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 TM 55-1905-219-14-5
3-91.5. CAMSHAFT AND BALANCE SHAFT - MAINTENANCE INSTRUCTIONS.
a. The camshaft and the balance shaft are located near the top of the cylinder block. The camshaft
actuates the valve and injector operating mechanism.
b. The accurately ground cams on the camshaft ensure efficient, quiet cam follower roller action and are
heat treated to provide a hard wear surface.
c. The engine is equipped with a low velocity, low lift injector cam lobe and a long closing ramp exhaust
cam lobe design camshaft and can be identified by the numeral "7" stamped on one end., is serviced.
d. Both ends of the cam and balance shaft are supported by bearing assemblies, each consisting of a
flanged housing and two bushings. In addition, intermediate two-piece bearings support the camshaft at uniform
intervals throughout its length. The intermediate bearings are secured to the camshaft by lock rings, thereby
permitting them to be inserted into the cylinder block with the shaft. Each intermediate bearing is secured in
place, after the camshaft is installed, with a lock screw threaded into a counter bored hole in the top of the
cylinder block.
e. On both the camshaft and the balance shaft, the gear thrust load is absorbed by two thrust washers.
The thrust washers bear against thrust shoulders on the shafts.
f. A helical drive gear with a counterweight is secured to each shaft with a Woodruff key, nut, nut
retainer, retainer bolts and lock washers. The drive gears are attached to the rear end of the shafts on all
engines.
g. To help maintain engine balance, a balance weight is installed on the front end of each shaft.
h. Lubrication.
(1) Lubricating oil is supplied under pressure to the bearings from the longitudinal main oil gallery
through a horizontal transverse passage at each end of the cylinder block, then up the connecting vertical
passages in each corner of the block ,to the camshaft and balance shaft end bearings. The camshaft
intermediate bearings are lubricated by the oil from the end bearings passing through the drilled passage in the
shaft.
(2) The lower halves of the camshaft intermediate bearings are grooved along the horizontal surface that
mates with the upper halves of the bearings. Oil from the passage in the camshaft is forced through the milled
slots in the bearing and then out the grooves to furnish additional oil to the cam follower assemblies. This perits
the cam pocket to be filled rapidly to the operating oil level immediately after starting the engine.
3-1590
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