Gear Box Gears

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Stephen Hill

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I have opened up several Norton gear boxes, and each time am disappointed to find a number of pitted teeth, usually on the drive side of the mainshaft gears, and on the 4th gear (the little gear) on the mainshaft. The pitting will be on one gear,but not on the mating gear.

I have seen a number of theories about why this happens: the gearbox was designed for 30 hp, not 70 hp, too narrow teeth, condensation, low levels of lubrication, infrequent oil changes, wrong oil, and bad mettalurgy/inadequate hardening.

Question #1 I have heard that you should replace each worn gear and its mate. In my case each gear is worn and not its mate, and I have four worn gears, so I guess I should replace 8 gears. This seems over the top. How important do you think it is to replace the gears in pairs?

Question #2 I have taken a sharp file to the teeth and had no difficulty removing material to produce a smooth face, down to the level of the pitting. I was removing the proud unpitted material, making me thing the tooth is too soft. Is this a reasonable conclusion?

Question #3 Given how soft the gears are, and that I can reshape the pitted ones with a file, I could probably reshape or at least smooth the surface of some of the gears. Has anyone ever dressed the gears, superficially or more, and then used them with any success?

Question #4 What if you just throw the pitted gears back in and just use them? Note I am talking about pitted teeth where the structure or mass of the tooth is pretty much intact.

Stephen Hill
Victoria, Bc
 
Question #1 I have heard that you should replace each worn gear and its mate. In my case each gear is worn and not its mate, and I have four worn gears, so I guess I should replace 8 gears. This seems over the top. How important do you think it is to replace the gears in pairs?


Yes its important but have never followed it and never had a problem :D .

On the rest the gears are case hardened, so if you take any more off you risk the soft core being exposed, the pitting will act as an oil reserve and I would leave it as is if the gear is not worn overall.
 
I think the gears have hardened surfaces (?), so if the pitting has breached that and/or you file it off, I would think the gear faces will subsequently wear at an accelerated rate.

I found some pitting on a couple of my gears also (don't remember which ones). I bought a used box off eBay and cannibalized the best parts from both boxes to produce one good box.
 
Pitting is found most frequently on first main and second main, the two smallest gears in the box. The lay gears of these two are among the two largest gears in the box, and, in my experience, are rarely pitted. Old Britts shows examples of pitted gears to use as a comparison. Since the larger lay gears do not wear as much (the strtess is distributed over more teeth), I only replace the pitted main gears. This argument may not apply to 3rd and 4th, as the main and lay gears are closer in size, but these gears normally suffer less stress in riding. In my case, after 24,000 miles, only the first two main gears showed pitting, and I replaced them both.

The use of Redline Shockproof Heavy in the gearbox will reduce future wear.
 
If the gearbox is still driving you forward and not jumping out what the heck. The gears in my Mk3 have done 200k and yes they're pitted but they change like silk and are pretty quiet too. :D

Don't fix it if it aint broke .

Cash
 
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