Almost Ready MK3, Now I'm Scared: Layshaft

I got my 75 Mk3 ready to run, but in following all threads on this good forum I've become aware of the layshaft bearing problem.
I am the original owner, Is there any chance my late 75, SN329404, could have an improved bearing in it?
I put 14000 carefree miles on it up until 1990 and haven't ridden it for 20 years. I guess ignorance is bliss.
But now that I'm not ignorant, I'm scared. That bearing job sounds tough with all the heating, cooling, and pressing going on.
Did ANY of the later models come with the right bearing?
I would appreciate your input and encouragement.



JD

jaydee75 said:

That bearing job sounds tough with all the heating, cooling, and pressing going on.

Click to expand...

It's probably not as difficult a job to do as you may think.

jaydee75 said:

Did ANY of the later models come with the right bearing?

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It seems not. I think just about every forum member who has reported doing the bearing change on their Mk3 (myself included) has found it to have been a Portuguese 6203 brass cage ball bearing, not the roller.

I had never been inside any gearbox until I got my '74 and replaced some bushes and the layshaft in situ. I used the following link to do it and it was not bad. Take your time and take a break if things get tough. I think it is a worthwhile replacement. I used an electric heat gun for my heat source.

Use the OldBritts site for the disassemble, assembly and checklists. They links are in the article below:

http://www.doov.com/apps/nortoncomp...=25:layshaft-bearing-upgrade&catid=1&Itemid=8

drones76 said:

I had never been inside any gearbox until I got my '74 and replaced some bushes and the layshaft in situ. I used the following link to do it and it was not bad. Take your time and take a break if things get tough. I think it is a worthwhile replacement. I used an electric heat gun for my heat source.

Use the OldBritts site for the disassemble, assembly and checklists. They links are in the article below:

http://www.doov.com/apps/nortoncomp...=25:layshaft-bearing-upgrade&catid=1&Itemid=8

Click to expand...

+1. I did it, it's tedious and a bit nerve wracking if you've not been inside a transmission before ( I had not), but it can be done with the info on the above link and the helpful folks here.

BTW, my bike has 333XXX as the VIN numbers, and still had the dreaded bearing, so that should confirm the bad bearing choice up to that VIN number anyway.

Go for it jaydee75, I've yet to do it on my MKIII so I'd follow your layshaft bearing replacement thread with great enthusiasm

Me to! My 6000 mile MK3 as the original. :twisted:

It might be worth noting that although I used the info in the link provided above, I did not use a roller, and instead went with the ball recommended by M Hemmings.

Up to & including removing the old bearing was identical. Note: in contrast to the Old Britts website article (for a total tranny overhaul) one does not need to remove the cam plate and shift quadrant (see the "Free at last" captioned photo in the link to see the cam plate and quadrant undisturbed).

At that point I left the new bearing at room temp and put the layshaft (with old bearing removed) in the freezer overnight. The new bearing was installed with a very light press using a suitably sized socket (sized to fit the inner race) and a bench clamp. If it hadn't of worked I would have run it down to a local garage to use a pro bearing press.

Then, if it is not apparent, one does not have to do the layshaft shimming thing if going back with the improved ball bearing. Otherwise the rest of reassembly followed the link directions.

The hardest part (for me) was getting the gear selector arms engaged with the selector fork spindle and the cam plate when inserting the shafts. I had to move the cam/quadrant into different gears as the parts were reassembled. But as the cam, quadrant, and neutral switch weren't touched, this removes one set of worries.

Don't be put off it's not that hard of a job, I replaced my bearing when I was young at the age of 19 with no experance at all with gear boxes, my bearing blew to peices and found it sitting on the bottom of my gear box, that was in 1978 and I still running the replacememt bearing to this day and well over 120,000 miles on it.

Ashley

I replaced mine after reading all the horror stories on the forum.I did it with the trans in situ and just kept going back
to the directions frrom Old Brits and everything worked out fine.I also did not take the cam plate assembly apart.M/C
had 12000 miles on it at the time.I think it is a good time for you to do this project if for nothing else but peace of mind.
You will end up enjoying your motorcycle more than ever.Just my 2 cents
Mike

Ok, I'm starting the job tomorrow.
How did you in situ guys do it? I'd like to raise the bike to be able to access it better. Or maybe lay it on its side.
Any ideas?
JD

Some engines like Combat need to be released enough to tip way up/forward to allow gear box to rotate forward enough to clear the cradle cut out. Tempting in a way to get into the engine once that close to removal, but another subject.

Primary crank puller needed with good torch and 1.5" end wrench or welded up deep socket to get the reverse threaded counter sprocket off. Small wedges are handy to lock up clutch and its center. Realize once drive chain off no other way to lock up some stages of torquing stuff on/off.

I've had a few lay bearing races be a bugger tight to get on off but once done all was well. There is no need of any gaskets in the shell so I've stopped using them and seems to automatically solve the lay shaft shim to kicker slack issues. Search up the kicker oil seal upgrade methods, DIY simple to send off for machining.

Bushes are weakest links especially the 1st gear paper thin one and the sleeve bushes. Only short sleeve bushes should have a spare one in middle to space the load bearing one far apart but new long kind only need a pair. I oil groove these as oil slings out in lower gears, so helps refill at stops and in 4th.

Some do the whole job with shell inside but all that bending head and reaching out, to me easier to have it out on bench- especially first time, then its seems so simple - eventually. Pay close attention to how close the cam shifter fork-dowel thingy is to edge of case if that taken apart. Outter cover pawl spring needs its legs parallel to the pawl and just close/far enough the pawl swign clears then can measure if ya like to see how close to manual specs it is but waste of time trying to match manual if it works it works or good risk getting the spring legs out of parallel yet not showing up til on the road missing shifts altogether.

Then should look up how to nail down kicker lever for a while.

Although you can use a ball bearing ,shy away and purchase the Roller. Think of the forces involved on the drive side. Enjoy the process and take breaks. Do it with gearbox in bike ,no probs there with heatgun best option and frozen bearing should just drop in place with gentle taps around outer race. It's fun and wear rubber gloves as oils = cancer now ,good luck. Peter.

"In situ" means transmission stays in. No need to take apart the drive side. (If you are lucky.)

jaydee75 said:

Ok, I'm starting the job tomorrow.
How did you in situ guys do it? I'd like to raise the bike to be able to access it better. Or maybe lay it on its side.
Any ideas?
JD

Click to expand...

I did mine while it was on the center stand or maybe the sidestand, although if you can raise it up some, your back will thank you. I now have a foot pump motorcycle lift. It is heaven compared to the cold nights laying on the floor or bent over sitting on a milk crate. Raise it up. I think I would find laying it on its side to be cumbersome to work on it.

Nothing to worry about . If youre thrashing it in the Mountains and the kick start starts knocking holes in the back of youre calf , pull over immediately .

Another option is to pull over immediately after the rear wheel locks up with a truck on your ass.

Ok, I'm making progress. I blocked the bike up 6" on the centerstand. It helps a lot with access.
I've got the outer cover off and everything looks real clean and good. There is one rusty bolthead for some reason.
Now, I want to replace the bearing without disassembling anything unnecessary, so I'm wondering if I can remove the inner cover without removing the clutch operating lever body that requires a special tool. It looks like if I remove the cable pawl, the cover may slide off over the big shaft. Will it?
Here's a couple of pics:
JD

Old Brits has the info on how to do this, use it. You don't need to take the cam plate out. Take lots of pics for reference when putting it back together.
Good luck

Ugh, you taken/gotten most the short cuts ya can by quizing us and by leaving bike on floor and shell in cradle. Ya don't need a special tool to handle the cable end gizmo - just just a whammer and blunt-ish drift and maybe some heat around it if it don't move before the metal dings up. Its a slip ring type arrangement, Ring bolt snugs around the lever gizmo to nail it down in best alignment to cable. A knife edge mark helps on nipping it back up. Oh yes it must come off to got deeper.

Some make up their own tool or buy Norton's but it should not be crazy tight to require it, just easier faster to un-do and re-do on the mark. I done it like 4-5x's now w/o the tool and so have 1000's before and after me.

The oil level and splash never gets to the rusted bolt you saw and you lucked out that's all you find rusted but can seriously rust up the pawl spring mount and swell bolts threads for mean removal. I now spray paint clear coat on those for the long term.

jaydee75 said:

I can remove the inner cover without removing the clutch operating lever body that requires a special tool.

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No, because the nut has to be removed from the end of the main shaft.

The ring can be removed/refitted using a hammer and punch, in fact, that's the way Mick Hemmings says he prefers to do it.