CAT Engine Course (Part 8) Valve Lash

The top bolt in the cover plate of the bore for the engine turning tool is the timing bolt. The timing bolt is used to find the location of No. 1 piston on top center (TC).
This is important to the serviceman because thereference point for all timing proce dures is with No. 1 piston put at top center on the compression stroke.
The pipe plug (arrow) is removed from the flywheel housing to install the timing bolt.

The optional engine turning tool fits in the bore in the flywheel housing and has teeth which engage with the flywheel gear teeth. The engine turning tool is a special tool used for rotation of the crankshaft of the engine when you need to make adjustments, time the engine, or turn an engine in storage.

A 1/2 inch drive ratchet is used to turn the tool and the engine crankshaft.

To find top center compression stroke for No. 1 piston, first turn the flywheel clockwise a minimum of 30 degrees. The reason for making this step is to be sure the backlash is removed from the timing gears when the engine is put on top dead center.

Next, turn the flywheel counterclockwise until the hole in the flywheel is in alignment with the timing bolt. When the timing bolt can be turned freely in the threaded hole in the flywheel, the engine No. 1 piston is on top center.

To check to see if No. 1 piston is on compression stroke, look at the valves of No. 1 cylinder. The valves will be CLOSED if No. 1 cylinder is on compression stroke. You should be able to move the valve rocker arms up and down with your hand.
If No. 1 piston is NOT on compression stroke, turn the crankshaft 360 degrees and follow the procedure again to put No. 1 piston on top center.

With the valve cover removed, we can see the three rocker arm assemblies. The rocker arm on the left (1) activates the bridge and the two exhaust valves. The center rocker arm (2) activates the unit injector for fuel injection. The rocker arm on the right (3) activates the bridge and the two inlet (intake) valves.

NOTE: On production engines, lower thread bosses are removed. EXHAUST and INTAKE are stamped on housing.

The valve arrangement is the same as other engine valvesactivated by push rods, except a valve bridge. The bridge activates the two inlet valves or exhaust valves at the same time (similar to the 3400 Series Engines). The bridge fits on a dowel which is the guide when the bridge moves up and down. The bridge is moved (activated) by the rocker arm. Adjustment of the valve bridge is done when the engine is assembled and when valve lash adjustment is made.

To adjust the bridge, loosen the locknut, push down on the rocker arm (or point of contact) and turn the adjustment screw clockwise until it contacts the stem of the valve. Turn the adjustment screw an additional 20 to 30 degrees (1/3 to 1/2 of one side of the nut) to position the guide of the bridge straight on the dowel.
Tighten the locknut to specifications.

NOTE: Normally, adjustment of the bridge will be donewith the rocker arm assembly off the cylinder head.

Valve clearance or valve lash is measured with a feeler gauge or 8T5207 setting gage, put between the rocker arm contact and the bridge wear seat. Valve clearance is changed using a screwdriver.

A 3/4 inch wrench is needed to loosen and tighten the locknut which holds the adjustment screw. To make the adjustment, turn the adjustment screw until you feel an easy pull on the feeler gauge as you move it backward and forward between the rocker arm contact and the bridge wear seat. Tighten the nut on the adjustment screw and check the adjustment to be sure it has not changed. The adjustment of all valves and the injectors can be done by putting the engine crankshaft in two positions. Refer to the Service Manual for these procedures.


valves said…
Your article is amazing. It helped me a lot with my research about different kinds of valves and actuators and how this stuff works with other mechanical devices...

again,thanks a lot.

Raghav said…
HI, graeat blog vey informative. I am looking for a engine turning device / stand . would anyone know where I can procure this in India.
raghav mallik

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