Swapping Chaincases

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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spookefoote1956
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Swapping Chaincases

Post by spookefoote1956 »

Ignoring the fact that my Model 18 bitsa has a dynamo; would these crankcases fit on my heavyweight single?

https://www.ebay.co.uk/itm/255862249122 ... R_SXsMCuYQ
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clive
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Re: Swapping Chaincases

Post by clive »

The inner primary chaincase for a twin has a different size hole and bolt spacing at the point of attachment to the crankcase from the inner for a single I believe. If you got round that and wanted to retain the dynamo you would need to adapt both the inner and outer.
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spookefoote1956
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Re: Swapping Chaincases

Post by spookefoote1956 »

Cheers Clive
Hail Joe Lucas ............ Prince of Darkness!
All my bikes are original........ to me!
"Creativity is your intelligence having fun" Albert Einstein
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spookefoote1956
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Re: Swapping Chaincases

Post by spookefoote1956 »

Thanks Clive. Would there be enough room at the front dome for the crank sprockets and engine shock absorber spring? The holes could be altered for mounting. The dynamo would be going as it would be used for an electric start conversion.
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All my bikes are original........ to me!
"Creativity is your intelligence having fun" Albert Einstein
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Duncan
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Re: Swapping Chaincases

Post by Duncan »

spookefoote1956 wrote: Tue Jan 03, 2023 10:20 am Thanks Clive. Would there be enough room at the front dome for the crank sprockets and engine shock absorber spring? The holes could be altered for mounting. The dynamo would be going as it would be used for an electric start conversion.
Hi Chris, I would without checking say not because the 1957 twins that had the AMC gearbox and lost the front shock absorber had a one year only shallow dome in the pressed steel cases.
I have seen modified cases at autojumbles where a piece of short alloy tube has been used to extend the shallow dome in alloy cases to use a shock absorber crank (these are often cheaper as they are not often wanted for by the book restorations), beware though these cases can distort when welded.
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clive
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Re: Swapping Chaincases

Post by clive »

My 58 G11CS has the shallow dome and has only a single line sprocket and no shock absorber spring. I don't think there would be room for the two line sprocket of the single along with the shock absorber. Incidentally the twin hole at the front of the inner is bigger than the single so adapting the screw holes would be difficult and involve welding. I think you would be better looking for a single primary chaincase inner with the cover for the later alternator. I think there may be room for the double sprocket and spring etc in that. Or if not an easier modification.
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Re: Swapping Chaincases

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Re: Swapping Chaincases

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Re: Swapping Chaincases

Post by Joker_Bones »

Couple of pics... Alloy inner case fitted to a single with a crankshaft axle for a shock absorber and a dynamo sprocket.
Note how tight the dynamo sprocket is to the inner case, would not get a chain on it.
Modified centre mounting.
You need an alternator type outer cover to clear the axle/shock absorber
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Re: Swapping Chaincases

Post by clive »

Joker bones I am confused. Are you are driving the clutch from the dynamo sprocket? The chain size is different.
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