WD Motorcycle forum

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Dec 4, 2023 - 12:54AM

Re: Primary sprocket allignment

Micah Leinonen

Hi mark. I thought there was only one oil finger against 1st gear? I’ve been using the dragonfly diagrams as a reference, everything is correct according to that. Everything seems to be perfectly aligned with one 0.010” shim on the main shaft and two 0.010” shims on the layshaft.

I did do something a little unconventional with the selector shaft to reduce the excessive end float. I used a modern motorcycle valve shim inside the bush on the kick start side. I figure it won’t cause any problems though since there is not a lot of movement in that shaft.

The main shaft is flush with the kickstarter ratchet locknut, which makes me think everything is correct lengthwise. I’ve only ridden it once around the block since the rebuild, but it is shifting as good as my modern motorcycles. Whereas before the rebuild, it was a nightmare.

Be careful about having too little end float on the selector shaft. It needs to be able to move. When under load the gear dogs will cause the gears to come a little closer together and if the selector shaft can't move enough to compensate it puts a huge side load on the shifting forks. Eventually the will burn up. It is not something you will generally notice until you see lots of metal in the oil as the bike will shift OK.

That is one reason BSA put an inspection cover on the gearbox.

With the gearbox on the bench, push the gears together in each of the four speeds and make sure the shifting forks have side clearance in the gear dogs.

Micah Leinonen

Dec 4, 2023 - 5:05AM

Re: Primary sprocket allignment

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.

email (option): Micah.leinonen@gmail.com

Ron Pier

Dec 4, 2023 - 6:25AM

Re: Primary sprocket allignment

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

email (option): ronpier@talk21.com

Bruce

Dec 5, 2023 - 7:38AM

Re: Primary sprocket allignment

Hi Micah,

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.

Micah Leinonen

Dec 5, 2023 - 7:48AM

Re: Primary sprocket allignment

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.

email (option): Micah.leinonen@gmail.com

Mark Cook

Dec 5, 2023 - 10:30AM

Re: Primary sprocket allignment

This is a gearbox life extender.

https://pesltd.uk/?product=28-0043

Mark

email (option): pes.sales@btconnect.com

Micah Leinonen

Dec 7, 2023 - 5:14AM

Re: Primary sprocket allignment

I’ve already glued a magnet into my plug but thanks anyway

email (option): Micah.leinonen@gmail.com

Micah Leinonen

Dec 7, 2023 - 5:19AM

Re: Primary sprocket allignment

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.

email (option): Micah.leinonen@gmail.com

Mark Cook

Dec 7, 2023 - 10:19AM

Re: Primary sprocket allignment

If you decide your mounting plates are too much trouble Micah, these work well.

https://pesltd.uk/?product=66-4157

Mark

email (option): pes.sales@btconnect.com

trevor

Dec 8, 2023 - 4:17AM

Re: Primary sprocket allignment

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.

Micah Leinonen

Dec 10, 2023 - 8:48AM

Re: Primary sprocket allignment

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?

email (option): Micah.leinonen@gmail.com

Micah Leinonen

Dec 21, 2023 - 1:23AM

Re: Primary sprocket allignment

I’m pleased to confirm that straight gearbox plates and correct spacers fixed my primary sprocket alignment problem.

email (option): Micah.leinonen@gmail.com

Ron Pier

Dec 21, 2023 - 6:20AM

Re: Primary sprocket allignment

In the parts list for the RAF outfits, a 17T sprocket was used. But they did tend to under gear stuff back then. I think I'd try the 18T. Ron

email (option): ronpier@talk21.com