1. Wire bike for 12 volts, see 6 to 12 volt conversion page
2. Parts You Need
You need to accumulate these parts:
Larger 12 volt battery to mount in box (standard riding lawnmower battery will work)
Auto advance timer for 45 with a 15 degree advance (Sportster timers fit but have 30 degrees advance)
1964-65 is cheapest and worst; I would advise not to buy one of these, they are extremely hard to adjust
1966-73 is most expensive, hardest to find, and best, this is what you need to buy
Alternative is to have advance changed to 15 degrees on a Sportster timer
1964-65 Harley electric starter top and starter gear box (cheapest and works) or 1966-73 electric starter top with gear box and solenoid (most expensive, hardest to find, and works best).
Six 10-24 x 7/16 cstk screws #1762W, available from after market suppliers
Two 10-24 x 1 ctsk screws #1781W, available from after market suppliers
1964-73 electric starter clutch basket with starter gear ring
Harley electric starter motor 31455-64A
Electric starter relay 71455-67 or similar relay
3. How to Do It
Remove smaller original battery from frame mount under seat and Install larger 12 volt battery (possibly riding lawn mower battery) in servicar box and wire.
Install auto advance timer.
Remove transmission case top, outer primary cover, and clutch assembly.
Install electric starter clutch basket with ring gear and reassembly clutch
Drill and tap holes at top of transmission case, which hold top to case, to accept 10-24 threads. I believe this is a special weird Harley size thread, however many aftermarket suppliers sell this tap. I personally would be scared to do this with transmission together and in frame, however it might can be done with care. Not sure. Transmission gears will eat up any left over metal fragments.
Install electric starter top and gasket with the 8 larger 10/24 cstk screws, if using 1964-65 assembly you will have to also bolt the starter gear box to the top.
Partially install the primary cover to mark the area at the top which will need to be cut out were starter gear meshes to ring gear on electric starter clutch basket.
Cut only needed area out and reinstall the primary cover
Install starter motor to top.
Mount the starter relay, servicars typically had them mounted under the box or next to battery.
Run positive line to starter's positive terminal with relay installed inline.
Install starter button and wire starter button to the relay.
Push the button.
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