Author Topic: 4 speed gears in a 3 speed case  (Read 1512 times)

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Offline tenorhog

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4 speed gears in a 3 speed case
« on: June 30, 2011, 01:36:15 PM »
Anyone done this to their 45?. The guys in Holland are selling it for 700 euro's

I have emailed them for gear ratio's.
Anyone know the origional gear ratio's?
It might be really cool to do unless it's a 1 to 1.
Thanks,  Ben

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Offline PC_Hater

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Re: 4 speed gears in a 3 speed case
« Reply #1 on: August 23, 2012, 06:42:25 AM »
I have looked through the info I have but can't find what the original ratios were.
The usual solution in the UK was to fit a 4 speed Triumph of BSA gearbox. Not rocket science, a bit of faffing about. Mine has had a 1950s Triumph gearbox for many years before I bought it.
If you want to keep the original look then the Dutch 4 speed conversion looks ideal. From old road tests I have read there were some big gaps between the gears so even if the top gear is still 1:1 the change would still be worthwhile. Then you can juggle engine, gearbox, and rear wheel sprockets to get top gear where you want it to be.
My bike does 80mph downhill and cruises happily at 60mph. Plan A is to twiddle the gearing a bit more at some later date.
If you can't find an old British gearbox then let me suggest Quaife Engineeering who do a very nice 5 speed gearbox that fits in place of the old Norton 4 speed gearbox. If you have the money they also do a 6 speed gearbox to replace the old 4 speed. The Norton gearbox was THE one to use. That is why so many UK 45s (and Indians) use Triumph or BSA gearboxes - cheap leftovers from people fitting the Norton box into their BSAs and Triumphs.

I use a belt drive primary on my bike too - works very well indeed.
1942 WLA45 chop, 1999 FLTR(not I), 2000 1200S

Offline 14Frisco

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Re: 4 speed gears in a 3 speed case
« Reply #2 on: August 24, 2012, 12:35:23 PM »
Anyone know the origional gear ratio's?

According to a manual:
Low Gear 2.47:1
Second Gear1.57:1
High Gear1:1

Offline panic

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Re: 4 speed gears in a 3 speed case
« Reply #3 on: August 27, 2013, 07:58:31 AM »
I have some data on that conversion on my site here: