Valve lash is one of those maintenance items that gas-engine owners never think about and that a lot of Cummins owners don't realize applies to them either. The 6.7 Cummins, like the 5.9 before it, uses a solid valvetrain, which means there is a small mechanical clearance in the valve mechanism that has to be checked and occasionally adjusted. Ignore it long enough and you can lose performance or, in the worst case, damage valves. This guide explains 6.7 Cummins valve lash adjustment in plain terms: what it is, why it matters, what the symptoms of a problem look like, and how the job is done.
Exact clearance specifications and the inspection interval live in your service manual for your specific engine year. Those numbers are precise and must come from the manual, not from a blog. This guide is about understanding the job so you know when it matters and what a shop is doing when they quote it.
What valve lash actually is
The valvetrain opens and closes the intake and exhaust valves through a chain of parts: the camshaft, pushrods, and rocker arms. Because these parts expand as they heat up, the system is built with a tiny deliberate gap, the valve lash or valve clearance, so the valves fully close when everything is at temperature. Unlike many gas engines that use hydraulic lifters to take up that gap automatically, the Cummins uses a solid mechanical setup, so the clearance is set by an adjusting screw and a locknut on each rocker and must be checked by hand.
The intake and exhaust valves use different clearance specifications, and the adjustment is made with the engine cold so the readings are consistent and repeatable. That's the whole idea: a set, correct gap that keeps the valves sealing properly across the temperature range.
Why it matters
Valve lash drifts over time as the valvetrain wears and the valves seat deeper into the head. Left unchecked, it usually drifts toward tighter clearance, and that's the dangerous direction.
- Too tight and a valve can be held slightly open as the engine heats and the parts expand. A valve that doesn't fully close loses its ability to shed heat into the head through the seat, and it can burn. A burned valve means a compression loss, a misfire, and a head job.
- Too loose and the valvetrain runs noisy, the valve opens late and closes early, and you lose a little performance and put extra impact wear on the components. It's the less catastrophic direction but still not correct.
Correct lash keeps the valves sealing, cooling properly, and operating on the timing the engine was designed around. It's a long-interval check, not a frequent one, but it's a real one.
Symptoms of valve lash out of spec
Because it's a slow drift, valve lash problems creep up rather than announcing themselves:
- A ticking or tapping from the valvetrain that grows over time often points to loose clearance.
- A developing misfire, rough idle, or power loss can indicate a valve being held open by clearance that's gone too tight and a seat that's no longer sealing.
- Higher-than-normal wear or noise after very high mileage without a lash check.
Most owners never hear a dramatic symptom, which is exactly why the manufacturer schedules a periodic inspection rather than waiting for one. The check is cheap insurance against the expensive failure.
How the adjustment is done
The job itself is methodical. With the engine cold and the valve cover off, the technician rotates the engine to bring each cylinder to the correct position on its firing order so the valves being measured are fully closed. A feeler gauge of the specified thickness is slid between the rocker and the valve to read the clearance; if it's out of spec, the locknut is loosened, the adjusting screw is turned to set the correct gap, and the locknut is torqued back down while holding the setting. This repeats for every intake and exhaust valve in sequence. When it's done, the valve cover goes back on with a fresh gasket, which is why a valve cover gasket is part of the parts list for this job.
It's not a difficult job for a competent DIYer with a service manual and patience, but it demands the correct specs and careful, repeatable technique. Getting a clearance wrong in the tight direction is worse than not touching it at all, so if you're not confident, this is a fair thing to hand to a diesel shop.
Parts you'll need
The adjustment itself uses no consumable parts beyond a fresh valve cover gasket, and you'll want the correct feeler gauges and a torque wrench for the locknuts. Since you're already under the valve cover, it's a sensible time to address any weeping gaskets or seals in the area. Everything here is organized by engine so you can find the right 6.7 Cummins gaskets and seals for your truck and confirm fitment for your application.
FAQ
Does the 6.7 Cummins really need valve lash adjustment? Yes. It uses a solid valvetrain, so valve clearance is a periodic inspection-and-adjust item on the long-interval side of the maintenance schedule. Your service manual gives the interval and the exact specs.
What happens if I never check valve lash? Clearance tends to drift tighter as the valves seat in, and a too-tight valve can be held open, lose its ability to cool, and burn, leading to a compression loss and a head repair. The periodic check prevents that.
Can I do valve lash myself? A competent DIYer with the service manual, correct feeler gauges, and a torque wrench can do it, following the firing order and setting each valve cold. If you're not confident, hand it to a diesel shop, because a wrong setting in the tight direction does real harm.
Where we land
Valve lash is a quiet, long-interval maintenance item that a lot of 6.7 Cummins owners don't know applies to them until a shop mentions it. The engine's solid valvetrain needs the clearance checked periodically to keep the valves sealing and cooling. Follow your manual's interval and specs, address it with correct technique, and it's cheap insurance against a burned valve and a head job down the road.
Shop 6.7L Cummins diesel parts at coredieselparts.com. Free shipping over $70, ships fast. Browse gaskets and seals organized by engine, and confirm fitment for your application.
Related guides: - Diesel Maintenance Schedule by Mileage - 6.7 Cummins Maintenance Schedule and Service Intervals