When I moved from P & W to sleeve valves ( I did the course at Bristol) like Flying Pram I thought this will never work and if it did not for long
and the bellcrank mentioned looked like is was only strong enough for a lawn mower
I worked Hercules and Centaurus and they beat the P & W into a cocked hat
P&W 1830 had a an ARB TBO life of 1400 hours but the Centaurus we ran 2,200 hours
No routine maintenance on the sleeve part of the engine,and nothing to set up or adjust in service
P&W valve clearance adjustment and rocker check every 500 hours.
Rocker check took 3 guys 2-3 hours !
Changed 50 plus cylinders on P&W all failures ( Some spectacular
.)
Changed 2 on the Centaurus one for a stripped plug thread
Never heard of a sleeve failure
Centaurus had LT ignition much easier than Magnetos on 1830