Valve Clearance (S50B30, 3.0L M3 Only)
Symptoms
Hard starting, reduced power, and eventually exhaust valve recession (the valve sinks into the seat and doesn't seal properly). May also cause a tapping noise from the head.
Cause
The S50B30 uses shim-under-bucket valve adjustment (no hydraulic lash adjusters). Valve clearances tighten as the valve seats wear. Tight exhaust valve clearances prevent the valve from fully closing, which causes overheating of the valve face and accelerated seat recession.
Fix
Check and adjust valve clearances every 50,000 km.
The job requires removing the camshafts to access the shim buckets, not a quick task (6-8 hours).
Cost: $400-800 at a specialist.
The later S50B32 (3.2L) uses hydraulic lash adjusters and does not require manual adjustment.
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