After the weekends pre-war landsrace (1/8 mile), i realised that more power is needed.
My M21 is a 1939/40 fittet with steel flywheel and with a sligthly bigger bore given approx. 620 ccm. (piston type unknown)
A R57 racing amal carb (30 mm / 1-3/16") is fitted and the inlet bore is also made 30 mm to fit. The cast iron cylinderhead is welded up to raise compression and finnaly a radius is made at top of the cylinder bore aligned with the inlet valve to get better flow.
As i did above modification, i also replaced all bearings + big end ect.
Next thing to do could be install other cams - However - opposite the sidevalve VLA/C Harley Davidson, You just can´t buy racing cams for M20 / M21. An alternative could be Goldstar touring cams but after a lot of reading I find it difficult to conclude wheter there is a benefit together with above modification or not, having in mind that SV and OHV are two different things. Has anyone tried Goldstar touring cams with improved result ? - or has any one better ideas for getting more power?
Thanks in advance / Best regards Per / Denmark
email (option): pergarbos@gmail.com
Contact me off forum on this one...It's really about how much work you are prepared to do, though it sounds like you've done quite a bit already...Ian
email (option): ian@wright52.plus.com
I run GS touring cams in the previous M20 engine
While they push peak torque a bit up the rev range I don't think they gave much more useful power as what they gave at the top they steal from the bottom.
I run a concentric with a long induction manifold such that the air filter has to be dissasembled to remove it
That did make the bottom end more smooth and helped throttle response as much as it can be responsive with the massive flywheels .
Shifting the plug over the top of the piston made a noticeable difference to a friends M20 as it allowed him to shape better induction & exhaust tracks in the head some thing that had been on my to do list for a long while but I put the B44 on the road insted .
The Victory Libraries have a lot of tuning ideas for M20's which will be applicable to M21's
Swapping the breather over to the timing chest is good & running a through breather , in through the standard outlet & out via the timing chest is eve better & will give you around another 1/2 horse.
But if you go that way you must fit oil seals on the crank .
['Swapping the breather over to the timing chest is good & running a through breather , in through the standard outlet & out via the timing chest is eve better & will give you around another 1/2 horse.
But if you go that way you must fit oil seals on the crank ....']
I don't understand the benefit of that...The crankcase breather is designed to open on the downward stroke to vent and relieve crankcase pressure built up from blow by past the rings on the combustion stroke and to close on the upward stroke to reduce the amount of air being moved (sucked back in) by the pumping effect of the piston as it cycles through its stroke...The reduction in crnk case pressure and air movement thus reduces mechanical pumping losses...If the piston is allowed to draw the full amount of air into the crankcase on every stroke how would that be beneficial and how would it gain power?....Also, there would seem to be little point fitting seals to the crankcase if there is unimpeded movement of air through the 'inward' breather...Ian
email (option): ian@wright52.plus.com
If Rex Bunns blog is still up then it is all there.
Auckland University eventually ook up the challenge & did a lot work on crankcase breathing on motorcycle engines .
Remember the original design is supposed to pump down the crankcase to around 1/2 atmosphere and maintain that vacuum to prevent oil leaking out past the scrolls & flingers.
THis takes energy, a lot more than I would have thought .
Through breathing requires almost no energy and that enegy s then available to the crank
Some historic recers running side valve HD's claim the got anything from 0.25 to 1.5 Hp increase at the crank by through breathing with Rexes very responsive check valve each end.
A standard check valve produced slightly less increase.
And apparently you can tune the check valves so they work most efficiently within a particular rev range
What I do know is the B50 & B33 both bcame 100% oil tight when I set them up for through breathing .
If you want to circumvent BSA's clever oiling, feel free to stick holes and valve where ever you want. It's not always obvious what BSA intended.
I read this rex bunt stuff many years ago and was not convinced.
If you have considered every aspect of the engines lubrication system, stick the biggest hole in the crankcase that you can connect a hose and filter too. This will pick up a little power at lower rpm. Gases don't like changing direction at high speed.
Fill a jar with some aerated oil in it, then apply a small vacuum and watch it grow.
Gear oil pumps are not good at pumping air, so it's unwise to make the oil pumps job harder by applying a vacuum to the crankcase.
Then if you are successful in achieving this vacuum, you will be pulling dirt into your engine from the places it normally weeps.
If I every own an eddy-current dyno I might play around with this to prove my theories, or disprove as the case may be.
BSA did move the breather to the righthand side on later engines? Has anyone got any documentation on this?
email (option): pes.sales@btconnect.com
Bsa moved the location of the breather a number of times on B and M Series engines (3)...Also the flap valve fitting was modified three times and the timing cover and breather housing pipe were altered twice and three times respectively when the breather was in the timing cover...Sidevalve and OHV motors also had different diameter breather vent pipes and fittings with two different ones on the 'M' models over the years...
Apart from the breather function itself I know there were problems with the timing cover mounted breather passing too much oil....The breather situation peaked out on later WB30 models which had a total of four breathers...On the later Gold Stars the flap valve didn't know whether it was coming or going at higher revs so a timed breather was fitted to those models...Ian
email (option): ian@wright52.plus.com
This part will help!
http://www.stevenott.com/gruppovelox.htm
I rebuilt a Gruppo Velox engin for a friend which now resides in a Goldie 'lookalike'...There were a number of compromises to get the OHV top end onto the M20 and other ex WD models....The head has really good ports so there is potential but some re engineering would be required to make it go as well as it looks...Ian
email (option): ian@wright52.plus.com
Shove a B33 engine in it....
email (option): jeremy@clogmaker.co.uk
If it was just about performance without any other considerations swapping out the engine, or even half of it, would be the obvious option. After all, sidevalves of this era were basically glorified stationary engines that someone decided to fit wheels to...Taking that idea further it would be quite straight forward to get an A10 engine into the frame...
However, the fun and the challenge is to get some meaninful improvements from a design that wasn't meant to go that well in the first place...:laughing: The dark art of tuning side valves awaits....Much more interesting and considerably more difficult than tuning an OHV engine in my experience...Ian
email (option): ian@wright52.plus.com
Thanks a lot for all the feed back and the advices. Camshaft design is most likely extremly complicated as the design has to interact with so many unknown factors. Its great to know that touring cams takes in the lower end and gives at higher rpm.
Long induction manifold and mowing the sparkplug are interesting issues with focus on better performance. Normally i would only consider moving the sparkplug due to higher lift of inlet valve.
As i want stick to pre-war parts the only solution for an OHV, would be a M22 engine but at the other hand its also interesting to optimize the sidevalve design. Have to mentioned that The M21 is used for pre-war landrace so no matter what, a B33 or a Gruppo velox conversion is not an option - I have actually never seen a Gruppo velox kit so these are most likelly very very rare.
The current breather system is similar to many other singles (AJS and Matchless competition) so even there might be room for improvement i think i will keep it as it is - at least for now.
Thanks for feed back / best regards Per
email (option): pergarbos@gmail.com
Here's one...A nice looking engine...The conversion was fitted to Norton 16Hs and Triumph 3HWs as well as M20s.......Ian
email (option): ian@wright52.plus.com
Thanks for the illustration, nice looking design. In my opinion it was acually not a bad idea to offer OHV conversion kits most sidevale WD motorcycles. However - since its the first time i hear about Gruppo Velox it must be very rare, and due to that - not a big sale succes. I found another picture and even i am not sure, it looks like the rockers are incorporated in the cylinderhead - just like it was at the more modern BSA A65.
email (option): pergarbos@gmail.com