Gearbox Post Mortem

Stirlingmoz

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I can’t progress the green laner project until the carb bodies come back from vapour blasting and saw this gearbox on eBay.

I thought it was worth a punt at £40 for the parts alone.

Sellers description

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It arrived this morning and I couldn’t resist a quick peak.

It did turn, albeit making some horrible noises and a rough grinding feel and all 5 gears could be selected..

IMG_5235.jpeg
 
Got it open and on first inspection, the rear bearing on the output shaft has collapsed.

Not sure how the outer bearing is still with the inner ! Everything inside has a silvery sheen and the magnetic drain plug is a Christmas tree of shavings..

IMG_5239.jpeg

It’s going to need new bearings all round at the very least but I’m hopeful it’s saveable.

More strippage, cleaning and assessment of what’s left to follow..
 
Stirlingmoz said:
Got it open and on first inspection, the rear bearing on the output shaft has collapsed.

Not sure how the outer bearing is still with the inner ! Everything inside has a silvery sheen and the magnetic drain plug is a Christmas tree of shavings..

View attachment 543054

It’s going to need new bearings all round at the very least but I’m hopeful it’s saveable.

More strippage, cleaning and assessment of what’s left to follow..
Click to expand...
LUCKY BUGGER LOL

#WinnerWinnerChickenDinner
 
Been giving this gearbox repair some more thought.

I find the clutch pull on this /5 engine (heavy flywheel) with /6 gearbox quite heavy these days, especially on longer rides or trips into London.

IMG_5242.jpeg

Thinking I could convert it to run a post 81 flywheel & clutch, resulting in a lighter pull at the lever.

As this gearbox case has minor damage anyway, I could refurb the internals and drop them into a pre 81 /6 smooth case to better match the early engine.

Means tracking down more parts but I’m in no rush.
 
Finished stripping the gearbox this morning

IMG_5244.jpeg

The bearings on the output shaft are really bad and I think the filings have got into the other bearings and gear clusters.

It’s going to have to fully come apart for cleaning and bearing replacement.

This is some of the metallic sludge sitting behind the bearings..

IMG_5245.jpeg

Output shaft doesn’t have a circlip (or groove) to retain the front bearing

IMG_5246.jpeg

And lastly this morning, I cleaned the rear cover with a wire brush and some WD40.

IMG_5247.jpeg
 
Stirlingmoz said:
Been giving this gearbox repair some more thought.

I find the clutch pull on this /5 engine (heavy flywheel) with /6 gearbox quite heavy these days, especially on longer rides or trips into London.

View attachment 543122

Thinking I could convert it to run a post 81 flywheel & clutch, resulting in a lighter pull at the lever.

As this gearbox case has minor damage anyway, I could refurb the internals and drop them into a pre 81 /6 smooth case to better match the early engine.

Means tracking down more parts but I’m in no rush.
Click to expand...
Take your time Pete, just tell me when to collect her once you have finished with “my” bike! ….:)
 
Still trying to source a smooth gearbox case to rebuild this into, but just received a shifter mechanism refurb kit from Motobins.

A good kit in my view as it contains all the springs, clips needed for a rebuild, plus a bearing to replace the nylon detent roller.

IMG_5269.jpeg

Definitely worth stripping and cleaning as the oil had a silvery sheen from the failed bearings. Discovered the nylon detent roller has seized on its shaft and had a flat worn into it..

IMG_5276.jpg

Now cleaned and rebuilt, waiting to go back in..

IMG_5277.jpeg

Started work on the output shaft. Pics to follow
 

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Stirlingmoz said:
Still trying to source a smooth gearbox case to rebuild this into, but just received a shifter mechanism refurb kit from Motobins.

A good kit in my view as it contains all the springs, clips needed for a rebuild, plus a bearing to replace the nylon detent roller.

View attachment 544855

Definitely worth stripping and cleaning as the oil had a silvery sheen from the failed bearings. Discovered the nylon detent roller has seized on its shaft and had a flat worn into it..

View attachment 544856

Now cleaned and rebuilt, waiting to go back in..

View attachment 544857

Started work on the output shaft. Pics to follow
Click to expand...
With those steel ball bearings it will CLACK Like feck on gear changes, thats why BM used Nylons bushes!

Used them once Never again !!
 
DrFarkoff said:
With those steel ball bearings it will CLACK Like feck on gear changes, thats why BM used Nylons bushes!

Used them once Never again !!
Click to expand...

You are likely right but this will eventually be bolted up to a 50 year R60/5 engine with an R90/6 top end and a rather vestigial exhaust system.

Having rebuilt it from the crank up, I’ve spent a lot of time on this engine ensuring everything is adjusted correctly and in balance, but I still wouldn’t describe it as mechanically quiet.

There’s a lot of hardware whizzing around in those cases and one more click will just add to the character.
 
So a few phone calls have yielded a smooth gearbox case and a monolever flywheel.

Spent this morning cleaning up the case..

IMG_5285.jpeg

Got a good start point now.

Off to my sons later to use his press.
 
The gearbox is now partially assembled.

All the gears select - always a good start and everything turns and moves smoothly.

I’m not 100% happy with the neutral switch.

It works from an electrical perspective but the black plastic part moves in the metal body.

Because this is going onto a /5 engine - they are all but impossible to change in situ once the gearbox is fitted.

I’m not taking any chances that it’s going to leak and I’m going to replace it.

Also waiting for a case gasket so I can begin the measuring to work out the shimming.


IMG_5312.jpeg
 
Hi
when my gearbox was rebuilt for me it got a steel ball bearings to replace BM Nylon bush. I never noticed a CLACK although I didnt ride it much cos I got sick. I was told it makes the change smoother, but the Nylon that came out did have a flat on it.

George
 
All my bikes have the metal bearing replacement (comes with the shifter service kit) and none of them clack. Must be irritating.
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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