The risk of to hot a plug is detonation, leading to major engine damage. Found this quote from John Healey of TIOC, guy probably knows as much about old British engines as anyone on the planet. The original post was about going to a hotter plug to stop oil fouling Note the comments on oil in the combustion chamber changing the gas/air ratio and the comment on going to a hotter than recommended plug to stop the oil fouling. It's your bike but if it was mine I would trust what Jim C and John H say and run the recommended plug. They have both earned their pipe and slippers many times over with decades of practical experience.-I put the N4Gs in today. Only some short runs with the BP6ES plugs, so risk was minimal.
"Toughening a motor to detonation is more than raising the octane of the fuel you put in the tank. Especially since it is not always possible. You mentioned compression and the lower the compression the less the incoming charged is compressed the less the engine will be prone to detonation. Compressing the fuel/air mixture raises it temperature.-So the guys running 87 are more at risk than those of us running 93.
And controlling detonation is all about controlling heat:
- If the ambient air temperature increases the engine will be more prone to detonation.- It does get hot here in August
- If the rings haven't seated, and thus have the ability to transfer heat out of the piston, the engine will be more prone to detonation.-They have
- If you were talked into using modern thin rings that do not transfer enough heat your engine will be more prone to detonation.-I wasn't
- If the rings haven't seated and oil is getting in the combustion chamber you are lowering the octane of the incoming fuel/air your engine will be more prone to detonation.
- If you have a valve job where you were talked into a "performance" valve job with valve seats widths of .040" or less your engine will be more prone to detonation.-Didn't happen
- If you are convinced that Triumph didn't know what they were doing when they determined the overall gearing in high gear and the engine rpm when doing highway speeds your engine will be more prone to detonation.-I was Triumph spec I quoted with the BP6ES
- If you are convinced that Triumph didn't know what they were doing when they suggest a spark plug your engine will be more prone to detonation.-See above
- If you are selecting the grade of plug for fuel or oil fouling, instead of temperature your engine will be more prone to detonation.
- If you haven't removed all of the sharp edges on the piston and combustion chamber your engine will be more prone to detonation.-This engine was rebuilt years ago, hasn't been opened since.-
If the valve margins are too thin, they will not cool properly your engine will be more prone to detonation.-Rebuilt with stock valves
- If you do anything to hinder the transfer of heat out of the cylinder and head fins your engine will be more prone to detonation.-Such as?
- In places where the ambient air temperature exceeds 100° F being careful of riding style and monitoring oil temperature is something I would consider.
The ability to control heat is the limiting factor in what you can expect from one of these engines."-The new pipes aren't bluing, so....