These bucket tappets were usually adjusted by a small shim, either above or below the tappet.
A much improved system placed the shims "above" the tappet.
In the 1990s the rear main seal was changed from a two-piece component to a one-piece design and provisions for roller tappets were also added.
It is also affected by the adjustment of the valve mechanism, and particularly by the tappet clearance.
But a cam sometimes touches the tappet, and metal bearing surface wears with insufficient oil or with too much / too little clearance.
The design uses hydraulic tappets and incorporates the provisions for a hydraulically controlled propeller installation as well.
Flat tappet engines and cartridge bearing need zinc.
The tappet clearances are maintained by the flow of the engine's lubricating oil.
