ENGINE
A. Vertical scratches that appear all the way
around the piston sometimes is combined with
discoloration (see Figure 76). Scratches all the
way around the piston indicate high hours or
dirt ingestion. If the scratches are in limited
areas, look more closely to see if they are in
line with the ports. On a NEW engine, if the
ports are not properly deburred, piston damage
can result. This can appear ONLY on engines
with very few hours on them. The damage is
immediate. If the engine has more than a
couple of hours use, inspect the carburetor,
reed area, and crankcase for any sign of dirt.
Much of the dirt that an engine ingests does its
damage and goes out the exhaust. Any dirt
found in these areas indicate that the engine
has ingested a great deal more. If an engine
has ingested dirt, the best solution is a short
block replacement as the bearings have been
exposed to that dirt also.
C. Cylinder damage is usually less than the
damage to the piston. As the cylinder liner is
made of harder material, it can stand more
abrasion. However, it is generally best to
replace the short block if severe piston damage
is present, as it is the most cost-effective repair.
Reed Valve Service
(DuraForce Engines Only)
The reed assemblies (see Figure 77) permit fuel
mixtures to enter the crankcase on compression
strokes and to trap fuel mixtures in the crankcase on
power strokes.
Figure 77
0720-018
1.
2.
Check clearance between tip of reed and plate;
replace reeds if clearance is more than .020"
(.5
mm).
Figure 76
0893-027
CAUTION: Do not use compressed air to clean
reeds.
B. Discoloration of a piston is often caused by
improper lubrication. Without the necessary
lubrication, friction increases and overheats the
piston. Often in an engine that failed due to
improper lubrication, the piston is discolored,
the rings may be stuck, yet the lower rod and
crankshaft bearings might appear usable. As
the piston is the source of the friction and heat,
the bearings, further from the heat source, may
not appear damaged. However, we would not
recommend re-using bearings in an engine that
failed due to improper lubrication.
Clean reeds carefully, by hand, using carburetor
solvent.
43
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