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Cam Shaft Shims: Cam shaft shims serve two purposes.
First, they are used to adjust the side play, or lateral movement of the cam shaft between
the right side engine case and the gear cover. Second, they provide a thrust surface between
the cam gear and the face of the bronze cam bushing. Early 45s used fiber shims which had a
tendency to fail in service and are still available, but are not advised.
Later 45s were fitted at the factory with steel shims.
0.006” thick cam shaft shims should be placed on the inboard side of each cam shaft, behind
the cam gear. The cam shafts are then installed in the right side crank case and the gear
cover installed. The gear cover should be installed with the gear cover gasket then all
screws fully tightened. The lateral movement of each cam shaft is then measured to determine
the size required of each outboard cam shim. Note that only cam shafts no. 1, 2 & 3 receive
outboard shims because the outer face of the no. 4 cam shaft thrusts against the oil pump housing.
If the engine is disassembled, the side play can be measured from the inside of the crank case using a dial indicator, moving the cam shafts back and forth through the tappet guides.
If the engine is assembled, tappet guides will need to be removed and side play measured using feeler
gauges between the inner face of the cam lobe and the outer face of the cam shaft bushing.
Cam shaft side play should be between “free running” and 0.006”. Measure and record the side play of
each cam shafts without outboard shims. From this measurement, subtract the amount of allowable play
to determine the shim required. For example, if we measure 0.020” side play with only the inboard shim,
then subtract 0.006”, we need a 0.014” shim. Adding a 0.015” shim will result in 0.005” clearance, which
is within the acceptable range.
If for some reason one or more of the cam shafts bind with only a 0.006” inboard shim and the cam cover
with gasket fully tightened, we can either replace all four inboard shims with thinner ones, or use a
thicker gasket.
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