C12 Marine Engine Caterpillar

Engine Valve Lash - Inspect/Adjust

Usage:

C-12 9HP

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To prevent possible injury, do not use the starter to turn the flywheel.

Hot engine components can cause burns. Allow additional time for the engine to cool before measuring valve clearance.

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This engine uses high voltage to control the fuel injectors.
Disconnect electronic fuel injector enable circuit connector to prevent personal injury.

Do not come in contact with the fuel injector terminals while the engine is running.

Note: Valve lash is measured between the rocker arm and the valve bridge. All measurements and adjustments must be made while the engine is stopped and the valves are fully closed.

Valve Lash Check

An adjustment is NOT NECESSARY if the measurement of the valve lash is in the acceptable range in Table 1.

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Table 1
Valve Lash Check (Stopped Engine)
Inlet	0.30 to 0.46 mm (0.012 to 0.018 inch)
Exhaust	0.56 to 0.72 mm (0.022 to 0.028 inch)

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

Valve Lash Adjustment

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Illustration 1	g00280040
(A) Exhaust valves (B) Inlet valves

Use the following procedure to adjust the valve lash:

Put the No. 1 piston at the top center position on the compression stroke. Refer to Testing and Adjusting, "Finding Top Center Position for No. 1 Piston".

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Illustration 2	g00481639
Adjustment of the inlet valve (1) Inlet rocker arm (2) Adjustment locknut

Adjust the valve lash on the inlet valves for cylinders 1, 2, and 4.
1. Lightly tap the rocker arm at the top of the adjustment screw with a soft mallet. This will ensure that the lifter roller seats against the camshaft's base circle.
1. Loosen adjustment locknut (2) .
1. Place the appropriate feeler gauge between inlet rocker arm (1) and the inlet valve bridge. Then, turn the adjustment screw 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.
1. Tighten adjustment locknut (2) to a torque of 30 ± 7 N·m (22 ± 5 lb ft). Do not allow the adjustment screw to turn while you are tightening the adjustment locknut. Recheck the valve lash after tightening the adjustment locknut.

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Illustration 3	g00481645
Adjustment of the exhaust valve (3) Exhaust rocker arm (4) Adjustment locknut

Adjust the valve lash on the exhaust valves for cylinders 1, 3, and 5.
1. Lightly tap the rocker arm at the top of the adjustment screw with a soft mallet. This will ensure that the lifter roller seats against the camshaft's base circle.
1. Loosen adjustment locknut (4) .
1. Place the appropriate feeler gauge between exhaust rocker arm (3) and the exhaust valve bridge. Then, turn the adjustment screw 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.
1. Tighten adjustment locknut (4) to a torque of 30 ± 7 N·m (22 ± 5 lb ft). Do not allow the adjustment screw to turn while you are tightening the adjustment locknut. Recheck the valve lash after tightening the adjustment locknut.

Remove the timing bolt and turn the flywheel by 360 degrees in the direction of engine rotation. This will put the No. 6 piston at the top center position on the compression stroke. Install the timing bolt in the flywheel.

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Illustration 4	g00481639
Adjustment of the inlet valve (1) Inlet rocker arm (2) Adjustment locknut

Adjust the valve lash on the inlet valves for cylinders 3, 5, and 6.
1. Lightly tap the rocker arm at the top of the adjustment screw with a soft mallet. This will ensure that the lifter roller seats against the camshaft's base circle.
1. Loosen adjustment locknut (2) .
1. Place the appropriate feeler gauge between inlet rocker arm (1) and the inlet valve bridge. Then, turn the adjustment screw 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.
1. Tighten adjustment locknut (2) to a torque of 30 ± 7 N·m (22 ± 5 lb ft). Do not allow the adjustment screw to turn while you are tightening the adjustment locknut. Recheck the valve lash after tightening the adjustment locknut.

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Illustration 5	g00481645
Adjustment of the exhaust valve (3) Exhaust rocker arm (4) Adjustment locknut

Adjust the valve lash on the exhaust valves for cylinders 2, 4, and 6.
1. Lightly tap the rocker arm at the top of the adjustment screw with a soft mallet. This will ensure that the lifter roller seats against the camshaft's base circle.
1. Loosen adjustment locknut (4) .
1. Place the appropriate feeler gauge between exhaust rocker arm (3) and the exhaust valve bridge. Then, turn the adjustment screw 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.
1. Tighten adjustment locknut (4) to a torque of 30 ± 7 N·m (22 ± 5 lb ft). Do not allow the adjustment screw to turn while you are tightening the adjustment locknut. Recheck the valve lash after tightening the adjustment locknut.