Twin Crankshaft end float.

Information relating to the Matchless G12 or AJS Model 31 650cc twin
Groily
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Re: Twin Crankshaft end float.

Post by Groily »

That's very useful Peter, many thanks again. My Norton engines are well within that that, which I hope is good!
With their bushes on the timing side and roller bearings and shims on the drive, later pre-unit Beesa twins need to be a lot less (2 thou max), which I suppose has coloured my thinking over the years.
I shall pass on your thoughts very happily - also it's good to know the oversize bits will be +10 as and when. I can't remember what I measured the various thrust washers I have in my engines at now, but they are all standard I'm sure as I have never used anything other than what was there.
Cheers!
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dave16mct
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Re: Twin Crankshaft end float.

Post by dave16mct »

I was once given the part number for them, Simca/Fiat W2036S. I never found any though.
Dave.
g80csp11
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Re: Twin Crankshaft end float.

Post by g80csp11 »

Dave , absolutely correct on part number and that's what we have used as samples for manufacturing with analysis of the material
luckily i had a set as a sample
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Duncan
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Re: Twin Crankshaft end float.

Post by Duncan »

dave16mct wrote: Wed Sep 28, 2022 10:20 am I was once given the part number for them, Simca/Fiat W2036S. I never found any though.
Dave.
Just a thought would it be possible to find the end float dimensions for the car application and apply it to the bike application?
Groily
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Re: Twin Crankshaft end float.

Post by Groily »

Looking round the www there is all sorts of good reading material on setting end float on roller bearing cranks, mixed ball and roller bearings, plain ones, etc etc.
On similar plain big-end twin cylinder motorcycles of the day there are significant differences in how and / or at what stage in a build to measure things, notably due to the way oil pump worm drives pull things up tight, or drive side shock absorbers, sprockets etc. Or, there's a press-fit inner race on a ball bearing, or two even, which makes it hard. With some Triumphs, the books say from, eg, '3 to 17 thou' - but you have to measure it at the right stage. (Try measuring it with even a light press-fit inner race on a ball bearing!) Nortons at 12 thou max, etc etc.

We are fortunate, I think, with the AMC twin design not to have some of those 'side' issues (pardon the pun) cluttering things up, so I'm more than happy to adopt 'a few thou' as a sensible approach, per comment from g80csp11 Peter.
It's now in my head that 6 thou would be a nice number, but not so carved in stone that a fraction more or less would worry me. That also ties up with what I think I can remember of the last times I did my own various engines - many thousands of trouble-free miles ago. (Which I hope says something!) It's also maybe relevant that neither Neill nor any of the workshop manuals specify limits as far as I can see for these engines, whereas for many marques with just a 2 bearing crank there is a whole heap of literature.
g80csp11
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Re: Twin Crankshaft end float.

Post by g80csp11 »

in reality the end float is controlled by the thrust washers both sides of the centre web and is not adjustable . the centre web is fixed in the crankcase and the mains cant have any influence
only a worn crankshaft and or thrust washers can give excessive end float
so new crank from club machined to correct tolerance , new thrust washers will be default give correct end float
Only after considerable mileage or wear will new washers be required , and very soon we will be able to offer these for worn cranks and new cranks, one of the advantages of a three bearing crankshaft design
center web.jpg
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JEAN-NOEL
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Re: Twin Crankshaft end float.

Post by JEAN-NOEL »

Hello
Just an idea: the play between the crankshaft and the thrust washers should logically correspond to the play applied to the big ends and the main bearing. There is generally very little wear at this level, because there is not the same stress as on the big ends and the main bearing. Very excessive play is often the result of omission of the thrust washers! For there to be really significant wear, the crankshaft would have to be seriously twisted !
Kind regards.
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Re: Twin Crankshaft end float.

Post by JEAN-NOEL »

Hello
Thinking about it, I don't think you should compare the end play applicable to Nortons and Triumphs, because they don't have a centre web, and it's the bearings that regulate the en play.
In the event that the new thrust washers, standard or +10 thou are not suitable, it would I think be possible to get them re babbited. T&L Eng. have the know-how.
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