Valve Adjustments Explained

By Allstate Peterbilt Group | Posted in Certified Pre-Owned, Cummins Engines, Mobile Service, PACCAR Engines, Service and Parts on Friday, December 15th, 2017 at 5:06 pm
Service Valve Adjustment

Why You Need a Valve Adjustment for Your Diesel Engine

A valve adjustment (sometimes also called an overhead) is vital to the health of your diesel engine to ensure proper combustion. This is often an overlooked task for proper engine maintenance; however, neglecting your valves could lead to a lot of unwanted hassles like loss of power and decreased fuel efficiency. Keeping a close eye on the valve lash can alert you to a problem before it leads to hefty repair costs for your diesel engine and a lot of unplanned downtime.

What is a valve adjustment?

The valve mechanism (push rod, lifter, and rocker arm assembly) is adjusted so that the lash has the proper clearance necessary to regulate the opening and closing of the valve. If the lash clearance is too great, it will affect the engine’s airflow and will eventually lead to valve damage. If the lash clearance is too tight, the valve cannot close and seal properly in the cylinder head, and exhaust gases will leak past the valve. The valve lash is also the only way for the valves to pass heat into the cylinder head.

When do I need to have a valve adjustment?

You should have your valve lash inspected at manufacturers recommended intervals. A sure sign that it’s time for a valve lash adjustment is if your engine is making a loud clicking or tapping noise when starting up or if you experience a loss in engine power. You can find more details on the suggested adjustment frequency here.

Why is a valve adjustment procedure important?

If you neglect to do a diesel engine valve adjustment for an extended period of time, a catastrophic failure of the valve and engine is likely to occur. A number of problems could occur that will hinder your truck’s performance and potentially leave you with more repairs to address. These issues include:

  • The engine will not operate at full power
  • You will burn through fuel quicker
  • You will have increased exhaust smoke

Should I attempt a diesel engine valve adjustment myself?

While some people do their own valve adjustments, there is a lot that can potentially go wrong. A valve that is not adjusted to the proper clearance could end up with exhaust gases leaking past the valve or worse engine performance. Either of those scenarios could end up costing you more money than getting your engine serviced by professionals.


If you are in need of a value adjustment procedure, visit Allstate Peterbilt’s service department. We also offer body shop services around the Midwest and a mobile truck service for convenient truck maintenance on the road.

8 Responses to “Valve Adjustments Explained”

  1. Gregar says:

    Very nice content and I like this very much.

  2. Miron says:

    I need to 2came vale adjusting Diesel eingne

  3. Caden Dahl says:

    If I had a truck like this, I would for sure want to do all of the maintenance on it. As you said, getting a valve adjustment would be a good thing to do. I would see about having a shop do it for me as I don’t have a way to do it myself.

  4. This article helps all the truck owner, they will have a great idea to improve their diesel truck engine performance. They can also do the deletion of DPF DEF EGR VGT on Volvo, Detroit, and Cummins trucks which will enhance their truck even more!

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