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WM20 Gearbox Problem

I am in the process of TRYING to rebuild the gearbox with NOS parts .Unfortunately hit a problem the 1st & 2nd gear will not press onto the NOS shaft .I used a puller to remove the gear off the old shaft by using finger pressure .

I put the shaft in the Freezer overnight and warmed the gear in the oven............. used a 10T press and it goes on approx 14" of an inch and will not move any further :confused: . In the photo you can see the mark on the shaft where the gear actually gets to .

I think I need to get the gearbox to an expert to do the job, not conversant with the pitfalls on the WM20 , so if anyone knows of where I can send it , it would be much appreciated :grin:

I've measured the new shaft which is 23.82mm
Old Shaft 23.72mm

I thought this would have gone but the press was putting some serious pressure on and I don't want to damage the new shaft







Thanks

Dave

email (option): davemb42@yahoo.com

Re: WM20 Gearbox Problem

Type error....... 1/4" of an inch not 14"

email (option): davemb42@yahoo.com

Re: WM20 Gearbox Problem

The 'fixed' gears are a heavy interference fit onto the shafts and consequently require a lot of pressure to fit them...Using a hydraulic press they will usually 'squeak' as they are pressed on....It can be worrying but as long as they are going on square it should be OK...

As you have new components you obviously have the full interference...Used components can vary from sliding freely by hand through to the correct fit, depending on the amount of use/abuse they have had and how many times they have been removed and replaced...As such they are not a good guide to the required fit which, as noted, is a heavy fit...Ian

email (option): ian@wright52.plus.com

Re: WM20 Gearbox Problem

Thanks Ian. I was getting a bit worried with amount of pressure that was being applied and nothing seemed to be happening .As I say the gear came off the old shaft very easy but didn't want to know on the new shaft .

I'll get the shaft back in the freezer and try again tomorrow , fingers crossed .I have the layshaft to replace too .

I was going to replace the selector shaft but saw the "rivets" had been peened over at the back and unfortunately I don't have the new "rivet", so I might leave that one alone before I end up the creek without a paddle.

Thanks

Dave

email (option): davemb42@yahoo.com

Re: WM20 Gearbox Problem

The difference between the dimensions of the two shafts (.1mm or .004") is a lot! Which dimension is the correct one? I am guessing the smaller one.

I am always supecious of NOS parts as on a few occasions (not just BSA) you find out after having bought the part the reason it was sitting on the shelf unused for many years as it was made wrong.

I currently have a NOS Triumph pre-unit clutch basket I bought a few months ago still wrapped in paper that the bearing race was ground too big by about .012". So now I know why it was NOS after 50 years. Also have a NOS BSA M21 output gear where the splines were made wrong and the drive chain sprocket won't fit.

Re: WM20 Gearbox Problem

Stop, the difference between the dimensions of the two shafts (.1mm or .004") is a lot! Which dimension is the correct one? I am guessing the smaller one. Unless there is evidence of .004" wear on the old shaft. Something is wrong.

I am always supecious of NOS parts as on a few occasions (not just BSA) you find out after having bought the part the reason it was sitting on the shelf unused for many years as it was made wrong.

I currently have a NOS Triumph pre-unit clutch basket I bought a few months ago still wrapped in paper that the bearing race was ground too big by about .012". So now I know why it was NOS after 50 years. Also have a NOS BSA M21 output gear where the splines were made wrong and the drive chain sprocket won't fit.

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