New Crankshaft

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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New Crankshaft

Postby GSAX1 » Wed Oct 10, 2012 4:37 pm

Yes, why change a design that has worked for over 50 years, based on the opinion of some guy in Holland? Crankshaft oilway blockage is not a common problem for AMC twins. Why "fix" it?

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New Crankshaft

Postby Quothcorvus » Thu Oct 11, 2012 9:23 am

Getting back on topic somewhat... are all of the cranks in this run spoken for, or are there any available if required? Thank you.
TTFN

Jon.

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New Crankshaft

Postby RogerJ » Thu Oct 11, 2012 9:57 am

Jon - you can still participate. As it stands at the moment there will be cranks for general sale to members but they will be more expensive than the price offered to those who "cough-up" now.

Contact me at secretary@jampot.com if you need further information

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Re: New Crankshaft

Postby mdt-son » Sun Nov 04, 2012 4:38 pm

Hello Markus,

MG wrote:However, if you so wish, I can ask the company that do the machining to supply your cranks with raw-machined (read unground) journals. Then you can have a go at it yourself. Machining material off the inner sides of the crank webs and subsequent grinding of all three journals should give you exactly the crank you desire. Just let me know if this is viable for you. Leaving the crank unground shouldn't be a big problem, but making one-offs during machining of the serial production run will cause tremendous additional costs I'm afraid (re-designed 3D model, CNC programming and setup costs, and we'd need at least one additional prototype with the inherent risk of rejects). So I hope you will understand that this is out of question unfotunately.


After some further discussions with Jan de Jong of ABSAF his last statement is to the effect that the G12 crankshaft center can't be made to resemble the G45 center. Exactly why I don't know. The desired center main journal would be Ø50mm x 26mm. I do not hold drawings of the G12 crankshaft. Maybe you can tell me the size of the std. center main journal?

How far are you with the batch? Are you testing the prototype cranks now?

Best regards,

Knut Sonsteby

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Re: New Crankshaft

Postby MG » Sun Nov 04, 2012 9:32 pm

Knut, the G12 centre journal is 41.07 x 22.3mm, that's why, obviously. We do have about 2mm machining allowance, but that's still far from the 50mm you'd want.
I wasn't aware that G45 cranks were that much different!

There have been some delays in the machining process of the first batch recently - mainly a lot of process optimization to minimize tool wear, ADI is a bugger to machine if the parameters aren't spot on owing to the work hardening properties of the material, and getting them right involved a lot of trial and error work together with the foundry and tool manufacturers. So we are behind schedule, but within a week or two the first batch will be done and we can start testing the cranks, and hopefully catch up with at least some of the time we've lost.
As of today, the turning and drilling operations are completed, grinding the journals to size and some millling operations are left to do.
As soon as the cranks are ready we'll post some pics!

Cheers, Markus

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Re: New Crankshaft

Postby cf160 » Wed Nov 28, 2012 9:09 pm

The picture of the rough cast new crank shows there is no center main bearing with this crank! What's with that? OR is that
massive bridge between the counterweights in the middle to be machined away? I don't understand ...
Dave(cf160)
David J.Potter

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Re: New Crankshaft

Postby RogerJ » Thu Nov 29, 2012 9:15 am

Rest assured David it will have a center main bearing!

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Re: New Crankshaft

Postby 1608 » Thu Nov 29, 2012 12:19 pm

Perhaps this might have been a good time to have done away with the centre bearing, like all other Brit twins. Especially as I've never heard a good word said in favour of it and that its probably caused more problems than it was supposed to cure, ie. vibration and breakages etc. The centre bearing is a liability with regards to oil pressure too, and there would be no need for a centre web. Annnnd ! less machining on the new crank. I think I'd best stop now as I can sense a lot of flack coming my way. Worth a discussion though, eh?

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Re: New Crankshaft

Postby petert120r » Thu Nov 29, 2012 1:20 pm

1608 wrote:Perhaps this might have been a good time to have done away with the centre bearing, like all other Brit twins. Especially as I've never heard a good word said in favour of it and that its probably caused more problems than it was supposed to cure, ie. vibration and breakages etc. The centre bearing is a liability with regards to oil pressure too, and there would be no need for a centre web. Annnnd ! less machining on the new crank. I think I'd best stop now as I can sense a lot of flack coming my way. Worth a discussion though, eh?


But the oil feed to the crank flows through the centre web to the b/end journals?

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Re: New Crankshaft

Postby 1608 » Thu Nov 29, 2012 3:05 pm

Yes, there is that of course. Suppose we're stuck with it then. What was I thinking!!

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