Custom Search
 
  
 
TM 55-1905-220-14-8
4-7.10A. ENGINE - MAINTENANCE INSTRUCTIONS (Continued)
ENGINE OVERHAUL (Cont)
b. Piston Burn-thru.
If a hole is burned right through the piston, look for an improperly adjusted carburetor or incorrect timing.
If these items check out OK, check use of wrong oil or improperly mixed fuel. The wrong type of spark plug for
conditions involved may also be the cause of abnormally high combustion temperatures which cause burn-thru.
Use Champion RN-3 spark plugs.
c. Foreign Material.
CAUTION
When inspecting spark plugs, clean out around spark
plug openings before removing plugs. Otherwise,
damage can result from foreign objects dropping into
the engine. If the damage is on the piston crown,
something probably fell into the opening when the
plug was removed. Damage on the sides of piston may
indicate that an object was drawn into the intake.
d. Loose Needle, Retainers, Pins.
Piston and cylinder damage caused by loose needle bearings, pin retainers, or piston pins is usually quite
easy to diagnose. A needle bearing is hard enough to cut right through piston rings without leaving jagged
edges - a loose retainer will not cut but will break the ring. If retainer falls out or is not installed in the first
place, the pin may rub a regular groove in the cylinder wall. Often damage such as this goes by unnoticed until
power becomes extremely poor due to lack of compression.
e. Ring Breakage.
If a ring breaks, the engine may continue running; however, it will probably back-fire badly and it cannot
be restarted after it is shut down. Ring breakage occurs from overheating due to lack of proper lubrication. A
poor quality or wrong type of oil may have been used or the oil may have been poorly mixed or mixed in
incorrect proportion with the gasoline. A ring that has been subjected to overheating often becomes soft and is
easily bent.
f. Rings Sticking.
If there has been repeated occurrence of spark plug fouling, the rings might be stuck in the grooves due
to carbon fouling. This usually occurs from an "over-rich" fuel mixture. If the build-up is varnish rather than
carbon, this probably indicates use of an unauthorized lubricating oil.
4-391


 


Privacy Statement - Copyright Information. - Contact Us

Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business