C3.8 Engines for Caterpillar Built Machines Caterpillar

Gear Group (Front) - BL21-Up, MD21-Up, BL71-Up, HP21-Up, FD21-Up, DX21-Up

Usage:

Show/hide table




Illustration 1	g02974221
(1) Fan Drive Pulley (2) Crankshaft Bolt (3) Gear Case Cover

Show/hide table

Table 1
Tightening torque	Crankshaft bolt	255 to 274 N·m (188 to 202 lb ft)
Tightening torque	Gear case cover mounting bolts	24 to 27 N·m (18 to 20 lb ft)

Relief Valve

Show/hide table




Illustration 2	g02915717
(1) Relief Valve (2) Packing (3) Spring

Show/hide table

Table 2
Tightening torque	Relief valve	69 to 78 N·m (51 to 57 lb ft)

Idler Gear 1

Show/hide table




Illustration 3	g03853284
(1) Idler Gear 1 (2) Idler Gear 1 Mounting Bolts

Show/hide table

Table 3
Tightening Torque	Idler Gear 1 Mounting Bolts	24 to 27 N·m (18 to 20 lb ft)

Idler Gear 3

Show/hide table




Illustration 4	g03853569
(1) Supply Pump Gear (2) Supply Pump Gear Mounting Nut (3) Idler Gear 3 Holder (4) Idler Gear 1 (5) Mounting Screw and Nut

Show/hide table

Table 4
Tightening Torque	Idler Gear 3 Mounting Screw and Nut	24 to 27 N·m (18 to 20 lb ft)

Camshaft Gear

Show/hide table




Illustration 5	g02975218

Show/hide table




Illustration 6	g02915777
(1) Camshaft Set Screw (2) Camshaft Pulsar Gear Set Screw

Show/hide table

Table 5
Tightening torque	Camshaft set screw	24 to 27 N·m (18 to 20 lb ft)
Tightening torque	Camshaft pulsar gear screw	4.7 to 5.6 N·m (3.5 to 4.1 lb ft)

Timing Gear Backlash

Show/hide table




Illustration 7	g03854101
(1) Supply Pump Gear (2) Idler Gear 3

Show/hide table




Illustration 8	g03854102
(3) Camshaft Gear (4) Idler Gear 1 (5) Crankshaft Gear

Show/hide table

Table 6
Backlash between crankshaft gear and Idler Gear 1	Factory specification	0.0490 to 0.193 mm (0.00193 to 0.00759 inch)
Backlash between crankshaft gear and Idler Gear 1	Allowable limit	0.22 mm (0.0087 inch)

Show/hide table

Table 7
Backlash between Idler Gear 1 and camshaft gear	Factory specification	0.0490 to 0.189 mm (0.00193 to 0.00744 inch)
Backlash between Idler Gear 1 and camshaft gear	Allowable limit	0.22 mm (0.0087 inch)

Show/hide table

Table 8
Backlash between Idler Gear 1 and Idler Gear 3	Factory specification	0.0490 to 0.162 mm (0.00193 to 0.00637 inch)
Backlash between Idler Gear 1 and Idler Gear 3	Allowable limit	0.22 mm (0.0087 inch)

Show/hide table

Table 9
Backlash between Idler Gear 3 to supply pump gear	Factory specification	0.054 to 0.167 mm (0.00213 to 0.00657 inch)
Backlash between Idler Gear 3 to supply pump gear	Allowable limit	0.22 mm (0.0087 inch)

Side Clearance of Idler Gears

Show/hide table




Illustration 9	g02915876

Note: The Illustration is a representation and is not the actual configuration.

Set a dial indicator with its point on the Idler Gear 1.
Move the Idler Gear 1 to the front and rear to measure the side clearance.
Show/hide table
Table 10
Side clearance of Idler Gear 1 Factory specification 0.15 to 0.30 mm (0.0059 to 0.011 inch)

Allowable limit 0.90 mm (0.035 inch)

Show/hide table
Table 11
Side clearance of Idler Gear 3 Factory specification 0.10 to 0.40 mm (0.0039 to 0.016 inch)

Allowable limit 0.90 mm (0.035 inch)
If the measurement is more than the allowable limit, replace the Idler Gear 1 collar.

Table 10
Side clearance of Idler Gear 1	Factory specification	0.15 to 0.30 mm (0.0059 to 0.011 inch)
Allowable limit	0.90 mm (0.035 inch)

Table 11
Side clearance of Idler Gear 3	Factory specification	0.10 to 0.40 mm (0.0039 to 0.016 inch)
Allowable limit	0.90 mm (0.035 inch)

Oil Clearance between Idler Gear Shaft 1 and Idler Gear 1 Bushing

Show/hide table




Illustration 10	g02973422

Measure the Idler Gear shaft outside diameter with an external micrometer.
Show/hide table

Illustration 11 g02973488
Measure the Idler Gear bushing inside diameter with an internal micrometer.
Calculate the oil clearance.

Show/hide table

Table 12
Oil clearance between Idler Gear shaft 1 and Idler Gear 1 bushing	Factory specification	0.050 to 0.091 mm (0.0020 to 0.0035 inch)
	Allowable limit	0.10 mm (0.0039 inch)

Show/hide table

Table 13
Idler Gear 1 bushing inside diameter	Factory specification	45.025 to 45.050 mm (1.7727 to 1.7736 inch)
Idler Gear shaft 1 outside diameter	Factory specification	44.959 to 44.975 mm (1.7701 to 1.7706 inch)

Show/hide table




Illustration 12	g03854287
Checking Idler Gear 3 holder ID and Idler Gear 3 OD

Show/hide table

Table 14
Oil clearance between Idler Gear 3 and Idler Gear 3 holder	Factory specification	0.016 to 0.61 mm (0.00062 to 0.024 inch)
Oil clearance between Idler Gear 3 and Idler Gear 3 holder	Allowable limit	0.10 mm (0.0039 inch)

Show/hide table

Table 15
Idler Gear 3 holder inside diameter	Factory specification	16.000 to 16.018 mm (0.63 inch)
Idler Gear 3 outside diameter	Factory specification	15.957 to 15.984 mm (0.63 inch)

Note: If the oil clearance is more than the allowable limit, replace the bushing.