Gear teeth

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I am in the process of stripping down the gearbox - original intention just to change the layshaft bearing, but made the mistake of looking at the gears.

Many of the teeth have either dull patches across an area near the root, or else slightly irregular lines across which look horribly like the beginnings of fatigue cracks.

Is this as bad as it looks? - replacing all that lot will be £££ :shock:

Or perhaps replace the sleeve gear now & the rest can be done with the box in the bike as the teeth come off? :lol: Anyone got experience of this?
ta
Chris
 
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I had a similar experience. Don't skimp on replacing gears. Something could break, which is a safety issue. Spend the money and have a gearbox that you won't have to worry about for many years. If some of your gears look in bad nick, then it's likely your box has had a long and maybe hard life. Replace any bush that is worn past service limits, and if the ball races are rough, replace them as well. It is critical that you replace not just the drive side layshaft ball race (with roller or special racing ball, I presume), but also have a very close look at the kickstart spindle and its supporting steel bushes in the inner and outer covers. The layshaft runs in a bush in the spindle itself. I took my box down to replace the bush in first gear layshaft (which had started to come out and had partially broken up). I ended up replacing 2nd and 3rd gears as pairs, the kickstart spindle and bushes, most of the other plain bushes and the two mainshaft ball races.
 
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Chris, pictures of your gears might be helpful as it's difficult to judge wear from words. As Dave says, gearboxes are a safety issue but I don't believe that the need for replacement is always clear-cut.

Fourth gear is the most used gear in the box and there is then no loading on the teeth as the sleeve gear is simply dogged to the mainshaft.

In my experience, Commando boxes will often show signs of what I have seen referred to as "spalling" (the same term as they use for flaking of brick-work). This process seems to begin quite quickly but the wear rate stabilises. I have rebuilt several boxes with all new components only to find them looking the same as the old ones after 5000 miles and I'm a bit more pragmatic about it now. I have also had a new 2nd gear pinnion lose a tooth after 1500 miles. (It was sold to me as genuine by a dealer I trusted but Shenstone as it then was denied it was one of theirs).

If you do decide to replace, RGM's own gears are very competitively priced and the finish is much better than the rather crudely cut 'genuine' gears that I have bought. It seems to me that they can do little else than wear each other out before they bed in. I've known several people use the RGM with closer ratio intermediates for racing and have not heard of any problems.
 
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In my experience, Commando boxes will often show signs of what I have seen referred to as "spalling" (the same term as they use for flaking of brick-work). This process seems to begin quite quickly but the wear rate stabilises. I have rebuilt several boxes with all new components only to find them looking the same as the old ones after 5000 miles

I think the above sums up the poor Norton gearbox quite well. The unit was originally designed to serve a 500cc engine, so it's a bit over stressed in the 750 and 850cc engines.

Jason
 
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What you see in the pictures you've posted is fairly typical of Norton gearboxes. You can clearly see the spalling on the gear teeth that 79X100 was talking about; there's no way around it.

Jason
 
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The newness has definitely worn off mainshaft second in the Old Britts pictures. It could do with replacing even if only to keep whining to a minimum. That said, I don't think that it's about to break and you have to consider your annual mileage and type of useage. If you potter a couple of thousand miles a year and don't wring its neck through the intermediates, it could go on for a long time.

If you're not intending to refurbish the bike as "better than new" then it would probably be prudent to check all the bushings / replace the bearings (these can fail quite quickly) and then change the gearbox oil at regular intervals. Even without a magnetic drain plug (you'd need a strong constitution for one of those) you should be able to see if there is an increase in metallic particles between changes.

All things considered, these boxes don't do badly considering that they are basically a cheapened-down version of the pre-war boxes (which has rollers in the sleeve gear but were grease-filled and had no drain plug).

I would say that the change is better than a 1970s Honda and at least the dogs rarely wear.
 
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Howdy ,

Food for thought...
I broke a tooth of third gear and the price of replacing 3rd gear set made it worth while buying a close ratio set which come with the new bushes fitted.
Also makes the bike sweeter.

Cheers
Baldrick
 
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Finally sorted a picture:
Gear teeth


Still considering the options!
Chris
 
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Hi 70 x 100

I am using the RGM close ratio 4 speed.

First gear is supposed to be the type they used on the Manx at Daytona.

The final ratio is still 1.1

Cheers
 
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F_Magna

Do you know how many miles are on the gearbox? Again, the spalling you see on the face of the teeth is fairly typical, even for low mileage components.

Jason
 
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Thanks for all the good info!

The odometer says 17,000, but that's absolutely no guarantee - the rest of the bike indicates more like 117,000.

the number on the gearbox case says 202729, the fame No is 150266

Sounds like an expensive conversation with RGM next week! :shock:
chris
 

Jed

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While consensus is to replace gears in pairs it seems a shame to dispose of 2 perfectly good cogs
First and second on the lay shaft look to have very littte wear while the main gears casing are both noticeably worn
The box appears to have had attention in the not too distant past (maybe the layshaft gears were replaced then along with other components) so I wonder what would be likely to happen if only the main cogs were replaced.
Would it just be noise, would meshing be the problem or would teeth break?

Also I am confused about the layshaft bearing. The one removed is stamped PORTUGAL FAG 6203 which is not exactly the same as the one LAB recommends but looks like it could have been installed at the same time as other bits. Is this the bearing that came with the bike and needs to be replaced?

Comments etc welcome

Gear teeth


Regards

Jed
 
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I rebuilt my gearbox two years ago; the gears looked about the same as your pics. I can't say that it wouldn't be better to install new gears but I'm pretty hard on the bike as far as accelerating/shifting (after all, it was the first bike labeled a "Superbike" and I try to ensure it supports that reputation). There has been no noise or any sign of wear (metal) when the oil is changed. IMO, it's just "the way they are." Again, I wouldn't argue with someone who says you should replace the gears but I think that unless you are going to race it, the gears will be fine for as long as you care to own/ride it.
 

L.A.B.

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Jed said:
Also I am confused about the layshaft bearing. The one removed is stamped PORTUGAL FAG 6203 which is not exactly the same as the one LAB recommends but looks like it could have been installed at the same time as other bits.

It appears to be the standard brass-cage Portuguese-made bearing which should be replaced with either the NJ roller (or 6203TB ball bearing - usually Portuguese made).

Jed said:
Is this the bearing that came with the bike and needs to be replaced?

It's certainly the original type, but it may not be the original bearing.
 
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