Model 20B Crankshaft ID

Information relating to the Matchless G9 or AJS Model 20 500cc twin
54 Model 20B
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Model 20B Crankshaft ID

Post by 54 Model 20B »

Hello,
Does anybody know the difference between the Model 20 and the Model 20B crankshaft? There is a supplemental parts list for the Model 20B bikes. One of the items in the supplemental parts list is the crankshaft, and is a different part# than what is shown in the standard parts list. The crank shaft I pulled out has worn splines in the end and needs replacement. I bought a replacement off eBay, but not sure if it's a Model 20 or 20B. It did come from the USA, so it may be a model 20b. But need more info to ID.

Thanks
G15 Roy
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Re: Model 20B Crankshaft ID

Post by G15 Roy »

I would say the crank is the same, and all to do with the size of the bore from 66mm to 69mm and the skirt on the barrels. Hope this helps. A frame number to the dating service will reveal the model.
Roy
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Duncan
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Re: Model 20B Crankshaft ID

Post by Duncan »

Possibly a different balance factor due to the larger pistons hence the different part number?
54 Model 20B
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Re: Model 20B Crankshaft ID

Post by 54 Model 20B »

Thanks for the input. I believe it is balanced differently after lots of research. Thank you for the replies.
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ajscomboman
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Re: Model 20B Crankshaft ID

Post by ajscomboman »

54 Model 20B wrote:Thanks for the input. I believe it is balanced differently after lots of research. Thank you for the replies.
I'd still purchase a Mod 20/G9 crank and have it all balanced at an engineering workshop to suit. Apart from the balance factor the cranks are identical
54 Model 20B
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Re: Model 20B Crankshaft ID

Post by 54 Model 20B »

hello,

I got the crankshaft pulled out of Model 20B. The previous owner replaced it after it broke and never got it started again, this was 30 years ago. It weighs about 5 1/2 pounds more than the stock Model 20 crankshaft I bought off eBay. I didn't realize that they are different part numbers until after I made the purchase. The ends on the crankshaft I removed from my bike are completely round. The EBay crankshaft ends are triangular. Just want verify if possible that the crankshaft I removed from the bike is a correct replacement for my Model 20B. I am now thinking about having it fixed, the splines need to be repaired. I've seen pictures of both styles of crankshafts online, and they are both listed as Model 20/30. Please see attached pics, thanks for any help.
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54 Model 20B
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Location: United States

Re: Model 20B Crankshaft ID

Post by 54 Model 20B »

Sorry the way the pics came out. Should be able to scroll side to side to see the end plate.

Thanks
SPRIDDLER
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Re: Model 20B Crankshaft ID

Post by SPRIDDLER »

Crankshaft (494x640).jpg
Crankshaft 2 (481x640).jpg
Saves going next door to see the whole thing ;)
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Last edited by SPRIDDLER on Sat Aug 25, 2018 11:02 pm, edited 1 time in total.
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54 Model 20B
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Re: Model 20B Crankshaft ID

Post by 54 Model 20B »

Thanks you!
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Peter Morris
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Re: Model 20B Crankshaft ID

Post by Peter Morris »

SPRIDDLER wrote:
Saves going next door to see the whole thing ;)
:rofl: :rofl:
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