Also known as a rocker arm eccentric, used to adjust valve lash

This eccentric sits inside the rocker arm and is used to adjust the valve lash. Older BMW engines that use solid lifters should be adjusted for their valve clearance to ensure proper performance and power. Over time, these eccentrics can wear out resulting in their replacement. A sign that the eccentrics are worn is if you cannot properly set the valve lash.

Technical note: Unlike modern engines with hydraulic lifters, older BMW engines use mechanical lifters which have an inherently noisier operation. "Ticking" is okay and perfectly normal when these engines are running. Less ticking means your valves are out of adjustment and the engine is probably running rough. Too much ticking is another sign that the valve lash is too tight.

M30 and M20 engines have 12 rocker arms and therefor use 12 adjusting eccentrics, M10 engines have 8 rocker arms and therefor have 8 adjusting eccentrics. When setting the valve lash the engine must be completely cold. FCP Euro recommends valve adjustments on M10, M20, and M30 engines every 12,000-15,000 miles.

Adjustment range:
M10 4 cylinder -.15mm (.006") when cold or .20mm (.008") when warm
M20 6 cylinder - .25mm (.010") when cold or .30mm (.012") when warm
M30 6 cylinder - .30mm (.012") when cold or .36mm (.014") when warm