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TM 5-3805-255-14
OPERATOR, FIELD, AND SUSTAINMENT MAINTENANCE
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THEORY OF OPERATION
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ENGINE
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Description
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The 817 Series C diesel engine is a heavy-duty, high-speed, direct-starting, four-cycle, valve-in-head design using
a 24VDC starting system and direct fuel injection.
The crankshaft is fully counterbalanced. It is supported by seven steel-backed, tri-metal type main bearings with
rear bearing, No. 7, absorbing crankshaft end thrust. The connecting rod bearings are also of steel-backed, tri-
metal type.
The camshaft is supported by seven bearings with thrust being taken on front bearing. The bearings are steel
shells, solid or split, with babbit bearing material. The camshaft has two lobes per cylinder, one each for exhaust
and intake valves. The camshaft is driven directly from the crankshaft gear.
The aluminum-alloy, tin-plated, solid-skirt pistons are cam ground, and are fitted with two compression and one oil-
control ring. The full-floating type piston pins are held in place by snap rings at the ends of each pin. The under-
surfaces of the piston crowns are jet-cooled by lubricating oil. Forged steel connecting rods contain a bronze
bushing at the upper end for installation on the piston pin, while the lower end and cap contain the locking type
precision fit bearing inserts.
There are two cylinder heads, each covering three cylinders. There are two intake and two exhaust valves per
cylinder. Each pair of valves is actuated by a rocker arm and guided bridge.
Bridges have an adjustment at one end to ensure even contact with both valves. Positive-type rotators are used on
all intake and exhaust valves. Replaceable valve seat inserts are used on exhaust valves. Positive valve rotators
and valve seat inserts are used on all valves.
The cylinder sleeves are replaceable, wet type. Three O-rings, located in grooves at the lower end of the sleeve,
provide an effective seal between the cylinder sleeve, crankcase, and the water jacket surrounding it.
The full-pressure lubrication system assures positive lubrication to all working parts. A gear-type oil pump is exter-
nally mounted to the left side of the crankcase. Oil is drawn from the oil pan by the pump and is distributed under
pressure though rifle-drilled passages in the crankcase and crankshaft.
Piston cooling jets (located on the right side of crankcase) spray each piston with 1.5 gal. (5.7 L) of oil per minute.
Coolant is circulated through the engine and radiator by a centrifugal water pump mounted on a common shaft with
the lubricating pump. Two thermostats, located in the water outlet header, control coolant temperature in the
system.
The fuel system consists of fuel lines, fuel filters, injection pump, injection nozzles, and lines.
There are three fuel injection nozzles in each cylinder head, one between each pair of intake and exhaust valves.
To insure efficient cooling, nozzles are inserted into a thin-walled copper tube, passing through water space in
cylinder head.
The rocker arm assembly on each head is mounted on four brackets and is located and held down by cylinder
head suds and nuts. There are two rocker levers per cylinder, one for each pair of intake exhaust valves. A valve
bridge connects each pair of intake and exhaust valves which allows both valves to be actuated by one rocker
lever.
Both cylinder heads are basically of uniform construction, however, slight modifications in design prevent them
from being interchangeable. A separate cylinder head gasket with integral gasket rings is provided for each head.
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