On factory M10/M30 cylinder heads, the rockers are held in position by a spring – and at high rpm, that spring may allow the rocker to move in relation to the valve stem (sometimes enough to walk off the valve stem which quickly results in a broken rocker arm). With rocker arm locks, you eliminate the spring and positively locate the rocker arm. Locks also make head assembly simpler than with thrust springs. We use these on all our performance engines.
Installation Note: These locks are meant to replace the existing retention springs, use in conjunction with the OEM shim washer. When installing; use a feeler gauge to space the lock .011″-.015″ from the rocker. This will allow for natural heat expansion of the rocker and lock while under normal use.
SPECIAL NOTE FOR M30’s: There is one rocker lock near the thermostat housing that needs to be trimmed to fit past the water jacket inside the cylinder head (see photo).
M10 4cyl. engine: order 8 for complete set.
M30 6cyl. engine: order 12 for complete set.