Gearbox gear replacement?

Hi all

Resto of 1968 commando coming along nicely. Spending more than I hoped to, but after reading posts here I should have known better. Anyway.... Gearbox!!!

Opened it up to "just refresh it" seals and bearings and all was going well... Kickstart Pawl looks brand new. Great.
Oil looks clean, no metal. Great. Not much in there?

1st gear lay shaft gear, perfect.
1st gear main shaft gear..... Crap. Then it starts.

2nd gear lay shaft gear perfect.
2nd gear main shaft gear... Crap.

Both 3rd gears good

4th both crap.

So the question is (finally) what are opinions on just replacing bad gears. I know the manual says to replace in sets but that's 2 expensive gears that are in good condition. Has anyone put a used gear with a new gear?
Is there a way I could lap the gears together to bed them in before assembly?

The bike is going to be for road and regularly ridden, probably 2 or 3 times a week. So I want it to be right. But I don't want to spend $200 if I don't have to.

Thanks as always,
D

Don't worry about spending $200 for new gears. If the gearbox blows up you will be wishing you had spent the money upfront. Go with the later real deal Andover Norton 2nd gear set. they make downshifts much better. I (and I suppose others) have a pile of used gears, but it is the same deal, if that transmission blows up and busts the case you are going to be very sad. There is a reason that there are not a lot of matching numbers when it comes to transmissions in the early bikes.

Greg

Dean said:

Hi all

Resto of 1968 commando coming along nicely. Spending more than I hoped to, but after reading posts here I should have known better. Anyway.... Gearbox!!!

Opened it up to "just refresh it" seals and bearings and all was going well... Kickstart Pawl looks brand new. Great.
Oil looks clean, no metal. Great. Not much in there?

1st gear lay shaft gear, perfect.
1st gear main shaft gear..... Crap. Then it starts.

2nd gear lay shaft gear perfect.
2nd gear main shaft gear... Crap.

Both 3rd gears good

4th both crap.So the question is (finally) what are opinions on just replacing bad gears. I know the manual says to replace in sets but that's 2 expensive gears that are in good condition. Has anyone put a used gear with a new gear?
Is there a way I could lap the gears together to bed them in before assembly?

The bike is going to be for road and regularly ridden, probably 2 or 3 times a week. So I want it to be right. But I don't want to spend $200 if I don't have to.

Thanks as always,
D

Click to expand...

Gidday Dean. Just refering to your post mate. it would be very good if you could get some photos up here please. especially the sides or flanks of the tooth in good close up if at all possible.

Showing pits and tooth damage would be real good too.

A picture tells a thousand words, or so I am told.
some good photos would very much help differentiate between what is "good" and "bad" of your set.

I cant resist this. A free plug. To those having difficulties posting photos, VIP membership is a revelation.
best wishes to all bradley

Hi there, I MADE THE MISTAKE of not replacing the 3rd gears. I am faced with going to the nz rally with the noisey 3rd but that's just tough, as I don't have the time to fix it.
When I rebuilt the box I did all the right things and was advised the new gears were not as good as the old gear s and would go through the hardening very quickly. I replaced all the bearings and the bushes that were worn, and the third gear was noiser after the rebuild than before. Pissed me off. I now ride mostly in top gear, and used third as a transition where I have to. Itys a shit but ya gotta do what ya gotta do.
My recommendation is always replace the gears as matched sets. You can always save the better gears for next time. It will cost a lot but it will be good. That's what we were taught in the trade. If you mismatch the gears, you can end up with noise you don't want to hear because of different wear patterns, even if the gears look ok.
Dereck

I had similar dilemma but in the end i replaced gears as pairs an mainshaft that was ridged in sleeve gear area. The box did work fine but the knowledge that it was slowly killing itself an one day would fail made me do it. If like me you have no plans to sell the bike an tend to keep things for many many years then it was case of if i fix it now i won't have to fix it in the future when it will most definitely cost more anyway.

The other point to think on is if the box fails in a big way as even in good condition its somewhat over stressed then it could lock up the rear wheel in the worst case scenario. Pulling in the clutch won't help and you an your nice bike may end up on the floor which will hurt you it and your bank account more than price of few extra parts now.

Gidday Bradley
So nice to hear an Aussie accent again. I'm an Aussie living in Abu Dhabi. From Wello point in brisbane.

Anyway am stuck in Narita Japan at the moment for work so don't have access to the gears to get pics so pinched some off a web site. You have probably seen these if you have done a g/box O/haul.

My gears that are "crap" look exactly like the ones in the pics. The ones that are good look like they brand new??? No pitting or damage at all on the teeth or dogs. How does a gear running against a pitted one not get damaged???

I digress. (Again)
Sort of knew this was the answer I was going to get... Why is it always the answer that cost $$$$.
After adding up what I definatly need for the box... Another $200 is small potatoes.
May as well change them for piece of mind.
THANKS GUYS

+1 VIP. small cost for much easier posting of pics. And a small price to pay to keep the most informative Norton commando forum around alive.

FWIW, I replaced a fair number of gears and shafts in my race Nortons back in the day, in both stock and Quaife gearboxes, and always tried to replace anything that looked worn while the gearbox was apart. Several times I replaced only one gear of a pair, if the other one wasn't worn, and never experienced any odd noises or early failures. Replacing both at the same time is probably a good thing, but I never had a problem with not doing so. YMMV

Ken

The advice about only changing gears in pairs was only to preclude the possibility of getting any of the earlier AMC gears into the mix (?).
If you were always purchasing from the same supplier of Commando gears, this wouldn't/shouldn't be an issue...

What might be a concern is that if some of the gears now look new, and some are a bit worn,
then maybe the PO only replaced the REALLY worn gears !

lcrken said:

FWIW, I replaced a fair number of gears and shafts in my race Nortons back in the day, in both stock and Quaife gearboxes, and always tried to replace anything that looked worn while the gearbox was apart. Several times I replaced only one gear of a pair, if the other one wasn't worn, and never experienced any odd noises or early failures. Replacing both at the same time is probably a good thing, but I never had a problem with not doing so. YMMV

Ken

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I have replaced a lot of gears without replacing the mate also. Never had a problem with it. I kind of figured a used gear without damage was "tested tough" Jim

Maybe we should be looking to see if some gears wear, and some don't ?

Well, just from the mechanics of it, I would expect that in a pair of gears the smaller one would wear faster than the larger one. In any given period of time, the smaller one sees more impacts/wipes per tooth than the larger one. Seems reasonable to me, but I don't recall whether that's what I saw in my own experiences.

Ken

that is pretty much the pattern I have seen with 1st and 4th but 2nd and 3rd pair pretty much wear the same.

lcrken said:

Well, just from the mechanics of it, I would expect that in a pair of gears the smaller one would wear faster than the larger one. In any given period of time, the smaller one sees more impacts/wipes per tooth than the larger one. Seems reasonable to me, but I don't recall whether that's what I saw in my own experiences.

Ken

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lcrken said:

Well, just from the mechanics of it, I would expect that in a pair of gears the smaller one would wear faster than the larger one. In any given period of time, the smaller one sees more impacts/wipes per tooth than the larger one. Seems reasonable to me, but I don't recall whether that's what I saw in my own experiences.

Ken

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That makes sense now that I think about it. The worst one was the 1st main while the much larger 1layshft gear is perfect. Would be interesting to hear if anyone has actually had a gearbox "blowup" from a broken gear. I know the lay shaft bearing was a problem due to quality issues and if you dump the clutch and try to "wheelie away" you can break the lay shaft, but have never heard of a broken gear.
Will start a new thread to get some info on g/box blow ups.

Also thanks all. I think I'll just replace the damaged parts.
I used to overhaul aircraft engine gearboxes and we never replaced gear sets. But then I never heard of anyone dumping the clutch in a 737 either
D

Ms Peel broke a few teeth out of both 3rd gear cogs and yes it was from a clutch dump I thought I'd snicked to 2nd to reel back in a Ducati Monster that pulled away form its group for games and I'd waited behind a car so they could see what they'd been trying to catch for miles. We played a few more miles and again for a dozen more till pieces jammed into 4th to get back home on. Kenny Cummmings has broken the Commando TS pinon gear so replaced with stronger/wider Atlas item. My sense of it is the shafts bow and twist which unfailry binds the cog teeth.

The main reason I bought the 6 speed TTI box was to avoid the big clutch dump to heave the bike quickly off the start line in races. If you spin the heavy commando crank to about 4000 RPM and dump the clutch, the loads in the box which has a high first gear must be horrific. Better to spin it to 2000 RPM and ride the clutch out quickly relying on the two low gears for acceleration off the mark ?