Hi, I am considering buying an M21 outfit . Literature review puts the cruising speed of these to be 45mph. For those with knowledge of this engine,Is there any way to get this up to 55mph , which would hopefully mean you haven't got a stressed out queue of traffic behind you everywhere you go. Thanks
It is possible to increase the engine size so that you can pull a higher gear
The WDM20 site is good for that info. The easy option is to fit a B33 engine. My M33 and Steib outfit will get to 70mph.
I am not sure how much difference increasing capacity beyond 600cc makes and fear there would be diminishing returns the bigger you went requiring twin plugs and other mods to make the most out of it .I thought their may be cylinder head/squish options to increase compression ratio which could improve cruising speed. An extra 10mph doesn't seem like much , but on a wheezy old side valve may be too much to ask.
I have an M33 already but like it as a solo. Good advice about wdm20 site I will have a look at that thanks.
Hello,
How about your M21 sprocket? 17T?19T?
Is there any way you could fit a bit bigger?
Do you ride a lot uphill?
That may be an option, but I am certainly up and down hills a lot.which may be an issue, possibly a case for trial and error!
You only have 15 bhp to play with.you could try welding some of the combustion chamber up to increase the compression a bit. AsI said before all the info is somewhere on the M20WD site.
For such a simple engine design SV's are not easy to tune. You can expend a lot of time and energy for very little return.
It would be far simpler to just get an M33 outfit, with more power from the standard OHV engine.
I have a copy of The Classic Motorcycle, from July '92 where it tests an M33. It quotes a rigid M33 outfit tested in 1950 by The Motorcycle, which says it would cruise at 50-55mph. That's on sidecar gearing, top gear being 5.59:1. The sidecar was the BSA model 22/47, which weighs (says another test) 205lbs.
Below, I've posted another M33 outfit road test. It doesn't give a cruising speed but a bit of maths shows that it would be doing 50mph at 2/3 peak power revs. (It will not get to peak power in top gear)
My previous experience with outfits led to a few liaisons with dry stone walls, so the 45mph might be too fast for me😂.in my defence sidecar was on wrong side driven wheel with diff which meant you lost drive when the sidecar came up, which was a lot on a bad camber and caused it to lurch to the left 😵.
Where were you riding that?
Moldova
No only joking Yorkshire dales.
I did many miles on a plunger A10 outfit in the early 70's. It was my winter commuter in the days when we regularly got ice and snow and also my load hauler for bike parts. While it would hold 60 (or perhaps a little more) it was very hard work. If you set an outfit up for B road camber it doesn't run straight on a modern motorway which is often level or even drains to the right. If you set it up for motorways (ie no camber) its hard on normal roads. I would seldom go above 45 just because of the effort and the problem of braking in a straight line.
Hit the brakes hard at 60 and you change lanes before you get control.
I should add that sustained "fast" cruising with the bars hold against the camber really wears the front tyre out.
45 is more than fast enough ;D