Maintenance question for engine over TBO
Can anyone point us in the right direction?
I am part of a syndicate which runs a C172P on a UK private C of A. The engine (O-360) is over Lycoming's recommended TBO (now with about 2,300 hours on it) and we are operating it "on-condition". We have run this aircraft for over 20 years and it is very well maintained and used very regularly. We regularly run engines to over 2,500 before overhaul (we are on engine number 3 so far), as long as the certified engineer (and we pilots!) are happy that it is safe and legal to do so.
Here is the question: we have identified low compression on one cylinder (still within limits), and the engineer says it is a very simple fix as the valve probably needs re-seating. However, he also says that as it is "on-condition", he is not allowed to remove the cylinder head, but that the whole engine must be overhauled. If that is true, fair enough, but I like to see these things in writing. I've looked through LAMS/CAP411 and cannot see the reference. I don't have the C172 log-books to hand to see if it is referred to in the specific maintenance schedule for the type. Can anyone point me to where it says no part-disassembly of the engine once over recommended TBO?
Thanks in advance!
Nothing to stop you pulling a cylinder and having a look, may be valves need lapping in or replacing, in which case get a top end overhaul done on the cylinder, you might even find it is rings lining up, did you run it after you had the low figure and recheck it again? you could do the rings too if the cylinder is within limits.... take it your man checks the filters every 50 hour for metal etc..... to be honest it could just simply be a bit of carbon on the valve seat which you could possibly do without taking anything off.
GRN 24 covers it and you can pull cylinders...