As it is Sunday today I spent the day 'messing about' in the workshop and decided to take a look at a damaged gearbox cover. As is frequently the case the kickstart bush boss had cracked....
So, I made up a jig to hold the gearbox cover in the lathe and machined down the outside diameter of the cracked boss.
Next I turned up a steel ring and pressed it over the boss. The cracks can clearly be seen in the photo below but the steel ring should stabilise the boss and prevent any 'opening up' of the cracks under load...Doesn't sound much but I was hard at it all day!
Theoretically it should be a solution that can be used to redeem damaged casings...Ian
email (option): ian@wright52.plus.com
Very impressed Ian! A nice, simple bit of Sunday afternoon tinkering, which in theory, should be stronger than the original? I likes it. 
Hi Mick, Quite possibly, I'll have to do a couple more and see how long they take me to do. Today I had to make the jig for holding the cover, make a lathe tool to get into the restricted space and also remove the 'gap' bed on my lathe, which took a while as it may never have been out previously...Also, you tend to go slowly on the first one! I would probably get a batch of the 'rings' made as well...it would be quicker and cheaper to get someone with production facilities to make them and then just machine the covers to suit the rings..It would also be more sensible to do a few at a time...that way the set up time would be spread over more parts....Ian
email (option): ian@wright52.plus.com
Hi Ian,how many rings do you want?,send me the sizes and you may get lucky.
cheers Rick
email (option): richardholt@rocketmail.com
Hi Rick...I'll work it out...To be honest with this first one I more or less 'made to suit' as I went along without recording all the dimensions..
Michiel...The boss is tapered from the top to the base at the back of the cover. The base area is the strongest part and I have left that untouched.
I turned down the boss to reduce the outside diameter along part of its length and then machined the sleeve to suit and pressed it on.
At the top it is a slightly larger diameter than the original boss but the kickstart spring fits over it OK...further down, the sleeves outside diameter matches the outer diameter of the original boss as it meets the remaining tapered part of that...
If there are any operational problems with spring clearance at the upper end it is a simple matter to taper the sleeve slightly on its outside diameter, though I don't think there will be.
I made the sleeve a moderately 'light' press fit as I didn't want to 'crush' the boss and compromise the fit of the kickstart bush. Because of this I did, in fact, use bearing fit Loctite as well, as an 'insurance' against any movement...Ian
email (option): ian@wright52.plus.com
Hi Ian,
I was asking because I wondered if the boss could be made thicker why BSA didn't do that in the first place... (cut down on material costs ??)
In the early 30's design there is much more material round the base of the boss and the boss protrudes not as far as the M20's, although the steel bush is the same. BSA added an extra coil to the kickstartspring somewhere in the mid/late 30's which explains the larger protrusion but sadly it turned out not to be as robust as it was designed in the first place...
Here is a picture of an early handchangecover, no ribs but less protruded and much more material on the outside:
Anyway, thanks for sharing your idea. Regards, Michiel
email (option): m.wijbenga@hotmail.com
Hi Michiel..Another thing to consider is that it may never have been a problem at the time...It may be 60-70 years of use that has lead to the failures..Ian
email (option): ian@wright52.plus.com
Built in obsolescence !
If only modern products had such built in obsolescence....