Hi Bruce, thanks for that info. Wouldn’t the side load only be momentarily during gear selection? How much end float is recommended? Is it something you can feel when it’s not optimal?
I did it about a month ago but from memory there is definitely good clearance on 4th and second, I can’t remember 1st and 2nd (1st is hard to see), but given that I packed it on the kick start side, this pushing the shaft towards the clutch side (2nd and 4th left of the dogs) I sthould be ok. I set it up with .010” end float with the gasket, i used a gasket sealer which may add a little more but it’s back in the bike now so hard to measure. I’ll be sure to check the oil once I take it for a spin.
I set my end float on all three shafts, at near zero end float without a gasket. The original gaskets are 7 thou. So once the gasket is installed I'm happy with 7-10 thou end float. Ron
Yes if all is shimmed correctly the shifting forks will only see a side load when changing gears. Once you are in gear the shifting forks should be doing nothing and should be free to move side to side a little bit. If they can't move a little bit they are rubbing on the the gear dog clutch and will wear out as they are not allowing the gear dogs to fully engage.
What Ron recommends is correct for shimming but you still need to look inside the gearbox to see what is happening.
I will say it again, THERE IS A REASON BSA PUT AN INSPECTION COVER ON THE GEARBOX! SO YOU CAN SEE WHAT IS HAPPENING INSIDE. IF JUST HAVING IT SHIMMED CORRECTLY WAS ALL THAT WAS NEEDED, BSA WOULD NO HAVE SPENT THE MONEY TO PUT THE INSPECTION COVER ON THE GEARBOX!
Here in the USA the M20 is not as common as in Europe, and especially the UK. But we have lots of rigid and plunger B series with this gearbox. Almost all I have seen are a disaster due to incorrectly assembly. Absolutely no one here ever looks in the inspection cover to see if they put it together correctly and wonder why the gearbox does not work.
I removed the oil tank today and checked it, there’s no problem as far as I can tell. End float is .010” on layshaft and selector shaft. I’m feeling pretty confident with it, but I’ll keep an eye on the oil anyway. I’ve ordered some magnets for the sup plugs to make it easier to check.
I may have found the problem. My gearbox mounting plates have a nasty bow in them. And although my spacers are in the correct orientation, it appears as if 2 of them have been ground down. I’m going to try and straighten them and order the correct size spacers and hopefully this will fix the problem.
measure the width of the mounting lugs on your gearbox
good chance some one has fitted the early narrow box where a latter wide box should be fitted.
read the article in the technical section.
The mounting lugs are exactly 2.5” which I think is right. The frame section that attaches to the plates is slightly less at 2.475”. Should I shim it or was that intentional?