Piston Ring Replacement - Lycoming TEO-540-C1A Maintenance Manual

11. Piston Ring Replacement

CAUTION DO NOT UNDER ANY CIRCUMSTANCES INSTALL CHROME-PLATED
PISTON RINGS IN AN ENGINE HAVING CHROME-PLATED CYLINDER
BARRELS. IF YOU ARE UNSURE OF THE CORRECT COMBINATION OF
PISTON RINGS TO BE USED, REFER TO THE TEO-540-C1A ILLUSTRATED
PARTS CATALOG.
DURING REMOVAL OF THE THREE PISTON RINGS IN THE NEXT STEP,
USE CARE NOT TO SCRATCH OR SCORE THE PISTON. REPLACE A
SCRATCHED OR SCORED PISTON.
A. Start from the top down, use the commercially available piston ring expander tool to remove
the two top piston compression rings, the piston oil ring, and the inner expander ring (with
the piston oil ring) (Figure 26).
NOTICE: New cylinders made by Lycoming Engines will have the correct piston ring finish
and do not need further honing. Otherwise, hone the cylinder per the latest revision
of Service Instruction No. SI-1047 to ensure correct seating of the new piston rings.
For new piston rings, refer to the TEO-540-C1A Illustrated Parts Catalog to
identify the correct new piston rings to be installed on the piston.
New piston rings are shipped from Lycoming with the piston oil ring and the inner
expander ring assembled. The inner expander ring must be separated from the piston
oil ring before installing them on the piston.
B. Apply a generous coating of a mixture of 15% pre-lubricant (STP or equivalent) and 85%
SAE 50 mineral-base aviation-grade lubricating oil (unless otherwise directed per the latest
revision of Service Instruction No. SI-1059) to the piston rings.
C. With the piston top side up on a workbench, install the inner expander ring with the part
number facing toward the top of the piston in the first groove above the piston pin hole
(Figure 26).
D. Assemble the piston oil ring over the inner expander ring with its gap 180° opposite the inner
expander ring gap. Orient the gaps in the inner expander ring and piston oil ring
perpendicular to the piston pin hole. Compress the assembly several times with the fingers to
ensure that the ring lies free and loose in the groove. Both the piston oil ring and the inner
expander ring are symmetrical.
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TEO-540-C1A Engine Maintenance Manual
TEO-540-C1A Engine Maintenance Manual
Figure 26
Piston Ring Positions
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November 2018