Previous owners...

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Pharisee
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Previous owners...

Post by Pharisee »

Some of you may be aware of my M18S "Bess" as it, and the problems a previous owner had caused me, were featured in the 'Jampot' a few months ago. Well I've just found another one (problem, that is). When I had the engine and gearbox out to repair the oil pump, I failed to notice that the cover plates on the end of the swinging arm pivot had been put back on the wrong side. Earlier today I changed all the oils and filled the oil can with Castrol D140 to top up/refill the swinging arm reservoir. It was only then that I noticed that the filler screw was hidden behind the primary chain case and totally inaccessible.
Don't you just hate it when that happens?
As it happens, I already had plans to strip off the primary drive. I recently carried out the revised cam timing and shorter inlet pushrod rocker modifications that were discussed in an earlier thread and I'm well impressed with the way Bess is running. She's pulling strongly up to 75mph but at that speed the engine was sounding very 'busy' indeed so I didn't push it any further. As first gear is quite low; pulling away in second is not difficult, I thought I'd change the gearbox sprocket for a larger one. Currently, there's 17 tooth sprocket fitted but I'm getting increasingly confused about what is 'standard'. The '55 parts list says it's part number G-31-1 at 16 teeth. F Neils manual says that 21 teeth is the 'standard' for '45 to '56 M18S and the '57 model had 22 teeth.
Could someone enlighten me as to what sprocket is normally used on a touring 500... please?
Thanks
John

[EDIT....] I should perhaps add that it has an 18 tooth engine sprocket fitted.
I'm from the Fens.... Gimme six.
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ajscomboman
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Re: Previous owners...

Post by ajscomboman »

16 tooth is standard 17 is the upgrade. The other sprockets you mention are engine sprockets 21 up to 57 and the 22 onwards. 18 tooth engine is for a 350
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Pharisee
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Re: Previous owners...

Post by Pharisee »

ajscomboman wrote:16 tooth is standard 17 is the upgrade. The other sprockets you mention are engine sprockets 21 up to 57 and the 22 onwards. 18 tooth engine is for a 350
Yes... I realised that I'd got confused with the engine sprockets.

So... I have a 18/21 tooth engine/dynamo sprocket driving a 40 tooth Burman clutch drum and a 17 tooth gearbox sprocket driving a 42 tooth rear wheel sprocket.
That gives and overall top gear of (40/18 x 42/17) 5.49:1 which is lower than the standard (40/21 x 42/16) 5.00:1 and probably accounts for the engine sounding 'busy' at 70mph.

A new 21/21 engine/dynamo sprocket is a bit expensive, even if I could find a new one (AMOC Spares out of stock) so I think the best alternative would be to fit either an 18T (5.18:1) or a 19T (4.91:1) gearbox sprocket. Both seem to be available at a reasonable price.
I'm from the Fens.... Gimme six.
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