Not m/c but I bet this is answered here.

[electrajohnt]

My cousin has a late forties Petrol Morris Commercial truck. The coil gets hot it runs ok but the coil gets hot. Change the coil, that gets hot. Electrics otherwise seem to work ok.
Has anyone got an idea what could be the problem. Your help would be appreciated.
JohnAT

[alanjennings]

My friends royal Enfield coil also runs hot! No problem, but coils

are best not boxed in to let the generated heat escape.

[SPRIDDLER]

No idea if this applies but I had an old Bedford van. It was a 12v system but was designed to have (and had) a 6v coil fitted to assist starting.
When starting the full battery 12v was delivered to the 6v coil but once the engine was running and the starter was disengaged the voltage to the same 6v coil was diverted through a ballast resistor which cut the voltage to 6v.
Maybe worth a look at a wiring diagram to see if a ballast resistor is shown in the feed to the coil. If so, perhaps the resistor is faulty or the switch isn't bringing in the ballast resistor.

Maybe it's normal for your pal's coil to run hot.

[Tolly]

Coils do heat up, that's why they are oil filled. If the outer casing has been damaged and the oil leaked out they can break down due to over heating. Not saying that has happened to this coil but just to state they can run hot.

[Dibnah]

A coil with reversed polarity connections can overheat.