Forum

[Bandit12]

Hi, I've just finished restoring a 1959 big head bullet. I would attach a photo but I'm unsure how. What I'm also unsure about is how to do a 12 volt conversion. I've heard that the 6volt stator does not need changing but that 2 of the 3 wires are joined. Is this correct?

Also despite numerous attempts with new rubber seals and instant gasket the chaincase still drips oil when the engine is running but stops the moment the engine is switched off. It appears to be coming from underneath, level with the left footpeg. The mating surfaces are clean with no obvious damage or warping.

Any advice is gratefully appreciated

Bandit

[Nettshubby]

With the older Lucas stators, you used to join the light and dark green wires, then, if memory serves, connect this joined pair amd the third one to a rectifier, then to a diode to drain off excess current as heat through a finned heat sink. I'm not a hundred percent sure whether the diode is connected first, or the rectifier. No doubt a better memory than mine will fill in the details!

[Adrian]

Bandit12

,

you can sign up for a picture hosting web site eg www.imageupload.co.uk - it's free. I would avoid sites like Photobucket and Tinypics, though - Once you have set up your account and uploaded your photos there, it will give you a number of different codes you can use for publishing your pictures on different web sites and forums.



So with your Big Head Bullet pics safely uploaded, choose the one(s) you want us to see, and copy and paste the HTML code into your message here. I repeat, PASTE THE ***HTML CODE*** here. Do ***NOT***, repeat, do ***NOT*** paste the BBCode for forums, even though this is a forum, because only HTML works here.



I have converted a 1957 500 Bullet to 12V (similar to yours apart from the cylinder head casting), fortunately the original alternator on mine was still healthy enough to do the job. If in doubt replace the alternator for a Lucas RM21 or its Sparx equivalent. You could go for the three-phase alternator but a good single phase item will crank out all the juice your Bullet's electrics will ever need. Converting to 12V will allow you to simplify the wiring too, especially if your Bullet still has SR1 magneto ignition as the earliest Big Head Bullets did.



Under Nettshubby's scheme the rectifier was connected first, light and dark green wires joined to one AC terminal, third wire to the other AC terminal as he says, with the zener diode linked to the DC feed into the charging circuit. However you can forget about separate zener diodes and rectifiers, keep it simple and get yourself a combined 12V regulator/rectifier, ideally with a built in capacitor, so that you can run the bike battery-less if you need to. Our hosts sell the Boyer Brandsen power box, though the Sparx SPX023 version from Andy Gregory is at least £20 cheaper. Whichever you use, don't tuck it away in the tool/battery/air cleaner box, mount it externally for air cooling.



A.

[Nettshubby]

Ah yes, zener diode! Forgot that name. I once converted a Ducati 350 Sebring to 12 v, but bought a diode from
Maplins or RS. Fixed it to an alloy plate about 3 inch square as a heat sink. It blew in
the IOM and I had to run with the headlight on all the time. It wasn't a large output
alternator so it balanced ok like that.

[Bullet Whisperer]

Nettshubby, it is the dark green and mid green [green and black and green and yellow which you should join together, the light green, or green and white stays on its' own, this gives maximum output. If using a 'Powerbox' or similar, these 'two' wires from the alternator can go either way round into each of the yellow wires and 12V DC will come out of the black and red wires, to earth either way round and feed whatever lights etc you may or may not have. Regards, Paul.

[Bullet Whisperer]

Just to add, the oil is probably being blown out from the mainshaft hole in the back of the chaincase, due to the virtually useless cork crank seal on the drive side of the engine allowing crankcase pressure to get in the chaincase and escape via the aforementioned hole. I fit proper seals to the drive sides of these engines, to fix this and other breathing and messy oil related problems.

[PeteF]

Second the Whisperer, the leak will be at the mainshaft if it only drips when running. Power box is the way to go with the electrics; I did this to a 6v Triumph with great results.

[simon]

Ive always kept my 6v bikes original. A well set up 6v system works fine and with new led bulbs available that work on a range of voltages there is really no advantage imho.

[Revband]

I would agree with you Simon on a bike which has a dynamo, the voltage regulation on a 6v alternator is so crude that changing it to 12v has a lot of advantages.

[Dennis C]

As revband says, also using led bulbs in a 6v alternator system will totally bu##er up the already crude charge regulation. The result will be a knackered battery in a very short time.