Home> Continental & Lycoming TroubleShoot
Oil in Combustion Chamber. Related problem oil in intake.
 Top
of piston shouldn't look wet! Too much oil in the combustion chamber.
A cylinder that is not firing will have oil in the combustion chamber. Without
proper combustion pressures the rings do not operate properly.
1. Past piston rings.
2. Past intake guide. Uncommon in Lycoming engines.
In the Continental C85 O200 O300 aircraft engine oil can end up in the induction
system and the combustion chamber if an exhaust rocker arm has been installed in
the intake position. In these engines only the exhaust rocker arm has an oil
squirt. When the exhaust rocker arm is mistakenly placed on the intake side the
oil spray gets sucked down the intake guide into the induction system and the
combustion chamber.
3. Through induction system. Leaking turbocharger seals. Remove intake
tubes and wash out oil. Re-install and run engine for short period. Remove
intake tube and see whether oil is traveling from turbo to cylinder or
visa versa. Oil in the exhaust system upstream of the turbocharger indicates
malfunction such as problems with rings, pistons, or valves. If engine
idles too slow, turbo does not turn allowing oil to leak from compressor
seal. Leak in compressor seal can be caused by:
(a) air cleaner element clogged or restriction in duct between air
cleaner and turbocharger which can cause oil to be drawn past the turbocharger
seal at the compressor end,
(b) restriction or faulty check valve in turbocharger oil drain line,
which may raise the oil level in the turbocharger center housing and cause
seal leakage,
(c) malfunction in oil scavenge pump,
(d) restriction in aircraft engine crankcase breather,
(e) worn or damaged compressor wheel,
(f) turbocharger shaft bearings or bearing bores worn,
(g) crankcase pressurization causing back-pressure into oil drain line
due to piston blowby.
4. Plugged fuel injector nozzle. The lack of fuel and combustion pressure
allows the oil to bypass piston rings, thereby giving a false impression
of ring problems.
5. Cylinder not firing. Check ignition system. Also, check for air leak into
induction system that is causing the engine to misfire.
6. Poor piston ring performance. Inspect cylinder wall for "bore polishing".
If the bore is worn smooth so that it shines like a mirror then the rings
will allow excessive oil into the combustion chamber. Remove and repair
cylinder wall.
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Sacramento Sky Ranch Inc. All rights reserved.
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