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Home> Continental & Lycoming TroubleShoot
Exhaust valve leakage in Lycoming or Continental aircraft engines - causes Continental
exhaust valve, seat and guide
1. Worn exhaust guide. Guide pilots the valve onto the seat. When the guide wears it allows the valve to contact the seat off- center. 2. Stuck valve. A sticky valve may not completely close. 3. Improper grinding of the seat face. 4. Improper grinding of the valve face. 5. Valve or seat warpage. 6. Broken valve face. 7. Deposits on seat face preventing valve sealing. 8. Poor alignment between guide and seat. 9. Insufficient dry tappet clearance. See Checking and Adjusting Dry Tappet Clearance on Lycoming Engines
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Copyright 2003 by
Sacramento Sky Ranch Inc. All rights reserved. Prices subject to
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Lycoming
exhaust valve. Damage from flying with a leaking exhaust valve. Notice missing
pieces.
Common cause
of exhaust leak. Notice the width of the seat where the dark lines are. To the
left it is narrow and to the right it is wide. The seat is not centered to the
guide so that the grinding stone used to grind the seat face ground more on the
left than on the right. More stone pressure was on the left. When you install
the valve the same thing happens--more seat pressure occurs on the left hand
side than on the right. Leakage occurs on the right hand side where the valve
seating pressure is less. This is an example of how poor machining is the most
common reason exhaust valves leak --not leaning or pilot technique. To fix this
problem you need to move the seat to the left or move the guide to the right.
Very few shops can move the holes around as it requires expensive jigs. Just
putting in a new seat and guide will only temporarily fix the problem.