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