The FAA issued an SAIB that all Lycoming engines equipped with certain Parallel Valve Cylinders and Head Assemblies, which were shipped from Lycoming between September 1, 2013 and April 30, 2015, have experienced cracking in service. The FAA has received reports of cylinders cracking on Lycoming engines, excluding Lycoming 0-235 series engines, between the 14th and 15th cylinder cooling fins on the intake valve side of the cylinder. Cracks may occur at any time.
These cracks may be accompanied by one or more of the following events:
– loss of power,
– rough running engine,
– high cylinder head temperature,
– cylinder head temperature spread exceeds 50 degrees F,
– whistling sound during idle or during a compression test,
– decreased cylinder and head assembly service life.
Determine if your engine contains an affected cylinder and head assembly with the local thin wall condition using Table 1 of Lycoming MSB No. 634, dated October 11, 2018, or later revision.
Next you’re going to need Service Bulletin No. 634.