I'm sure that I've seen a reference to operating the 6v starter motor on 12 volts.
I have just rebuilt the engine in my 6v RN so it is a little stiff and the starter motor struggles a bit (as do I!)
Is it possible to apply the 12 volts to just the starter motor in order to spin the engine over whilst I'm fiddling with the ignition and carb settings? Is it safe to put 12v through the starter button?

Location: Near M1 Jtn 28

In short YES,I converted to twelve volt running several years ago with no problems to the motor or contacts.The six volt wiper even copes with the extra volts although the water is thrown from the screen rather than wiped as the blades wip from left to right. Are you going to run a separate feed for the starter? if not don't turn on the lights or the bulbs will blow.The coil should cope if not running for extended period,or to be on the safe side use a 12v version jury rigged into the system.

Location: Piddle valley, Dorchester.

Many thanks Peter, I want to keep the car on 6v for normal use but it would be useful to use 12v just for the initial setting up. I was thinking of using a spare 12v battery with jump leads attached to the connection on the input side of the switch and the mounting flange on the motor so that 12v doesn't go anywhere else. Mine is a negative earthed car so I just need to make sure that I'm connecting the leads the right way round.
The 6v battery will still be providing power to the coil etc.

Location: Near M1 Jtn 28

Brian, it is generally accepted that in normal use the 6v starter will be fine with 12v, but take care if the engine is tight. At a slow cranking speed the current is higher, so if with 12v it only spins slowly then you could possibly damage the starter motor if you spin it for long. Short bursts with time to cool between might be best.

I think that it would be adviseable to disconnect the 6v feed from the starter entirely, making sure that there is 6v only, feed to the coil etc before trying to connect in the 12v.

Location: Oakley ,Hants

Many thanks Andrew & Derek, that all sounds like good advice.

Location: Near M1 Jtn 28