3116 and 3126 Truck Engines Valve Lash Adjustment

Valve adjustment in 3116 and 3126 diesel engines is an important maintenance procedure that ensures the proper functioning of the engine and prevents issues like poor performance, excessive fuel consumption, and engine damage. Valve adjustment involves setting the clearance (also known as lash) between the valve stem and the rocker arm or camshaft. This clearance can change over time due to wear and tear, and it needs to be periodically adjusted to maintain optimal engine performance.

To adjust the valves on a 3126 engine, you will need the following tools:

• Feeler gauges
• 10mm wrench
• 13mm wrench
• 19mm wrench
• 24mm wrench
• Screwdriver

Instructions:

1. Disconnect the negative battery cable.
2. Remove the valve cover.
3. Locate the cylinder that is at the top of its compression stroke. You can do this by looking at the rocker arms. The rocker arm for the intake valve will be loose, and the rocker arm for the exhaust valve will be tight.
4. Use the feeler gauge to check the clearance between the rocker arm and the inlet valve.
5. If the clearance is not within the specified range, adjust it by turning the screw on the rocker arm clockwise to tighten the clearance or counterclockwise to loosen the clearance.
6. Once the clearance is adjusted, tighten the locknut on the rocker arm.
7. Repeat steps 4-6 for the exhaust valve.
8. Move to the next cylinder and repeat steps 4-7 until all of the valves have been adjusted.
9. Reinstall the valve cover and tighten the bolts.
10. Reconnect the negative battery cable.

Valve Lash Check

An adjustment is not necessary if the measurement of the valve lash is in the acceptable range. Adjust the valve lash while the engine is stopped. The range is specified in Table 1.

Table 1

	Inlet Valves	Exhaust Valves
Valve Lash Check (Stopped Engine)	0.38 ± 0.08 mm (0.015 ± 0.003 inch)	0.64 ± 0.08 mm (0.025 ± 0.003 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)

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

Valve lash is measured between the rocker arm and the valve. All lash measurements and adjustments must be made with the engine stopped, and with the valves FULLY CLOSED.

If the measurement is not within this range adjustment is necessary.

NOTE: For valve lash specifications and measurement procedure refer to Fuel System; Crankshaft Positions For Valve Lash Setting, located in this manual.

Finding Top Center Position for No. 1 Piston

Table 1

Tools Needed
Part Number	Part Name	Quantity
8T-0292	Bolt	1

Note: The hole (2) can be in one of two positions:

 

• The right front face of the flywheel housing (Illustration 2)
• The left front face of the flywheel housing (Illustration 3)

 

1. Remove the plug (4) from timing hole (2) from the front side of the flywheel housing (3) .Note: Turn the engine with the four large bolts on the front of the crankshaft. Do not use the eight small bolts on the front of the crankshaft pulley.

 

2. Put top center bolt (1) through timing hole (2) in the flywheel housing (3) .Turn the flywheel in the direction of normal engine rotation. Turn the flywheel until the timing bolt engages with the hole in the flywheel.Note: If the flywheel is turned beyond the point of engagement, the flywheel must be turned in the direction that is opposite of normal engine rotation. Turn the flywheel by approximately 30 degrees. Then turn the flywheel in the direction of normal engine rotation until the timing bolt engages with the threaded hole. When the No. 1 piston is at the top center position, this procedure will remove the play from the gears.

 

3. Remove the valve cover.The inlet valves and the exhaust valve for the No. 1 cylinder are fully closed under two conditions:
   • No. 1 piston is on the compression stroke.
   • The rocker arms can be moved by hand.

   If the rocker arms cannot be moved and the valves are slightly open, the No. 1 piston is on the exhaust stroke.

   Note: Refer to Testing And Adjusting, “Engine Valve Lash -Inspect/Adjust”.

 

4. After the timing bolt has been installed in the flywheel, complete these procedures, as required:
   1. Find the cylinders that need to be checked for the stroke position of the crankshaft.

    

   2. Find the cylinders that need to be adjusted for the stroke position of the crankshaft.

 

5. When the actual stroke position is identified and the other stroke position is needed, remove the timing bolt from the flywheel.

 

6. Turn the flywheel by 360 degrees in the direction of normal engine rotation.

Note: The timing hole is used during the procedure to set the valve lash.

Valve Lash and Valve Bridge Adjustment

Table 2

Valve Lash
Valves	Dimension of Gauge
Inlet	0.38 ± 0.08 mm (0.015 ± 0.003 inch)
Exhaust	0.64 ± 0.08 mm (0.025 ± 0.003 inch)

Adjust the valve lash while the engine is stopped.

 

1. 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”.
   

   Table 3

   TC Compression Stroke	Inlet Valves	Exhaust Valves
   Valve lash	0.38 ± 0.08 mm (0.015 ± 0.003 inch)	0.64 ± 0.08 mm (0.025 ± 0.003 inch)
   Cylinders	1-2-4	1-3-5

 

2. Adjust the valve lash according to Table 3.
   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.

    

   2. Loosen the adjustment locknut.

    

   3. Place the appropriate feeler gauge between rocker arm and the 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.

    

   4. Tighten the adjustment locknut 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.

 

3. 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.
   

   Table 4

   TC Exhaust Stroke (3)	Inlet Valves	Exhaust Valves
   Valve lash	0.38 ± 0.08 mm (0.015 ± 0.003 inch)	0.64 ± 0.08 mm (0.025 ± 0.003 inch)
   Cylinders	3-5-6	2-4-6

   ( 3 )

   Position for No. 1 cylinder

 

4. Adjust the valve lash according to Table 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.

    

   2. Loosen the adjustment locknut.

    

   3. Place the appropriate feeler gauge between rocker arm and the 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.

    

   4. Tighten the adjustment locknut 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.

 

5. Remove the timing bolt from the flywheel after all adjustments to the valve lash have been made. Reinstall the timing cover.

If you need visual instruction to adjust the valves, you can watch this video.