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High wear metals in aircraft oil sampling - chrome
1. From cylinder walls. Check to see if you have chrome cylinder barrels.
Boroscope cylinder. Chrome from cylinder walls can be caused by seizing
of rings or piston onto barrel, mechanical abrasion from failed piston
assembly, or excessively rough chrome surface. An excessively rough chrome
surface will abrade a penny dragged across the surface. Rough chrome will
lock the piston rings in place preventing ring movement or rotation. There
will be a fine dark line down the cylinder barrel where the ring gap was
located against the barrel surface.
2. From piston rings. Fatigue failure of ring surface will cause small
flakes of chrome plating to separate from the ring surface. This failure
is caused by an excessively rough or pitted cylinder barrel. 3. From exhaust valve stem. Continental engines with Nitralloy exhaust
valve guides would occasionally strip chrome from valve stem. Note: Nitralloy
exhaust guides have been discontinued in Continental engines and are not
currently used although there are still many operating engines using these
guides. High levels of chrome in aircraft oil samples is somewhat unusual. Chrome produces flakes that
often don't end up in oil samples since they settle out in the oil sump.
 Close-up
of chrome cylinder barrel sometimes called "channelchrome".
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