Twixmas Gearbox

[Stirlingmoz]

I picked up this broken gearbox on eBay earlier this year. It was filthy, stuck in gear and cheap as chips so I thought worthy of a punt.
Had some time twix Christmas and New year to delve into it.



First step was to crack it open. Fortunately it all looked very nice inside.



Got it fully apart and laid out on the bench



Time for cleaning and a closer inspection of what we have

 

[Stirlingmoz]

Here is the gear selector mechanism.



You can just make out the broken spring that resulted in it being stuck in gear. (I manually selected neutral in the photo)

Here is the broken spring and it’s replacement



I used a Motobins kit to refurb the selector mechanism. All the springs and clips required plus it replaces the nylon roller with a small bearing



Horrible job but got the gearbox case into a clean condition that I was happy with

 

[Stirlingmoz]

Time to have a closer look at the gear shafts.

I have learned it’s good practice to change the bearings whist its apart and these are on order.

All the gears look to be in good clean condition.

Here’s the output shaft by way of example



The output shaft transpired to be the type without a circlip



Will try and locate a shaft with a circlip groove and swap all the gears etc over

 

[Stirlingmoz]

Found an output shaft and miscellaneous gearbox parts.

The difference between an output shaft with a circlip groove and one without. The right side shaft has the groove at the front (top)..



Check out this output shaft 3rd gear that came with it.

Less teeth than my grandad



Something pretty bad befell that gear !

And this is me fighting the large bearing on the end of the old output shaft.



The puller was starting to bow before the gear began to move.

I was able to strip everything off and give the parts a good clean

 

[Da1sycat]

Fair play i wish I had your talent

 

[Oldrat]

Fair play i wish I had your talent

Me too!

Top job

 

[Mad Hatter]

Might be worth checking that shaft is 100% straight before using it, just in case those missing teeth went in between the gear clusters! Great work BTW!

 

[Stirlingmoz]

Thanks guys. As far as I can tell with the tools I have, the new (old) output shaft is straight. There are no witness marks I can see to indicate any of the grooves are damaged. All the gears and washers slid on smoothly so my fingers are firmly crossed

Reassembled the shaft this afternoon with a new rear bearing and temporarily fitted the old front bearing - just to keep it all together.



Here’s the money shot with a circlip fitted to eliminate the risk of the bearing moving along the shaft under load (or is it the shaft pulling out of the bearing under load) Anyhoo - that is a potential problem eliminated now.



Got to wait for our favourite suppliers to re-open so I can order some new bearings etc.

 

[Gelandestrasse]

Did you put the snap-ring behind the circlip? Essential. 23 21 1 235 006 . Part 3:

 

[Stirlingmoz]

Did you put the snap-ring behind the circlip? Essential. 23 21 1 235 006 . Part 3:

View attachment 470354

I did and replaced the circlips as a precaution

Got a little further with it today



Checked that all gears select.

Time to measure up for the shimming

 

[Stirlingmoz]

It took me a while to measure (re-measure), and calculate (re-calculate) the shimming, but I got there in the end.

Here it is back together.



Still turns and all the gears still select.

Only oil seals and the humongous torque on the drive flange to go.

Even though the gearbox itself was a snip, all the parts to refurb one, soon add up.

 

[Mad Hatter]

Really great job you've done on that, you made it look easy!

 

[Gee-]

Would you classify yourself a fitter, mechanic, or an engineer?........I would class you as a bike fixer God!

Well impressed with your knowledge and ability, excellent images to show just what was involved. TY.

 

[Stirlingmoz]

Just a hobbyist. I have a dull day job and garage time helps keep me sane.

But..I may have my first commission build.

Purely through word of mouth, I’ve been asked if I’d build an airhead based bobber for a guy.

Not my taste at all, but I’m up for the crack.

If it comes off, I’ll start a thread

 

[Gee-]

Will be looking forward to that, if your last post was anything to go by......very interesting.

I was content with my previous job "Hgv Trucker" but wished I had more knowledge and know how to do more on bikes.
Like yourself, not really into Bobber's, but any build always fascinates me, and wait with interest regarding your future threads.

 

[Bubb]

Just a hobbyist. I have a dull day job and garage time helps keep me sane.

But..I may have my first commission build.

Purely through word of mouth, I’ve been asked if I’d build an airhead based bobber for a guy.

Not my taste at all, but I’m up for the crack.

If it comes off, I’ll start a thread

Hope you retain a “veto” so the thing has at least some taste…..
I’m sure some of the ideas that some people want come under the umbrella of “ what the feck were they thinking”….. and if you retain a veto you might keep the build out of that genre….ive seen your street scrambler thing and that’s fine imho…

Start a separate thread on the build please Pete.

 

[Posh Pete]

Is it not possible to machine a groove on the shaft for the circlip?

 

[timeandtide]

Really great job you've done on that, you made it look easy!

Didn’t he!

 

[Stirlingmoz]

Is it not possible to machine a groove on the shaft for the circlip?

I believe it is possible by an engineering shop.

I really should have taken some measurements as I now have 2 output shafts that could be potentially modified.

 

[mikeyboy]

I believe it is possible by an engineering shop.

I really should have taken some measurements as I now have 2 output shafts that could be potentially modified.

Pretty straightforward,get a new front bearing,
Press it on ,measure to front of bearing,remove bearing and cut the recess to the same width as circlip.
We retro fit circlips on any box not already fitted with one.