Engine Timing - TM-55-1905-217-340118

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Installation

TM-55-1905-217-34 Landing Craft Mechanized; Steel; DED; Overait Length 74 Feet Mod 1 Marl VIII Navy Design LCM-8 Manual

Figure 3-67. Gear train and timing marks- left-hand rotation engines.

TM 55-1905-217-34

(3) The camshaft and balance shaft gears are keyed to their respective shafts and held securely against the

shoulder on the shaft by a nut. Viewing the engine from the flywheel or gear train end, the righthand gear, whether on the

balance shaft, as shown on RD and LD engines, or the camshaft, as shown on RB and LB engines, has left-hand helical

teeth.

(4) The idler gear rotates on a double-row, tapered roller bearing mounted on a stationary hollow hub. This hub is

accurately located on the cylinder block end plate, at the right-hand side of the LB and LD engines and at the left-hand side

of the RB and RD engines, as viewed from the gear train end.

(5) A blower drive gear is located on the blower side to transmit power to the blower, governor, fuel pump and water

pump.

(6) Since, as stated above, the cam and balance shafts must be in time with the crankshaft, identification marks

are located on two teeth of the idler gear with corresponding match marks stamped on the crankshaft gear and the

camshaft or balance shaft gear.

(7) Gear train noise is usually an indication of excessive gear lash, scoring, pitting or excessive bearing wear.

Therefore, when noise develops in a gear train, the flywheel housing should be removed and the gear train and its bearings

inspected. A rattling noise usually indicates excessive gear lash whereas a whining noise is a result of too little gear lash.

(8) Excessive wear and scoring may result from abrasive substances or foreign material in the oil, introduced in the

engine by such means as removal of the rocker cover without first cleaning away the dirt.

(9) The backlash between the various mating gears in the current 19helix steel gear train ranges from .003 inch to

.008 inch with new parts.

b. Engine Timing.

(1) The correct relationship between the crankshaft and camshaft must be maintained to properly control fuel

injection and the opening and closing of the exhaust valves.

(2) The crankshaft timing gear can be mounted in only one position due to one attaching bolt hole being offset. The

camshaft gear can also be mounted in only one position as a result of the location of the keyway relative to the cams.

Therefore, when the engine is properly timed, the markings on the various gears will match as shown in figures 3-67 and

3-68.

3-90