Swap Tim Primary for All-Alloy Cases?

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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peterg123
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Swap Tim Primary for All-Alloy Cases?

Post by peterg123 »

Can you use a pair of magneto model alloy chaincases in place of tin ones for a 51-54 model using a Burman B52?
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Duncan
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Re: Swap Tim Primary for All-Alloy Cases?

Post by Duncan »

There would not be room for your engine shock absorber on the end of the crankcase unless you modify them (caution: welding normally distorts them), additionally the cap on the inlet cam needs recessing in (if this is a breather on your model there would be problems) and a support fabricating for the back of the chain case.
peterg123
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Re: Swap Tim Primary for All-Alloy Cases?

Post by peterg123 »

Thanks Duncan but the magneto alloy case was made for the Magnet drives G9's etc and they had engine shock absorbers? I intend to use the alloy cases with a 51 G9 engine?????
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Duncan
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Re: Swap Tim Primary for All-Alloy Cases?

Post by Duncan »

in 1957 AMC clutches were first fitted that have the shock absorber in the clutch and a shorter crankshaft drive shaft axle (no shock absorber on the crankshaft) one year only pressed steel chain case was used for this year with a reduced dome over the crankshaft axle, in 1958 the alloy cases were introduced.
peterg123
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Re: Swap Tim Primary for All-Alloy Cases?

Post by peterg123 »

Got it duncan, thanks indeed for your reply....... cannot the drive shaft axles be swapped on a Twin crank? Probablynot...sadly my 4 cranks were all stolen, so I have none to look at. Cheers
peterg123
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Re: Swap Tim Primary for All-Alloy Cases?

Post by peterg123 »

Will the Burman clutch plates designed for the B52 fit the AMC clutch?
Groily
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Re: Swap Tim Primary for All-Alloy Cases?

Post by Groily »

I think what Duncan says is right Peter.
The alloy chaincases were supported by a stud on a web/boss cast onto the drive side case passing through both cases just above the oil filler plug, a fixture the earlier engines don't have, so additional support for the primary cases would be needed. But it can be and has been done, with a bit of jiggery pokery.

The blanking cap on the end of the inlet camshaft tunnel needs machining down almost flush to get clearance for the inner chaincase, yes. But that's the 'easy bit' frankly with this sort of mix and match.
Don't know about the breather problem because my hybridised beast had the later flapper disc valve arrangement on the mainshaft, not the breather off the crankcase.

The Burman clutch plates won't go, no, and the mainshaft on the crank is integral on the twins so you can't change it. Chop some of it off and machines things to take the breather etc, ? maybe ?, but that's 'work' by any standards. A late crank without shock absorber, and cush drive clutch might do it with less hassle in this department, but other difficulties elsewhere perhaps. (Worth noting too that AMC clutch plates come in 2 versions - with the tangs on the outside, or the inside, of the friction and plain plates . . .)

Otherwise, mods to the outer chaincase to accommodate the shock abs would, I think, be the only option if going 'alloy'.
The pic here is of a G9 engine with shock absorber crank and dynamo alloy chaincases.

This was just one of various iterations of a cheap project bike that is nowadays back to being the Model 31 it was supposed to be all along.
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peterg123
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Re: Swap Tim Primary for All-Alloy Cases?

Post by peterg123 »

Groily thanks this has cleared up a lot of problems. Thus have ordered of EvilBay a pretty pristine set of tin cases that fell into the timing!

Pity about the Burman plates..however ifI have to fit an AMC clutch with spacer, I'll then have an engine with a crank SA and cush SA in the clutch? Will this cause any problems or do I make up a distance piece and do away with the Spring SA on the drive crank?

That bike is very smart..I love it. Esp the seat..darn the ugly-ass seat on the 51+ bikes is the worst part of it. Like what you did.
Groily
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Re: Swap Tim Primary for All-Alloy Cases?

Post by Groily »

Ha! Bit of a Farmyard Special, which is what I have always called it Peter, but it suited me like that as a 'fun' bike, and it now suits me with its original 650 engine in it with a new Club crank - and sensible footrests and controls not made of farmyard scrap!

I think people have successfully run with the shock abs AND the cush drive clutch, yes, but in my case I locked up the shock abs bit when the earlier 500 engine was in it. The 650 doesn't have the shock abs, so the question became moot in the current iteration. But I still use the chaincases - as I don't have another set in alloy.
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Re: Swap Tim Primary for All-Alloy Cases?

Post by 56G80S »

Hi Peter, not a twin but I ran a SA type G80S with an AMC gearbox and clutch. It was fine for many tens of thousands of miles.

Johnny B
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