Lycoming YO-233-B2A Maintenance Manual page 124

WARNING A STUCK VALVE CAN CAUSE ENGINE DAMAGE.
NOTICE: If one valve is sticking, examine all intake and exhaust valves on all of the engine
cylinders.
The exhaust valve and guide must be examined to measure valve stem movement to identify
excessive wear (bell-mouthing) of the exhaust valve guide and carbon build-up between the
valve guide and valve stem which can cause valve sticking.
Refer to the latest revision of Service Bulletin No. SB-388, Service Instruction No. SI-1485, and
Service Letter L197 for additional details.
NOTICE: The Gage (ST-71) is used to examine parallel-type valves on engine cylinders.
Although the Gage (ST-71) and a feeler gage can be used to measure valve stem
movement, a modified ST-71 (Figure 4) and a dial indicator are a faster and easier
means to measure valve stem movement, valve guide wear, and carbon build-up per
this procedure.
NOTICE: Do not intermix valve and cylinder components between cylinders. Re-install
serviceable parts in the same cylinder.
Examine the exhaust valve and guide on each cylinder as follows:
A.
(1) Disconnect power to the engine.
(2) Make sure the engine is cool.
(3) Remove one of the spark plugs from the cylinder per the "Spark Plug Removal"
procedure in Chapter 74-20.
72-30
Page 104
Figure 4
Details for Modifying Tool P/N ST-71
for Use with a Dial Indicator
YO-233-B2A Engine Maintenance Manual
TEO-540-A1A Engine Maintenance Manual
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February 2021