Piston with lubrication failure
( Ref.: 5, 5A & 5B)
(no signs of detonation on dome)
5 - piston shows scoring marks below the
rings on the intake side.
Possible Cause
Snow or water has entered the engine and destroyed the oil film
if the piston has scoring on the intake and exhaust sides but the
dome shows no signs of abnormal combustion, the engine has been run with too little or no
oil. Check the operation of the oil injection system or the amount of oil in the premixed
fuel. Also, insure proper piston clearance.
if the piston has scoring on the intake and exhaust sides, no
signs of abnormal combustion on the dome and is very dark in color, there has been a
failure of the cooling system. Check the fan belt, or collant level etc.
5a - Piston shows dark brown
deposits all over the skirt.
Possible Cause
wrong oil quality, e.g. gear oil, automotive oil
unnecessary additives have been used in the fuel, i.e. octane boosters, high performance
additives, upper cylinder lubricants, etc.
5B - Piston shows scuffing marks on
the exhaust side of the skirt without corresponding marks on the intake side. The
lubrication film failed under thermal load on the exhaust side of the piston
Possible cause:
Poor quality of oil.
5B
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