Model 20B Crankshaft ID

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

Postby 54 Model 20B » Mon Aug 06, 2018 7:09 pm

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

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Re: Model 20B Crankshaft ID

Postby G15 Roy » Mon Aug 06, 2018 7:53 pm

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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Re: Model 20B Crankshaft ID

Postby Duncan » Mon Aug 06, 2018 9:16 pm

Possibly a different balance factor due to the larger pistons hence the different part number?

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Re: Model 20B Crankshaft ID

Postby 54 Model 20B » Wed Aug 08, 2018 9:34 pm

Thanks for the input. I believe it is balanced differently after lots of research. Thank you for the replies.

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Re: Model 20B Crankshaft ID

Postby ajscomboman » Thu Aug 09, 2018 7:53 am

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

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Re: Model 20B Crankshaft ID

Postby 54 Model 20B » Sat Aug 25, 2018 9:19 pm

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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Re: Model 20B Crankshaft ID

Postby 54 Model 20B » Sat Aug 25, 2018 9:24 pm

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

Thanks

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Re: Model 20B Crankshaft ID

Postby SPRIDDLER » Sat Aug 25, 2018 9:58 pm

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 10:02 pm, edited 1 time in total.
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Re: Model 20B Crankshaft ID

Postby 54 Model 20B » Sat Aug 25, 2018 10:00 pm

Thanks you!

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Re: Model 20B Crankshaft ID

Postby Peter Morris » Sun Aug 26, 2018 6:08 pm

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


:rofl: :rofl:

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