OzVMX Forum

Marque Remarks => British (BSA, Greeves, Triumph etc) => Topic started by: mainline on November 05, 2011, 08:33:01 am

Title: b40wd gearing
Post by: mainline on November 05, 2011, 08:33:01 am

having a look at the standard gear ratios for this engine it seems like 1-3 are fairly low with a bit of a jump to 4th. Should I be looking to swap some of these around for MX use?

1st  -  20.1
2nd  - 15.4
3rd   - 10.03
4th   - 6.53

Title: Re: b40wd gearing
Post by: firko on November 05, 2011, 01:37:26 pm

Those gears look pretty good for starters Paul. I wouldn't worry too much about the 3-4 gap as I doubt you'd be using very much top gear on a motocross course except for maybe parts of Conondale or Barabool. I'd be just making sure the engine's nice and sturdy, with a slight compression step up, perhaps a B50MX profile cam, adecent 28-30mm Amal or flange mount Mikuni on methanol and a B50MX/CCM style exhaust dimensions.

The B40 isn't going to blow away the fire breathing 650/750cc Trumpy's or G85 Matchy's in a straight line but you'll be surprised how quick the little 350 goes. The Cavells and Peter Lawson in WA have had them running up the pointy end over the years. PM sent.

Title: Re: b40wd gearing
Post by: bazza on November 05, 2011, 01:41:33 pm

As Firko says and if budget allows Mikuni helps and electronic ignition is a 2 kick affair.

Title: Re: b40wd gearing
Post by: Davey Crocket on November 05, 2011, 02:49:06 pm

Who are you kidding Paul, you wont even get out of second ;D

Title: Re: b40wd gearing
Post by: mainline on November 05, 2011, 03:56:14 pm

If I run a big enough rear sprocket I might get into 3rd?

Title: Re: b40wd gearing
Post by: LWC82PE on November 05, 2011, 04:18:54 pm

Sorry about the poor scans

(https://blu1.storage.live.com/items/DD4CD6CF9C78622D!754:Scaled1024/GEAR008.JPG?psid=1&ck=0&ex=720)

(https://blu1.storage.live.com/items/DD4CD6CF9C78622D!755:Scaled1024/GEAR009.JPG?psid=1&ck=0&ex=720)

(https://blu1.storage.live.com/items/DD4CD6CF9C78622D!756:Scaled1024/GEAR010.JPG?psid=1&ck=0&ex=720)

The part i did not scan was about the detent leaf springs. Try and get new ones if you can otherwise you can have problems of jumping out of gear.

Title: Re: b40wd gearing
Post by: huskibul on November 05, 2011, 05:51:59 pm

   Theres also a interesting bit of information on set -up and mods for unit single detent springs and camplates on "www.b50.org"  , adds a little bit to     ruperts manual and worth checkin out  :)   

Title: Re: b40wd gearing
Post by: bazza on November 05, 2011, 07:01:49 pm

ruperts manual - should be one on every bed side table

Title: Re: b40wd gearing
Post by: Davey Crocket on November 05, 2011, 07:46:38 pm

Geezus Leith, you've just gone and confused the bugger, he's a chippy, if he cant nail gun it or screw gun it he's stuffed, I know he'll be cowering in the corner. ;D

Title: Re: b40wd gearing
Post by: mainline on November 06, 2011, 07:56:42 pm

Quote from: bazza on November 05, 2011, 07:01:49 pm

ruperts manual - should be one on every bed side table

You know how to keep the ladies happy Bazza  ;) ;D


Thanks for the info guys. I've got the RR manual and have started re-reading it in a bit more depth. The plans are as Firko outlined, a tweak here and there but keep it simple and reliable.

Cheers