Re: M21 needs more power -any advise (if my subject not is relevant - please remove
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?
Re: M21 needs more power -any advise (if my subject not is relevant - please remove
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
Re: M21 needs more power -any advise (if my subject not is relevant - please remove
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
Re: M21 needs more power -any advise (if my subject not is relevant - please remove
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
Re: M21 needs more power -any advise (if my subject not is relevant - please remove
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.
Re: M21 needs more power -any advise (if my subject not is relevant - please remove
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.