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 TM 55-1905-217-34
(c) Clamp the idler gear assembly and fixture in vise as shown in figure 3-66.
(d) Attach the cord to the idler gear and spring scale and check the pre-load as outlined in item (d) of the first
method.
(9) If the scale reading is within the specified 1/2 to 6-3/4 lbs., but fluctuates more than the permissible 2 lbs. 11
ounces, the idler gear and bearing assembly must NOT be installed on the engine. Fluctuations in scale reading may be
caused by the races not being concentric to each other, damaged races or rollers, or dirt or foreign material within the
bearings. In these cases, the bearing should be inspected for the cause of fluctuation in the scale readings and corrected
or a new bearing installed.
(10) A scale reading which exceeds the specified maximum indicates binding of the bearing rollers, or rollers
improperly installed. The bearing should be disassembled, inspected and replaced, if necessary.
(11) If the scale reading is less than the specified minimum, the bearing is more likely worn. However, the
assembly may be installed on the engine, PROVIDED the gear has no perceptible wobble or shake.
(12) After the pre-load test is completed, remove the steel plates and attach bearing retainer as follows:
(a) Attach the bearing retainer to the idler gear with six bolts and three bolt locks. Tighten the bolts 10 24-29 lb-ft
torque.
(b) Bend the ears of each bolt lock against the flat side of the attaching boltheads to secure the bolts.
NOTE
Idler gear assemblies which have a total length of 1.514" to 1.519" are to be used ONLY on
engines equipped with a cast iron flywheel housing. Idler gear assemblies with a total
length of 1.509" to 1.514" are used on engines with an aluminum flywheel housing and may
also be used with cast iron housings.
g. Installation.
(1) Position the crankshaft gear and either the balance shaft or camshaft gear (depending upon engine rotation) so
that the match marks will align with those on the idler gear.
(2) With these marks in alignment, start the idler gear into mesh with the crankshaft gear and either the camshaft
or balance shaft gear, and simultaneously rotate the gear hub so that the hollow pin at the inner face of the hub nearly
registers with the oil hole in the end plate.
(3) Roll the idler gear into position, align the hollow pin with the hole in the end plate, and gently tap the hub until it
seals against the end plate. Thus the hollow dowel pin in the hub will conduct oil through the end plate and into the hub
where it flows through a drilled passage to the roller bearing.
(4) After making sure that the hub is tight against the end plate, secure the idler gear assembly in place with a /2 "-
13 bolt and special washer. Tighten the bolt to 80-90 lb-ft torque (cast iron cylinder block) or 50-55 lb-ft torque (aluminum
cylinder block).
(5) If previously removed, install the idler gear hole spacer (dummy hub). Secure the spacer to the cylinder block
end plate and cylinder block with a /2 "-13 bolt and special washer. Tighten the bolt to 80-90 lb-ft torque (cast iron cylinder
block) or 50-55 lb-ft torque (aluminum cylinder block).
NOTE
Current engines use a new idler gear hub and idler gear hole spacer (dummy hub) which
required 1/2" - 13 x 2 1/2" retaining bolts, replacing the1/2"- 13 x 2" bolts formerly used.
(6) Lubricate the idler gear and bearing liberally with clean engine oil.
(7) Check the backlash between the mating gears. The backlash must be .003" to .008".
(8) No gasket is used between the roller bearing type idler gear assembly and the flywheel housing. However, if an
OLD design idler gear spacer is used (on early engines), a small flywheel housing gasket must be used between the
spacer and the flywheel housing.
NOTE
Make sure the oil passage in the cylinder block is plugged at the dummy hub location.
(9) If the roller bearing type idler gear assembly has been installed in place of a copper- lead flange type bearing on
an early engine, it will be necessary to rework the flywheel housing at the idler gear hub pads to provide the 7/8" spot faces
at the bolt holes.
(10) Install the flywheel housing..
3-17. Gear Train and Engine Timing
a. General.
(1) A completely enclosed train of five helical gears is located at the rear end of the engine. A gear bolted to the
crankshaft flange drives the camshaft and balance shaft gears, as well as the blower drive gear, through an idler gear
mounted between the crankshaft and balance shaft gears on the RB and LD engines, and between the crankshaft and
camshaft gears on the RD and LB engines. Refer to TM 56-1905-217-12 (para 4-19b).
(2) The camshaft gear and balance shaft gear mesh with each other and run at the same speed as the crankshaft. Since
these two gears must be in time with each other, and the two as a unit in time with the crankshaft gear, the letter "O" is
placed on one tooth of one of the gears with a corresponding mark at the root of the mating teeth of the other gear.
3-89
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