Camshaft lobe wear on pre-1989 engines
M103Engines built before 1989A tapping or ticking from the top of the engine, and metal in the oil.
A known weakness of the early build only. The timing chain itself is robust on this engine, but the plastic chain guides go brittle with age — if the head is off for any reason, they are replaced while it is accessible rather than as a second job later.
Parts this needs
Checked against en.wikipedia.org

