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Kent Shaun
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How to get a m21 to go fast(er) ? #514819
11/15/13 9:39 pm
11/15/13 9:39 pm
Joined: Nov 2013
Posts: 4
Sweden
G
Gustaf Offline OP
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Gustaf  Offline OP
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Joined: Nov 2013
Posts: 4
Sweden
Hi, i have allways had a thing for flatheads and the challenge to get more speed out of them.
I have a harley wlc 750 and i know that with stroker flywheels,big bore and sportster cams and connecting rods you will get a good 1100cc and alot more power...
Now i have a bsa wm21 and wondering what can i do to increase the performance and speed other than the obvious (get another bike), someone told they have seen a 900stroker m21 ?

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Re: How to get a m21 to go fast(er) ? [Re: Gustaf] #514848
11/16/13 5:50 am
11/16/13 5:50 am
Joined: May 2013
Posts: 4,765
Rotherham - S. Yorkshire
Allan Gill Offline

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Allan Gill  Offline

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Joined: May 2013
Posts: 4,765
Rotherham - S. Yorkshire
Kent Shaun. Welded up half the combustion chamber on an iron head. You could also go for a taller sprocket setup to make use out of your new found power? Increase. Goldie cams but it will need some modifying. Larger carb with a taper down to the stock size just after the carb and a extended inlet track. Best shouting on the rod and Tappet as there's where Shaun and Bazza hang out.

You'll never be A10 performance. But you will have fun doing it.


beerchug
Re: How to get a m21 to go fast(er) ? [Re: Gustaf] #514850
11/16/13 6:31 am
11/16/13 6:31 am
Joined: Dec 2004
Posts: 9,224
Scotland
kommando Online content
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kommando  Online Content
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Joined: Dec 2004
Posts: 9,224
Scotland
Try looking here

http://www.eBay.co.uk/itm/BSA-M20-Based-Vintage-Sprint-Race-Hill-Climb-Bike-/190530142884?nma=true&si=IqSL6wf9LAxlDT%252BGFARsF174bik%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

Difficult to do justice to the description of this rather special Machine. Owned by me for the last few years and used mainly for Sprinting in the Vintage Class.

The machine was featured in the May 2002 Classic Bike Guide with a 5 Page article on its origins and development. (A copy of the Article will be included in the Sale.) See Pictures.

Sadly, I have other projects to finish and it is time to move it on. If you are looking for something different and are up for bit of excitement, this could be for you!

Based on the immensely strong M20 Machine (The Dispatch Rider's Work Horse) this machine is made up of a real variety of Pre & Post War parts. M20's were 500cc but this has had the 600cc M21 Flywheel/Rod arrangement fitted giving a Stroke of 112mm. To further increase the capacity, the Barrel has been Bored out to 92mm and fitted with a very robust Piston from a Volkswagon Beetle! This gives a capacity approaching 750cc. Whilst the humble Side Valve arrangement and very long Stroke does not lend itself to very High Rev's, it certainly makes up for it in sheer 'Grunt!' It has run in the Pre-'46 Class at Vintage Sprints and has stunned people who traditionally regard Side Valve Machines as 'Slow Plodding Sidecar Tugs'. Do not under-estimate the Side Valve machine. Remember the early Transatlantic Match Races? The USA Team came over with their big S/V Harley's and won Races here against some of Britain's finest! So good were those S/V Harley's, I am led to believe that the Cam design has been replicated in this BSA!

This is far from a Concours machine as its prime function is to 'GO, not 'SHOW', however it always attracts a lot of attention being so unusual. I have run it mainly on Methanol but it has been jetted to run on Petrol in an attempt to win a 'Petrol' Award. I am happy to include the Methanol Jets in the sale. Be aware that the riding style is quite unique for a Race Bike in as much as you don't need to rev it to make it go! It has so much low down power that it can (and has) lifted the front wheel in 3rd Gear! It has been timed at close to 100 mph at the end of a Flying Quarter Mile. Being light for a machine of this capacity, it is also ideal for Twisty Sprints and Hill Climbs.

As a pure out and out Race Machine, there are obviously no Documents (V5's etc.) and it is obviously not Road Legal!

I will try and list the parts I know:

Early B31 Rigid Main Frame (Modified Rear End) - Much Modified M20 Engine with 90 x 112 Bore & Stroke - Head Reworked/Flowed with repositioned Plug - Barrel with Ports opened up and Flowed - 32mm Carb currently jetted for Petrol - STD BSA Gearbox with Wide Ratio's suitable for the mass of Torque on tap and fitted with Norton Clutch - Royal Enfield Lightweight Girder Forks (With Supplemented Side Springs and extra Bracing) fitted with Steering Damper and Compression Damping - BSA Hubs with Alloy Rims (18") - Tubular 'Sprint' Tank with integral Oil Tank - Ace Handlebars and Rear-Set Footrests - Open Pipe (Tuned Length) with Leg Protector

Re: How to get a m21 to go fast(er) ? [Re: Gustaf] #514938
11/17/13 12:03 am
11/17/13 12:03 am
Joined: Jul 2009
Posts: 3,549
Vic. Australia
P
Pete R - R.I.P. Offline
In Remembrance
Pete R - R.I.P.  Offline
In Remembrance
P
Joined: Jul 2009
Posts: 3,549
Vic. Australia
Increasing the bore and stroke will only increase the compression slightly.Apart from that,you can expect much the same power but at lower rpm.

To make power,you need to feed the engine.Cams from an ohv engine would help. Faster M21

Re: How to get a m21 to go fast(er) ? [Re: Gustaf] #515007
11/17/13 3:00 pm
11/17/13 3:00 pm
Joined: Nov 2013
Posts: 4
Sweden
G
Gustaf Offline OP
BritBike Forum member
Gustaf  Offline OP
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Joined: Nov 2013
Posts: 4
Sweden
Thanks guys, didnt see the other thread before i started this, much useful info on there ! Anyone knows what you must do to fit the goldie cams in the flatty?

Re: How to get a m21 to go fast(er) ? [Re: Gustaf] #515046
11/17/13 6:45 pm
11/17/13 6:45 pm
Joined: Aug 2013
Posts: 495
Australia
D
downhere Offline
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downhere  Offline
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D
Joined: Aug 2013
Posts: 495
Australia
Just weld your heads up to these K model shapes!

Re: How to get a m21 to go fast(er) ? [Re: Gustaf] #515047
11/17/13 6:47 pm
11/17/13 6:47 pm
Joined: Aug 2013
Posts: 495
Australia
D
downhere Offline
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downhere  Offline
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D
Joined: Aug 2013
Posts: 495
Australia
Or this Ricardo shape!

Re: How to get a m21 to go fast(er) ? [Re: Gustaf] #515048
11/17/13 6:51 pm
11/17/13 6:51 pm
Joined: Aug 2013
Posts: 495
Australia
D
downhere Offline
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downhere  Offline
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D
Joined: Aug 2013
Posts: 495
Australia
Even this roughly welded up version gave an extra 10 mph!

Re: How to get a m21 to go fast(er) ? [Re: downhere] #516178
11/25/13 9:51 pm
11/25/13 9:51 pm
Joined: Nov 2013
Posts: 4
Sweden
G
Gustaf Offline OP
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Gustaf  Offline OP
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G
Joined: Nov 2013
Posts: 4
Sweden
Thanks for the inputs ,Yeah with my lack of tools this is probably what ill ending up with if i do it myself you have any description on the heads as far as the shapes goes
And again anyone knows what work must be done to get the goldie cams to fit / Gustaf.

Re: How to get a m21 to go fast(er) ? [Re: Gustaf] #517026
12/01/13 7:51 pm
12/01/13 7:51 pm
Joined: Nov 2013
Posts: 4
Sweden
G
Gustaf Offline OP
BritBike Forum member
Gustaf  Offline OP
BritBike Forum member
G
Joined: Nov 2013
Posts: 4
Sweden
Hohoo?

Re: How to get a m21 to go fast(er) ? [Re: Gustaf] #517058
12/02/13 1:42 am
12/02/13 1:42 am
Joined: May 2009
Posts: 86
Australia
M
MattL Offline
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MattL  Offline
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M
Joined: May 2009
Posts: 86
Australia


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