Norton Gearbox Fitted to Comet

Michael Vane-Hunt

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DSC05455.JPG
Here is how John mounted a Norton AMC gearbox on my recent Comet project. He removed the adjusting lug from a sacrificial BAP box and welded it to the Norton box and added a pivot mounting lug on the top. This way the original mounting system is used. There are some tight fits with the valve lifter and clutch cables but it all seems to work. Now to see if this post works.
 

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highbury731

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. Norton boxes have a prefix of "N" or "NA." Matchless boxes have a prefix of "M" or "MA." I believe the single prefixes were used post 1957 and the "A" was added to both after AMC bought Norton around 1962.

David

AMC actually bought Norton around 1954 (blame the featherbed), but later, moved Norton production to Plumstead around 1962. The AMC box was introduced in 1956, the change to 'A' suffix on the gearbox probably refers to the altered ratios brought in in 1960.

Starting from the 'horizontal' gearbox which actually shared its gearcluster with the 'vertical' box and even the pre-War 'doll's head' box, the early AMC had a closer first gear and much lower third. For the 'NA' box used a fractionally closer sleeve pair, a fractionally wider third pair than the pre-AMC giving the same 1.21:1 ratio as 'horizontal' and earlier, and closer second and first.

If you know your Norton boxes and tooth numbers, you can select your own gear cluster. But be careful - the AMC box needs a shoulder on the mainshaft first gear, and third main does not have clearance for the bronze thrust washer between third and sleeve gear on the earlier boxes, so engagement dogs do not line up if you mix box types with the third and fourth mainshaft gears. Confused?

Well, you could get the same result as an 'NA' box by taking a pre-AMC box and adding a late Commando second and AMC first.
 

vibrac

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RGM do a lot of Norton stuff including a couple of close ratio adaptations but it is a bit of a jungle
 

nkt267

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If you need the gearbox mod print out..right click the the attachment that Davidd has posted above--select 'open in new window' and the attachment should download--open the download and right click in an unprinted area, select 'save as' and you can save it to your computer...think i have that right..John
 

nkt267

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you can save the individual pictures that are also posted.Right click each pic and open in a new tab,you can then save them with the instructions..john
 

davidd

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John,

Thank you for the instructions. I was not certain how clear it was to all of the participants that all of the information on the new forum is easily downloaded. In fact, I started the post just so everyone would have access to the information and others would join in with valuable information, which was done. I think this is the best improvement of the new forum. People have asked me for years about this information and now that the files and photos stay with the post it should be a great resource for anyone contemplating this project.

David
 
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