G80s box of bits

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Tommy-T
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Location: Devon United Kingdom

G80s box of bits

Post by Tommy-T »

Good morning, just purchased a 1957 frame & wheels, a nearly complete 55 engine, a couple of cylinders, 2 magnetos plus other bits and bobs. I also have a tank with side panels and knee pads for a AJS which doesn't fit. I'm missing a correct tank and a carb, plus lots more as I get into it I'm sure! A couple of questions, the washer between the two main bearings was destroyed, should be there? This is the stepped housing 1955 casing. The carb for mine should be a monobloc 389.1 5/32, do need to stick rigidly to this or are there other alternatives to achieve good results? Thank-you.
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dave16mct
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Re: G80s box of bits

Post by dave16mct »

Yes the washer should be there between the bearings. I prefer the 389 monobloc but there are alternatives. Some fit a concentric, I've also got a friend who fitted an Amal Mk11 to his '57 18S. I think you're better off with the 389. It sounds like you need to join the club.
Dave.
Tommy-T
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Re: G80s box of bits

Post by Tommy-T »

Thanks for the advice Dave, I did read a post regarding the washers, whether to fit in the 1955 casing, now I have had a better look, there were three washers and a copper washer on the shaft, up against the crank! Probably why the washer between the bearings was shot. another question, I have a Burman box and a AMC box also in my box of goodies. I read that the newer box was quite highly praised, any thoughts on which one to put my time to ?assuming the internals are ok.
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Pharisee
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Re: G80s box of bits

Post by Pharisee »

Tommy-T wrote: Wed May 05, 2021 8:03 pm another question, I have a Burman box and a AMC box also in my box of goodies. I read that the newer box was quite highly praised, any thoughts on which one to put my time to ?assuming the internals are ok.
It depends a bit on whether you have a Burman or an AMC clutch. Use the gearbox that suits the clutch. You can't fit an AMC clutch directly to a Burman gearbox. You will need to make up a 3/8" thick spacer on the Burman mainshaft to bring the clutch sprocket in line with the engine sprocket. That doesn't leave very much thread for the retaining nut. Both are good boxes. The AMC is smoother on the gearchange. The Burman box need a slower, more deliberate action on the change lever.
I fitted an AMC clutch and gearbox in my '54 G3/LS which had Burman units originally.. There were no problems with the primary chain alignment but I did have to remove a little metal from the right hand engine plate to allow the gearbox to move over its full adjustment arc.
John
I'm from the Fens.... Gimme six.
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dave16mct
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Re: G80s box of bits

Post by dave16mct »

I agree with Pharisee. I'd fit the AMC box and clutch given the choice and you've a '57 frame which would have had that originally.
Dave.
Tommy-T
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Re: G80s box of bits

Post by Tommy-T »

Thanks for the advice, there are two clutches in the box, will drag them out for a closer inspection, wasn't aware they may be different makes. Engine is nearly completed, a piece of box section steel, shaped and drilled made a useful valve spring tool and my purchase of 40 scotchbrite pads for a dremel has to be the best buy ever! Six quid.
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Pharisee
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Re: G80s box of bits

Post by Pharisee »

The Burman clutch has 5 springs, no integral shock absorber (the shock absorber is on the crankshaft) and has 40 teeth on the sprocket. The AMC clutch has 3 springs, an integral segmented rubber shock absorber and 42 teeth on the sprocket.

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Pharisee
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Re: G80s box of bits

Post by Pharisee »

If you choose to use the AMC clutch and gearbox, be aware that the extra two teeth on the AMC clutch basket will lower the overall top gear ratio a little. The '55 G80 engine would have had a 21 tooth engine sprocket driving a 40 tooth clutch sprocket coupled with a 16 tooth gearbox sprocket driving a 42 tooth rear sprocket/brake drum, giving an overall top gear ratio of 5.00:1. The extra two teeth on the AMC clutch sprocket will lower the overall top gear ratio to 5.25:1. The engine will be revving proportionally higher for any given road speed. Fitting a 17 tooth gearbox sprocket will raise the gearing back to a more acceptable 4.94:1.
John
I'm from the Fens.... Gimme six.
Tommy-T
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Joined: Sun May 02, 2021 11:31 pm
Location: Devon United Kingdom

Re: G80s box of bits

Post by Tommy-T »

Thank you John, very helpful, as a result I can see I have both clutches so will pull them apart along with the respective gearboxes to decide on which to use.
Also I have two mags, one being a Lucas but the other hasn't got any markings other than stamp numbers. Looks like a BTH ? Trying to suss out how to add a photo.
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clive
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Re: G80s box of bits

Post by clive »

Tommy-T wrote: Fri May 07, 2021 11:25 pm Trying to suss out how to add a photo.
Not sure you can as a guest. If you can then when in full editor you will see below the text box "attachments". Click this and you can upload a picture that is up to 3 mb.
clive
if it ain't broke don't fix
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