Hydraulic lash adjuster
Keeps valve clearance at zero automatically.
Under the pivot end of each finger follower.
Engine oil fills a small plunger chamber, taking up slack so the valvetrain stays quiet without manual adjustment.
A self-adjusting doorstop that always fits the gap.
A ticking noise after a cold start can come from adjusters that have drained, though it should clear quickly.
Usually condition-based rather than a routine replacement. Lubrication, overheating and the exact engine affect wear.
Internal-engine work is usually labor-intensive. Diagnosis and the engine code determine the repair scope.
Classic BMW M engines such as the S14 used solid lifters set by hand; most later BMW engines use hydraulic adjusters.
BMW petrol and diesel engines; petrol-only systems are identified individually.