
Yes, each time the spark plugs come out I stick the borescope in.
terbang wrote:
Yes, each time the spark plugs come out I stick the borescope in.
Same here, minimum once a year (annual, N-reg).
Same here, decided to replace two cylinders now almost a year ago based on a scheduled borescope, exhaust valves showed they were burned, green to the side with no concentric pattern…I could have changed the rotocoils but decided it was best to replace cylinders not knowing the life expectancy of the valves…Some swear by religion to replace all rotocoils after 600 Hrs……
Vref wrote:
…I could have changed the rotocoils but decided it was best to replace cylinders not knowing the life expectancy of the valves…
Seems that there are a lot of cylinders being replaced when we can just lap the valves, and replace the rotocoils.
we can just lap the valves
Are you an engine shop, @eurogaguest1980? If so, you may be able to offer a view on why this is.
My view is that Europe is very short of competent engine shops, so a lot of stuff gets chucked away. However, at some GBP 1k per cylinder, a lot of people who do a “top overhaul” regularly (most turbo Lyco/Conti engine owners) tend to take the view that replacing whole cylinders is easier.
your valves look good Peter
Thanks I still think it is bizzare how the valves vary. I could produce six different pics every time I do this. It’s same with spark plugs, but with those I am very certain their condition is mostly based on the last few minutes, so useless for indicating what the engine is doing in cruise (unless, of course, the spark plug has mostly disappeared, in which case you are probably running, ahem, just a little hot 
).
Peter wrote:
Are you an engine shop, @eurogaguest1980? If so, you may be able to offer a view on why this is.
No, but I listened to a podcast, so now I’m an expert!
https://airplaneownermaintenance.com/109-exhaust-valve-problems-could-lapping-be-a-good-option/
https://resources.savvyaviation.com/wp-content/uploads/savvy_pdf/exhaust-valve-lapping-paul-new.pdf
https://www.avweb.com/ownership/the-savvy-aviator-56-before-you-yank-that-jug/
Basically, it seems that most A&Ps are taught “low compression, change the cylinder.” They are not (yet) taught borescoping, or valve lapping, or the impact of a broken rotocoil. Also, it seems that compression tests are not a really good indicator of cylinder health. Good numbers like 78/80 are of course good, but even 40/80 could be ok the next time you test. If you have low compression, go fly for an hour and test again – you’ll get different numbers.
Well, yes, that pretty well describes the aircraft maintenance scene generally
Nobody has a monopoly on illiteracy so a lot of stuff gets done by following “the simple route” which may financially disadvantage the client but minimises the risk of a comeback on the engine shop, whereas “cylinder work” would expose the shop to client unhappiness if they do a bad repair.
