Exhaust Valves Stuck Open
After carrying out mandatory Service Bulletin SB11-73-01, it was found that the exhaust valves in position 3 and 4 were stuck partially open.
Transport Canada Comments:
Transport Canada Civil Aviation recommends that maintainers be familiar with manufacturers additional support publications. In this case, Lycoming Service Instruction 1425A and of course mandatory Service Bulletin 388C are applicable.
The following is an excerpt from Lycoming Service Instruction 1425A:
“Field experience has shown that engine oil contamination increases the possibility of sticking and/or stuck valves. This situation occurs when the contaminants in the engine lubrication oil become deposited on the valve stems, restricting the valve movement, and resulting in intermittent engine hesitation or miss. If corrective action is not taken to remove the deposits, a valve could become stuck causing engine damage.”
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