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LO 9-10 Outline the service procedure used to adjust the clearances of intake and exhaust valves

Site: CDX Learning Systems
Course: DE Section 2-1: Engine Blocks and Cylinder Heads
Book: LO 9-10 Outline the service procedure used to adjust the clearances of intake and exhaust valves
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Date: Thursday, 5 November 2026, 7:44 PM

Table of contents

1. Performing a Valve Adjustment

LO 9-10: Outline the service procedure used to adjust the clearances of intake and exhaust valves.

 

Performing a Valve Adjustment

As valve seats, faces, and the tip of a valve stem wear, the clearances between the valve stem and the rocker lever change. The camshaft and other valve train parts can wear as well, which changes the timing of valve opening and closing. As this happens, the engine’s ability to move air in and exhaust gases out is altered. The duration of each stroke changes and engine operation deteriorates, with power output dropping, engine brakes not working as effectively, and fuel consumption and emissions increasing. Today’s engines use valve angles and valve train materials that are extremely wear resistant, which means the need to adjust the valves is less frequent than just a few years ago. In fact, adjusting valve lash is a procedure done less frequently than simply checking the valve lash. Today’s valve bridges are universally nonadjustable, and few engines in service use adjustable bridges or crossheads.

To perform a valve adjustment for an in-line six-cylinder engine with a firing sequence of 1-5-3-6-2-4, follow the steps in Skill Drill 9-2. This generic procedure uses the concept of identifying paired cylinders to determine which valves can be adjusted. This procedure is outlined with the assumption that there is no engine compression release brake on the engine.

 

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1.1. SKILL DRILL 9-2  Performing a Valve Adjustment

SKILL DRILL 9-2  Performing a Valve Adjustment

 

STEP 1
Clean the upper engine with a pressure washer.

STEP 2
Locate original equipment manufacturer (OEM) service literature for the actual valve adjustment procedures.

STEP 3
Unless the manufacturer indicates that their valve adjustment specifications are for warmed engines, lash should be adjusted on a cold engine. If the OEM indicates that a warm engine is required, bring the engine operating temperature to 140° F (60° C).

STEP 4
Remove the valve cover or rocker housing cover(s). Position the engine at TDC unless otherwise indicated. Use the companion cylinder method to find TDC for the end-of-compression stroke for cylinder 1. This is done by positioning the engine at TDC. Cylinder 6, the companion of cylinder 1, should have two tight rocker levers because the valves should both be open as the engine moves through overlap position. If not, rotate the engine 360 degrees and recheck. Cylinder 1 should have both valves closed because it is finishing the compression stroke and beginning the exhaust stroke. At TDC position, half of the valves can be adjusted. Use the provided table to find the adjustable valves.

STEP 5
With the engine at cylinder 1 TDC (end-of-compression stroke), check the valve clearance by inserting the correct thickness gauge between the rocker lever and the valve stem or bridge. The blade should slide between the two machined surfaces easily, but a light amount of drag should be felt when pulling and removing the blade. If the setting is correct, mark the rocker with a yellow crayon marker. Follow this sequence for all valves that can be adjusted at cylinder 1 TDC.

STEP 6
Rotate the engine 360 degrees in the correct direction of rotation until cylinder 6 is at TDC (end-of-compression stroke). Cylinder 1 should be on overlap, and both rocker levers should be tight because the valves are both open. Both rocker levers should be loose on cylinder 6.

STEP 7
Repeat the procedure for checking the adjustment for the remaining intake and exhaust valves.

STEP 8
If the lash is too loose or too tight, it needs to be adjusted to the correct clearance. To adjust valve lash, loosen and back off the locknut on the rocker adjusting screw. Initially back off the adjusting screw for the rocker lever as well.

 

STEP 9
Screw down the adjusting screw until the rocker lever clearance just disappears. Next, back off the adjusting screw sufficiently to insert the correct-size thickness gauge.

STEP 10
Turn the adjusting screw down again until a moderate amount of resistance is felt after the screw makes contact with the thickness gauge. This step overtightens the screw and reduces the amount of valve clearance.

STEP 11
Check the thickness gauge drag. If the drag is acceptable, snug up the locknut while holding the screwdriver to prevent rotation of the adjusting screw and to maintain correct lash clearance. Tightening the locknut will pull on the threads of the adjusting screw and increase clearances slightly. After tightening the locknut, the correct valve lash clearance should be established.

STEP 12
Torque the locknut to the correct OEM specifications.

STEP 13
Reinstall rocker housing cover(s) following the manufacturer’s procedure. Most current on-highway diesel engines use rocker housing cover gaskets that are reusable, provided that they are installed clean and torqued correctly.

 

  Adjustable Valves  
Cylinder 1 2 3 4 5 6
  
Valves E I E I E I E I E I E I
Cylinder 1 TDC X X O X X O O X X O O O
Cylinder 6 TDC O O X O O X X O O X X X

 

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