Gearbox spotter's guide?

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rcousine
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Gearbox spotter's guide?

Post by rcousine »

I need to buy a new case for an AMC gearbox (1958 AJS 18CS), thanks to a damaged mounting lug.

eBay provides, but some of the vendors aren't sure if they're selling Burman or AMC cases. Is there an easy way to tell from photos?

From my research, it looks like the Burmans consistently have mount lugs that are cylindrical, with cast-in supports leading to the case. The AMCs have ears that smoothly integrate into the case (the mount has a triangular profile) and one of the AMC mounts will have a hole cast into it.

Is this a reliable indicator for such things?

While I have you, two other questions:
-at least one vendor is selling a case with a mount that has been machined down to be 82 mm wide. Is this normal, is it presumably done to re-fit to a different bike, and is it safely correctable with a spacer?
-anything I can look for or should look for in assessing these cases? Is there a known weak spot where they crack?

(My current transmission is intact and seems to work fine, but part of the front mount was destroyed, probably by some motocross activity back in the day. I'll be transplanting the guts and outer covers into this new case)
1958 AJS 18 CS (a work in regress)
Ongoing rebuild photos: https://www.icloud.com/sharedalbum/#B16GWZuqDGvT59n
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dave16mct
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Re: Gearbox spotter's guide?

Post by dave16mct »

If you're looking at the rear part (main) of the shell, there will be 5/16" studs protruding which hold the inner cover. Burman covers are held with 1/4" whitworth screws. Also the AMC box outer has an oval inspection plate held on with 2 2BA screws. The Burman inspection is round with a large screwdriver slot and just screws on. Be carefull not to buy an AMC case from a Norton. Also this another way to identify the box, Matchless and AJS serial numbers start with an 'M' Norton starts with an 'N' (the lugs are in a different place) Burman numbers usually start with 'GB' More about numbers here:

http://archives.jampot.dk/technical/Transmission/

Cheers Dave.
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thornebt
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Re: Gearbox spotter's guide?

Post by thornebt »

As far as identifying whether it's AMC or Burman I think it's as simple as the AMC gearbox has an oil filler cover with two screws fixing it and the Burman box has a large slot in it. Cheers. Bruce.
dodger
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Re: Gearbox spotter's guide?

Post by dodger »

The usual reason for reducing the mounts on a AMC gearbox is to fit it into a norton featherbed frame to create a Triton.
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Peter Morris
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Re: Gearbox spotter's guide?

Post by Peter Morris »

AMC Gearbox
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Peter Morris
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Re: Gearbox spotter's guide?

Post by Peter Morris »

Burman Gearbox
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robcurrie
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Re: Gearbox spotter's guide?

Post by robcurrie »

Peter's photo of the AMC gearbox is a bad example, it is the Norton version. The AJS/Matchless version has a cutout in the top mounting for the adjuster.

Rob C
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Re: Gearbox spotter's guide?

Post by SPRIDDLER »

As well as the Burman GB 'box in Peter's photo there's also the Burman CP 'box fitted to AJS and Matchless bikes and which preceded the Burman GB type up to around 1950 'ish.
This one is from a 1947 Ajay Model 18............
Burman CP Gearbox and drive sprocket (332x480).jpg
100_1559 (480x360).jpg
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'There is a tide in the affairs of men
Which taken at the flood............'
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sjr
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Re: Gearbox spotter's guide?

Post by sjr »

rcousine wrote:I need to buy a new case for an AMC gearbox (1958 AJS 18CS), thanks to a damaged mounting lug.

eBay provides, but some of the vendors aren't sure if they're selling Burman or AMC cases. Is there an easy way to tell from photos?

From my research, it looks like the Burmans consistently have mount lugs that are cylindrical, with cast-in supports leading to the case. The AMCs have ears that smoothly integrate into the case (the mount has a triangular profile) and one of the AMC mounts will have a hole cast into it.

Is this a reliable indicator for such things?

While I have you, two other questions:
-at least one vendor is selling a case with a mount that has been machined down to be 82 mm wide. Is this normal, is it presumably done to re-fit to a different bike, and is it safely correctable with a spacer?
-anything I can look for or should look for in assessing these cases? Is there a known weak spot where they crack?

(My current transmission is intact and seems to work fine, but part of the front mount was destroyed, probably by some motocross activity back in the day. I'll be transplanting the guts and outer covers into this new case)
I have a genuine AMC case which is surplus to requirements. Please send me a PM if interested. Happy to send you some photos.
Regards
Steve
rcousine
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Re: Gearbox spotter's guide?

Post by rcousine »

robcurrie wrote:Peter's photo of the AMC gearbox is a bad example, it is the Norton version. The AJS/Matchless version has a cutout in the top mounting for the adjuster.

Rob C
Ah! Is that cutout in the top mount a decisive indicator it's an AJS/Matchless box?
1958 AJS 18 CS (a work in regress)
Ongoing rebuild photos: https://www.icloud.com/sharedalbum/#B16GWZuqDGvT59n
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