Service Instruction No. 1246 B

Supersedes Service Instruction No. 1246A

December 15, 2009

MODELS AFFECTED

O-235, O-290 series engines.

TIME OF COMPLIANCE

During engine overhaul or earlier at owner’s discretion.

Although solid stem valves and bronze valve guides have been an ideal combination in smaller, low compression engines, operators of aircraft powered by these engines have encountered difficulties when forced to use highly leaded fuels instead of the grades 80 and 80/87 fuels originally specified for them. The lead deposits that are associated with the use of high lead content fuels cause valve erosion and accelerated valve guide wear. These conditions can be alleviated by replacement of the solid stem valves and bronze guides with sodium cooled valves and guides made of ni-resist alloy. At the time of new exhaust valve replacement, also install improved intake valves P/N 17A23939.