Specifications

84
36
37
CRANKSHAFTS AND CAMSHAFTS
Inspect the crankshaft visually and with a micrometer for
wear, scratching, scoring, or out of round condition. Check
for bends on the P.T.O. end using a straight edge, square
or a dial indicator.
CAUTION: NEVER TRY TO STRAIGHTEN A
BENT CRANKSHAFT.
The timing marks on the camshaft and the crankshaft gears
must be aligned for proper valve timing. (diag. 36 & 37).
Camshafts
Check the camshaft bearing surfaces for wear using a
micrometer. Inspect the cam lobes for scoring or excessive
wear. If a damaged camshaft is replaced, the mating
crankshaft and governor gear should also be replaced. If
the crankshaft gear is pressed on it is not serviceable and
the crankshaft must also be replaced.
Clean the camshaft with solvent and blow all parts and
passages dry with compressed air, making sure that the
pins and counterweights are operating freely and smoothly
on mechanical compression relief types.
Camshafts used in rotary mower engines utilize a composite
gear (glass filled nylon) for the purpose of reducing internal
gear noise.
Mechanical Compression Release (MCR) camshafts have
a pin located in the camshaft, that extends over the exhaust
cam lobe, to lift the valve and relieve the engine compression
for easier cranking. When the engine starts, centrifugal
force moves the weight outward and the pin will drop back
down. The engine will now run at full compression (diag.
38).
Some engines are equipped with Bump Compression
Release (BCR) camshafts that have a small bump ground
on the exhaust lobe of the camshaft to relieve compression
(diag. 39).
Newer camshafts are designated as Ramp Compression
Release (RCR) and utilize a less aggressive ramp than
what is used on the BCR camshaft.
LEV Exhaust Mechanical Compression
Release (MCR) Cam Bushing Service
(Used in production October 1999)
Removal
1. Place an LEV cylinder in a soft jawed vice and using a
nonmetallic mallet, tap a #6 easy-out into the bushing
so the easy-out makes a solid contact with the cam
bushing.
2. Turn counterclockwise until the easy-out goes into the
bushing a sufficient amount so that the bushing can be
removed without the easy-out releasing. Spin the
bushing counterclockwise with the easy-out while pulling
for removal. CAUTION: Cam bushings should never be
reused.
3. Blow compressed air down the top main bearing oil
galley to the top cam bearing. This will clean any plastic
particles that might have entered into the passage from
the cam bushing removal procedure. Rinse cylinder in
a parts tank, then lubricate the cam bearing pocket
with oil.
GEAR
KEYWAY
CAMSHAFT
GEAR
SMALL
HOBBING HOLE
PUNCH MARK
CRANKSHAFT GEAR
CAMSHAFT
GEAR TIMING
MARK
CHAMFER TOOTH
BEVEL
SMALL HOBBING
HOLE
CRANKSHAFT
38
39
INTAKE
EXHAUST
COMPRESSION
RELEASE
MECHANISM
CAM
BUSHING
INSTALLED
40
AIR FROM
TOP MAIN
BEARING
OIL GALLEY
Þ