Valve Adjustment
Also called tappet setting
Valve clearance is the small gap that lets valves close fully when hot. Too large and the engine ticks and loses efficiency; too small and valves stay slightly open, burning the valve face and costing compression. Clearances close up with wear, and faster on CNG, which runs hotter and drier. Adjustment restores the specified gap on engines with adjustable clearances. It will not fix a burnt valve, a worn camshaft or a leaking head gasket, which need the head removed.
Signs you need this
- Ticking or tapping from the top of the engine at idle
- Hard starting and weak low speed pulling power
- The car runs on CNG and has covered high mileage since the last adjustment
- Uneven compression readings across cylinders
- A previous adjustment was done without measuring, or long ago
Not all of these have to be present, and one of them on its own can mean something else entirely. That is what the diagnosis is for.
What the job includes
- Engine set to the correct temperature and position for measurement
- Every valve clearance measured and the before figures written down
- Adjustment by screw or shim to the maker's specification
- Camshaft lobes and rocker faces inspected for wear while open
- New rocker cover gasket and correct torque on refitting
- Running check and road test, with after figures recorded
How we do it
Set the conditions
Clearances are only meaningful at the temperature and crankshaft position the maker specifies, so we set both first.
Measure and record
Each valve is measured with feeler gauges and the reading is written down before anything is touched.
Inspect the top end
Camshaft lobes, rockers and shims are checked for wear, since a worn lobe cannot be corrected by adjustment.
Adjust to specification
Clearances are set by screw or by changing shims, then rechecked after locking, because settings move as they lock.
Reassemble and test
A new cover gasket is fitted, the engine is run and listened to, and a road test confirms starting and pulling improved.
How we work
The same on every job, which is why we can write it down.
Diagnosis before quote
We find the fault first. A price given over the phone for a noise nobody has heard is a guess.
The price is agreed first
You approve the work and the cost before a spanner is picked up. Extra work means another call.
Parts you can check
We tell you whether a part is genuine, OEM, aftermarket or used, and what each one costs.
Old parts returned
Ask and we will hand back whatever we replaced. It is the simplest proof that the job was done.
Book valve adjustment
Fill this in and a person will call you back to confirm the time and the price. Only your name and one way to reach you are required.
You send this
Takes a minute. No payment, no obligation.
We call you
To confirm the car, the time and the location.
Tell us the car and the symptom
We will arrange a mechanic at your location, or a slot at the nearest workshop. No payment until the price is agreed.