I am mystified - Not unusual. Doing a conversion from 425 to 605 and was going to keep the 6 Volt starter, but run it on 12 Volt. Done most of the other 6 to 12 volt changes, but the starter will not engage. There are all sorts of gear mashing noises, the starter spins, but will not engage. When I connect the starter on a 6volt battery, it engages lovely on the 605 engine.

Where am I going wrong ?

Bobh,
daft question maybe, but is the polarity correct when you've hooked up that 12 volt battery?

Only other thing I can think of is that with 12 volts, the 6 volt starter's pinion is being spooled up so quickly that it just doesn't have a chance of engaging with the flywheel teeth as it moves forwards.

Have you tried switching on the headlights, brake lights and anything else which would pull down the battery voltage before you hit the start button?

ken

Which begs the question. What sort of resister can be installed reducing the voltage to 7 volts.
Same for fiiting a 6 volt wiper motor on 12 volt system?

Unfortunately, it's not as easy as just popping a resistor in series with the supply from the battery, as the value of the resistor required would vary with the amount of current being drawn if there is more than one item to be fed from the resistor.

Check out this VW Beetle site for more info.
http://www.ssvc.org.uk/phpbb/viewtopic. ... w=previous

If the resistance of a 6 volt wiper motor is close to that of a 2CV motor, it might be worth a shot at the 'cheap and nasty' method, which uses one of these power resistors.
http://www.paruzzi.com/webstore/?zoektrefwoord=2414

Of course, they can be found cheaper...
http://www.ebay.com/itm/EMPI-9384-VW-BU ... 0409800284
& even lower, if you go for a handful of the bugg@rs...
http://www.ebay.co.uk/itm/5pcs-4-Ohm-4R ... 917&_uhb=1

ken

Ken, battery round the right way, adjusted the contact so that the pinion would be closer to engagement before the power came on to no avail. Don't think the resistor idea would work. I think you would need something like a 1000watt resistor. Probably easier to lengthen the feed cable so it was about 50meters long. Another idea is to make a centre tap on the 12volt battery, so the starter ran at 6volts. Re-position the equipment feed cable(s) to come directly from the battery positive. Easier to change the starter.

trouble is modern batterys cant be centre tapped like in the old days when they had lead links on top
best to get a 12v motor as u say
btw,be careful not to damage the ringear

got a 12 volt starter for 25euro from www.leboncoin.fr works just fine, so goodbye 6volt. Bonus, the engagement lever (its a pull starter not solenoid) is almost horizontal, clearing the air filter.