Setting Valve Lash (One-Pager)

Setting Valve Lash
1989–Current Cummins Flat Tappet Engines

Applies to 12-valve, early 24-valve, and common rail flat tappet setups.

Not for hydraulic roller lifter engines.

Tools Needed
0.010-inch feeler gauge for intake
0.020-inch feeler gauge for exhaust
9/16-inch or 14 mm wrench
11 mm wrench for some aftermarket adjusters
A method to rotate the engine by hand
Lash Specifications
Intake

0.010 inch

Exhaust

0.020 inch

Set lash with light drag on the feeler gauge—not too tight and not too loose.

Step 1 — Find TDC Compression

Rotate the engine in its normal right-hand direction.

Watch cylinder number 6. As the exhaust valve comes up and the intake valve just begins to crack open, cylinder number 6 is on valve overlap and cylinder number 1 is at top dead center on the compression stroke.

Step 2 — Set the First Group

When cylinder number 6 is on overlap, adjust:

Cylinder Valve
Cylinder 1 Intake and exhaust
Cylinder 2 Intake
Cylinder 3 Exhaust
Cylinder 4 Intake
Cylinder 5 Exhaust

Intake: 0.010 inch
Exhaust: 0.020 inch

Step 3 — Rotate the Engine Again

Continue rotating the engine in the normal right-hand direction and watch cylinder number 1.

When the exhaust valve comes up and the intake valve just begins to crack open, cylinder number 1 is on valve overlap and cylinder number 6 is at top dead center on the compression stroke.

Step 4 — Set the Second Group

When cylinder number 1 is on overlap, adjust:

Cylinder Valve
Cylinder 6 Intake and exhaust
Cylinder 5 Intake
Cylinder 4 Exhaust
Cylinder 3 Intake
Cylinder 2 Exhaust

Leave cylinder number 1 alone during this step.

Final Check

Confirm that:

All intake valves are set to 0.010 inch.
All exhaust valves are set to 0.020 inch.
The feeler gauge has light drag.
All locknuts are tightened.
The valve-train area is clear before reassembly.
Important

If your engine still uses factory hydraulic roller lifters, do not set valve lash.