Gear Box Issues

My 1974 Commando 850 locked up my rear wheel yesterday, strongly supspect gear box issues..... Fortunately proceeding slowly, pulling in the clutch did not help. My kick starter level locked to the forward motion of the bike and was found in a most un-natural position.

Trailered it home and found a wonderful bronze glitter in my transmission oil. So it comes apart. Few questions for the experts here:

a) Should I pull the transmission off as a unit, of just dis-assemble as I go leaving it in place? Manual shows it both ways.
b) Andover Norton sells a re-build kit, is this a good quality option?

Thanks!
Marco

Your driveside Layshaft ball bearing is kaput, the cage disintegrated and allowed the balls to descend to the bottom of the bearing and so escape. The balls were then free to jump up and get caught between the gears and lock the gearbox.

Happened to me but the balls got chopped up and the rear wheel did not lock. I could only get 4th gear and rode home through a busy sat afternoon city centre without stopping. My steel clutch plates were blue and still are 30 years later.

I fixed it all with the gearbox in the bike and everything came out except the mainshaft.

You will need more than a rebuild kit, its good but expect to find damaged teeth on the gears from those bearing balls.

The ball bearing is best replaced either with a roller or another ball bearing but with a special cage. The ball bearing means no shimming is needed, roller is cheaper but you will need to shim for endfloat or risk jumping out of first gear on acceleration.

MarcoNC850 said:

My 1974 Commando 850 locked up my rear wheel yesterday, strongly supspect gear box issues..... Fortunately proceeding slowly, pulling in the clutch did not help. My kick starter level locked to the forward motion of the bike and was found in a most un-natural position.

Trailered it home and found a wonderful bronze glitter in my transmission oil. So it comes apart. Few questions for the experts here:

a) Should I pull the transmission off as a unit, of just dis-assemble as I go leaving it in place? Manual shows it both ways.
b) Andover Norton sells a re-build kit, is this a good quality option?

Thanks!
Marco

Click to expand...

Easy fix in-situ

You may find this series of videos useful…

Repair



Rebuild



Not necessarily required, or the same thing, all the time.



INSPECT.


Decide.


Implement.

Appreciate the feedback and the link to the video, I will continue the disassembly and update the thread.

MarcoNC850 said:

Andover Norton sells a re-build kit, is this a good quality option?

Thanks!
Marco

Click to expand...

Yes, good quality, but unless someone asks me to replace all that, I don't use it. I've never found a gearbox that need all those components. More normally a bushing or two, a bad gear or two, a ratchet spring, the bearings, and the gasket/seal kit. Of course, if everyone is right and the ball bearings from your layshaft locked your gearbox, you probably need a main shaft and maybe a layshaft, some gears, and possibly a new shell and that kit doesn't have any of those expensive parts.

Since I rebuild quite a few, I'm always on the lookout for cheap gearboxes. disassemble, clean, inspect, throw away bad and keep the rest for rebuilds.

If you're going to do it, I recommend taking the gearbox out, disassembling, cleaning, inspecting and figuring out what you need. Could be a little, or could be better to buy a used one and combine them.

Whatever you do, do not hammer or jerk the bearings out - heat to about 225F, slam on wood and they will pop out. They drop in if properly heated. Drive or jerk them out and the hole in the aluminum can get to be too big!

cliffa said:

You may find this series of videos useful…

Click to expand...

Surely there must be another rebuild video for grown-ups?

- Knut

concours said:

Easy fix in-situ

Click to expand...

Including bearing removal and re-fitting? I don't think so.

- Knut

mdt-son said:

Surely there must be another rebuild video for grown-ups?

- Knut

Click to expand...

No way in hell I would use an electric or air impact on those recessed straight slot screws! A hammer impact would be fine as it is very unlikely to stripe the head. that's as far as I got! The thought of trying to drill out the stripped screws - wow!

mdt-son said:

Including bearing removal and re-fitting? I don't think so.

- Knut

Click to expand...

And, if doing the bearings or anything that requires removing the main shaft, the primary is already apart so why struggle - just take it out!

Since I have a Minnesota winter coming up and a new set of Isolatics to go in, I am thinking just to remove the engine and gear box as a unit and bring it to a nice and warm basement for the re-build...

MarcoNC850 said:

Appreciate the feedback and the link to the video, I will continue the disassembly and update the thread.

Click to expand...

The shell can be heated with heat gun or torch, this grabs the bearing: https://www.harborfreight.com/slide-hammer-and-bearing-puller-set-5-piece-62601.html

Easy and quick.


Two months of glorious weather remain.....

MarcoNC850 said:

Since I have a Minnesota winter coming up and a new set of Isolatics to go in, I am thinking just to remove the engine and gear box as a unit and bring it to a nice and warm basement for the re-build...

Click to expand...

Don't remind me.

mdt-son said:

Including bearing removal and re-fitting? I don't think so.

- Knut

Click to expand...

Mick Hemmings GB Rebuild DVD from INOC is the gold standard and must have if planning to do it as a first timer.

I did a full rebuild, all seals, bushings, bearing, in frame. Used the deep groove phenolic ball bearing to swap out the Portuguese P.o.S. failure prone layshaft bearing.