Service Manual
43
ENGINE
A. Vertical scratches that appear all the way
around the piston sometimes is combined with
discoloration (see Fi
g
ure 76). Scratches all the
way around the piston indicate hi
g
h hours or
dirt in
g
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
g
ine, if the
ports are not properly deburred, piston dama
g
e
can result. This can appear ONLY on en
g
ines
with very few hours on them. The dama
g
e is
immediate. If the en
g
ine has more than a
couple of hours use, inspect the carburetor,
reed area, and crankcase for any si
g
n of dirt.
Much of the dirt that an en
g
ine in
g
ests does its
dama
g
e and
g
oes out the exhaust. Any dirt
found in these areas indicate that the en
g
ine
has in
g
ested a
g
reat deal more. If an en
g
ine
has in
g
ested dirt, the best solution is a short
block replacement as the bearin
g
s have been
exposed to that dirt also.
Fi
g
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
g
ine that failed due to
improper lubrication, the piston is discolored,
the rin
g
s may be stuck, yet the lower rod and
crankshaft bearin
g
s mi
g
ht appear usable. As
the piston is the source of the friction and heat,
the bearin
g
s, further from the heat source, may
not appear dama
g
ed. However, we would not
recommend re-usin
g
bearin
g
s in an en
g
ine that
failed due to improper lubrication.
C. Cylinder dama
g
e is usually less than the
dama
g
e to the piston. As the cylinder liner is
made of harder material, it can stand more
abrasion. However, it is
g
enerally best to
replace the short block if severe piston dama
g
e
is present, as it is the most cost-effective repair.
Reed Valve Service
(DuraForce Engines Only)
The reed assemblies (see Fi
g
ure 77) permit fuel
mixtures to enter the crankcase on compression
strokes and to trap fuel mixtures in the crankcase on
power strokes.
Fi
g
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
g
carburetor
solvent.