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BSA WM20 more power.


Ron
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Some years ago I installed an M21 crank and +40 piston to increase my engine size to about 600cc and increased the engine sprocket from 19T to 20T. I had tried a 21T but found it a bit tall for my likings (a lot more 3rd gear work around 30 mph zones) A couple of years ago I acquired a genuine new BSA B33 "long Conrod" 85mm piston from a guy in Hawaii who had bought it by mistake for his M20 engine. I found him a genuine NOS M20 piston and we did a swap. I've just had my barrel bored out the extra 2+ mm which now gives me 635cc. I'll say at this point that it's not about speed. 50mph is comfortable for me, but it is good to have the extra acceleration and pulling power on hills.

While the tank was off, I resprayed it but managed to preserve the unit markings that were hand painted by a departed friend and for the first time in my 35 year ownership, it's got its correct C number. I've also fitted my freshly restored Talflow filter .....Just for something different. The few original B&W pictures of a Talflow on an M20  I've looked at, show something akin to the Vokes protection pad that is well documented, so I'm going to make something with a certain amount of artistic license.  Ron

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Talflows 2 (2).jpg

Edited by Ron
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Posted (edited)

The vokes became standard factory fitted in 1944 I think. I think the Talflows were shipped out east and fitted as required. 

Here are a few more Talflow equipped M20's 

Ive clocked up 100 miles over the last 3 days. Ron 

Talflows 3.png

Talflows 4 Tommy-in-Burma.jpg

Edited by Ron
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Vokes filters were pioneered by Norton, already in 1937! but the War Office wasn't really interested, until the North Africa and Far east campains got underway, but by the time the contracts were made for Vokes and Talflow fitted bikes, and the bikes were produced the war was almost over!

More can be read here: Air Cleaners (wdnorton.nl)  But don't agree to all what Rob writes.

Below first contract 1938 Norton Big 4, with Vokes.

Lex

PS, still have a couple of Vokes and Talflows for sale.

PROTOT~3.JPG

Edited by welbike
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  • 4 weeks later...

Cheers Steve. You asked in a previous post about "top speed" The truth is, I don't know and not brave enough to find out. I once gave it a burn on a quiet dual carriageway in it's 600cc state and got quite easily up to 60mph ......But chickened out at that. These long stroke SV's are more about slogging power than speed. A modern Chinese 125 would probably pee all over me?  Ron

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