Running a mechanic’s magnetic pickup tool around in the drained oil is a good idea for any
engine, but particularly for Continental engines where the suction screen cannot be inspected.
How to ensure nothing is coming apart inside your crankcase
BY MIKE BUSCH
I’D BEEN WORKING WITH a Bonanza owner in Memphis for several
weeks helping him chase down a problem with his Lycoming engine.
Yes, Lycoming—the aircraft was an A36 with a Machen conversion to
a fire-breathing 350-hp Lycoming TIO-540-J2BD engine. The
owner of this hot-rod Bonanza initially reported that the engine had
exhibited several episodes of rough running after start-up, but that
the engine seemed to run smoothly once it warmed up.
The No. 1 cylinder oil spray nozzle and its
Heli-Coil had come out, bounced around
inside the engine, managed to hit all six
pistons, and scored two connecting rod
The owner e-mailed me a data dump from his JPI engine
monitor, which confirmed my suspicions that his “morning
sickness” was caused by a couple of sticky exhaust valves in
cylinders No. 4 and No. 5. Sticking exhaust valves is a fairly common
malady in Lycomings, which is why Lycoming Service Bulletin 388C
and Service Instruction 1481A call for doing a “valve wobble test”
every 400 or 1,000 hours (depending on what kind of exhaust valve
guides are installed).
The owner wound up taking his sick
engine to an excellent engine shop near
Memphis. The shop pulled the rocker covers
and found the No. 4 exhaust valve springs
black with carbon from a badly leaking
exhaust valve guide. No. 5 had the same
problem, but not quite as bad.
But this article isn’t about sticky valves.
It’s about something much more serious.
The engine shop decided to inspect the cam
and make sure it was not damaged by the
valve-sticking episodes. In most Lycomings
(unlike most Continentals), you can’t remove
the lifters from the outside of the engine, so
the only way to inspect the cam is to pull a
jug. The shop proceeded to pull cylinder No.
4, and it turned out to be a lucky thing it did.
The owner e-mailed me:
“They pulled the No. 4 cylinder and
found evidence of damage from a screw
hammering the bottom of the piston. They
also found marks on the crankcase on one
side of the cylinder base. The engine was
removed and torn down. They found that