Ah Pobjoy
Indeed the Pojoy is a light and powerful unit,but aside from the mag situation the valves are a 'weak spot' and need to be changed to a modern material.
The R had exposed valve gear supposidly lubricated by grease (not very well) and the main advantage of the Niagra and Cateract was the oil fed enclosed system.
This system relied on small pipes giving a metered oil supply to the rocker covers (top cylinders),but this can 'silt up' and it is best to actually inject oil into the rocker on a regular basis to ensure some lubrication takes place.
Aside from that i have never had a mechanical failure of the engine or gearbox in hundreds of operating hours.
Used to have 'issues' before changing the valves,but one has to accept that with the territory.
The unit had a fairly low overhaul life because of this,and would have seen valves replaced on a regular basis when they were readily available.
All in all this is a great engine to fly behind and gives great thrust for little weight.