On the transverse M260 and longitudinal M264 four cylinder petrol engines the valve seat or the valve guide wears early. The symptom: check engine light, rough running, misfire on one or more cylinders. Sometimes without any fault code being stored.
Show the restHide
According to the maker's official service bulletin (LI01.30-P-072328) the valve seat leaks. After the leak test, if a leak is found at the valves, the whole cylinder head has to be replaced: the valve seat cannot be refurbished. The roller width of the intake and exhaust side followers differs, and swapping them is prohibited.
In the United States the maker announced a 15 year / 150,000 mile (about 240,000 km) extended emissions warranty for the M260 group (MY2019 to 2022 A / CLA / GLA / GLB). Outside the United States that programme does not apply automatically, but the fault is the same mechanism. The GLB 250, the CLA 250 and the A 220 use this engine.
What to check
- Ask for a fault code read: misfire codes of the P0300 / P030x kind and mixture formation codes are suspect
- On a cold start watch for rough running and the check engine light
- Ask whether the cylinder head has already been replaced: according to the service bulletin that is the repair, not valve lapping
