Crankshafts And Camshafts - Tecumseh ECV100-120 - TECHNICIAN S Handbook

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.
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37
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39