C4.2 and C6.4 Engines for Caterpillar Built Machines Engine Valve Lash - Inspect/Adjust Caterpillar

Show/hide table

Be sure the engine cannot be started while this maintenance is being performed. To prevent possible injury, do not use the starting motor to turn the flywheel. Hot engine components can cause burns. Allow additional time for the engine to cool before measuring/adjusting engine valve lash clearance.

The valve lash is measured between the top of the cap of the valve stem and the rocker arm. The valve lash is measured with a feeler gauge.

Valve Lash Setting with Stopped Engine (Cold)

Inlet ... 0.25 mm (0.010 inch)

Exhaust ... 0.40 mm (0.016 inch)

Adjustment of the Height of the Valve Bridge

Show/hide table

Illustration 1	g01410282

1. Push the rocker arm onto the bridge.

2. Loosen the adjustment screw (1) so that the nonadjustable side of the bridge is contacting the valve stem.

3. Tighten the adjustment screw (1) until the adjustment screw (1) contacts the stem.

4. Turn adjustment screw (1) for an additional ten degrees.

5. Tighten locknut (2) to 12 ± 3 N·m (106 ± 27 lb in).

Valve Lash Check

An adjustment is not necessary if the measurement of the valve lash is in the acceptable range in Table 1.

1. Put the No. 1 piston at top center. Refer to Testing and Adjusting, "Finding Top Center Position for No. 1 Piston".
   Show/hide table

   Table 1

   C4.2
   	Inlet Valves	Exhaust Valves
   Valve Lash (Stopped Engine)	0.25 mm (0.010 inch)	0.40 mm (0.016 inch)
   TC Compression Stroke	1-2	1-3
   TC Exhaust Stroke(1)	3-4	2-4
   Firing Order	1-3-4-2(2)

   Show/hide table

   (1)	360° from TC compression stroke
   (2)	The No. 1 cylinder is at the front of the engine.

   Show/hide table

   Table 2

   C6.4
   	Inlet Valves	Exhaust Valves
   Valve Lash (Stopped Engine)	0.25 mm (0.010 inch)	0.40 mm (0.016 inch)
   TC Compression Stroke	1-2-4	1-3-5
   TC Exhaust Stroke(1)	3-5-6	2-4-6
   Firing Order	1-5-3-6-2-4(2)

   Show/hide table

   (1)	360° from TC compression stroke
   (2)	The No. 1 cylinder is at the front of the engine.

If the measurement is not within this range, an adjustment is necessary. Refer to "Valve Lash Adjustment" for the proper procedure.

Valve Lash Adjustment

Use the following procedure to adjust the valve lash.

Show/hide table

Illustration 2	g01425959
Valve lash

1. Ensure that the No. 1 piston is at the top center position on the compression stroke.
   Show/hide table

   Table 3

   C4.2
   TC Compression Stroke	Inlet Valves	Exhaust Valves
   Valve Lash	0.25 mm (0.010 inch)	0.40 mm (0.016 inch)
   Cylinders	1-2	1-3

   Show/hide table

   Table 4

   C6.4
   TC Compression Stroke	Inlet Valves	Exhaust Valves
   Valve Lash	0.25 mm (0.010 inch)	0.40 mm (0.016 inch)
   Cylinders	1-2-4	1-3-5

2. Adjust the valve lash according to Table 3 for C4.2 engines or Table 4 for C6.4 engines.

3. Loosen the adjustment locknut (3).

4. Place the appropriate feeler gauge between rocker arm and the valve bridge. Then, turn the adjustment screw (4) in a clockwise direction. Slide the feeler gauge between the rocker arm and the valve bridge. Continue turning the adjustment screw (4) until a slight drag is felt on the feeler gauge. Remove the feeler gauge.

5. Tighten the adjustment locknut (3) to a torque of 28 ± 7 N·m (248 ± 62 lb in). Do not allow the adjustment screw (4) to turn while you are tightening the adjustment locknut (3). Recheck the valve lash after tightening the adjustment locknut (3).

6. Rotate the engine for 360 degrees in the direction of engine rotation. This will put the No. 6 piston at the top center position on the compression stroke.
   Show/hide table

   Table 5

   C4.2
   TC Exhaust Stroke	Inlet Valves	Exhaust Valves
   Valve Lash	0.25 mm (0.010 inch)	0.40 mm (0.016 inch)
   Cylinders	3-4	2-4

   Show/hide table

   Table 6

   C6.4
   TC Exhaust Stroke	Inlet Valves	Exhaust Valves
   Valve Lash	0.25 mm (0.010 inch)	0.40 mm (0.016 inch)
   Cylinders	3-5-6	2-4-6

7. Adjust the valve lash according to Table 5 for C4.2 engines or Table 6 for C6.4 engines.

8. Loosen the adjustment locknut (3).

9. Place the appropriate feeler gauge between rocker arm and the valve bridge. Then, turn the adjustment screw (4) in a clockwise direction. Slide the feeler gauge between the rocker arm and the valve bridge. Continue turning the adjustment screw until a slight drag is felt on the feeler gauge. Remove the feeler gauge.

10. Tighten the adjustment locknut (3) to a torque of 4 ± 1 N·m (35 ± 9 lb in). Do not allow the adjustment screw (4) to turn while you are tightening the adjustment locknut (2). Recheck the valve lash after tightening the adjustment locknut (3).

Adjusting the valve lash several times in a short period indicates wear in a different part of the engine. Find the problem and make any necessary repairs in order to prevent more damage to the engine.

Rapid wear of the camshaft and tappets can occur if insufficient valve lash is not corrected. Insufficient valve lash can also be an indication of faulty valve seats. The following items are reasons for faulty seats of the valves: faulty fuel injection nozzles, restrictions to the air inlet, dirty air filters, incorrect fuel setting and overloading the engine.

Broken valve stems, broken pushrods, or broken spring retainers can be caused by insufficient valve lash that is not corrected. A fast increase in valve lash can be an indication of any of the following items:

• Worn camshaft and tappets

• Worn rocker arms

• Bent pushrods

• Loose adjustment screws for valve lash

• Broken socket on the upper end of pushrod

Fuel in the lubrication oil may be a possible cause of rapid wear of the camshaft and the tappets. Dirty lubrication oil may also be a possible cause of rapid wear of the camshaft and tappets.