Splitting crankcases

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Gstovold
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Splitting crankcases

Post by Gstovold »

Hi,

I am trying to split the crankcases on my Model 20. The drive side one has a crack that I want to repair. I am hoping to do this with the minimum of strip down.

The engine is out of the frame. All bolts securing the cases removed. Both cylinder heads removed. Drive side barrel removed. A partial separation of a couple of millimetres has been achieved. I have not removed the drive side piston but can see that I will probably need to.

I am now nervous about trying to proceed further because I do not know whether it is actually possible to just pull off the drive side crankcase without any stripdown or removal of parts from the timing side. The book does not help much because it naturally assumes you want to do a full stripdown.

Any advice from those better acquainted with these engines much appreciated.

Geoff
Geoff Stovold

AJS Model 20
Norton International
Velocette LE
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Royal Enfield Himalayan
SPRIDDLER
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Re: Splitting crankcases

Post by SPRIDDLER »

Geoff.
Sussex section have a Zoom meeting tomorrow night and what a couple of the lads don't know about twins isn't worth knowing.
If you're not on our section group email list you won't have received the Zoom details so let me know and I'll have you added so that you can join in.
'There is a tide in the affairs of men
Which taken at the flood............'
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Gstovold
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Re: Splitting crankcases

Post by Gstovold »

Thanks Spriddler that sounds great. Please invite me. My email is geoffstovold@gmail.com
Geoff Stovold

AJS Model 20
Norton International
Velocette LE
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Groily
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Re: Splitting crankcases

Post by Groily »

Tried to post a pic of a drive side case with centre bearing web in place, to help show what's what. But even with recent site enhancements, a tad too big to load.

However . . . The crank comes out (and goes together) fitted in the centre web and drive side half, but the timing side barrel also has to be off, and the piston. The t/side connecting rod will then pass through the cases towards the drive side, at bottom dead centre.
Camshafts can be left attached to the timing side and the timing pinion on the crank end should pass through no problem.
Little bits and bobs like the oil filter and the oil distributor bush driven by the ex camshaft etc would be best removed from the drive side too.

You can't get just the drive side off and leave the crank in place -it doesn't work that way sadly and it makes for a bit of work. (It's almost as bad as playing with our LE Velos!)

The Sussex guys will be able to explain all, with arms waving and other visual aids! Best of luck!
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Gstovold
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Re: Splitting crankcases

Post by Gstovold »

Thanks Groily. If I interpret what you are saying correctly it is this: I need to remove timing side barrel and piston and presumably drive side piston. Then if I pull off drive side crankcase it will come away with the crank attached (conrods at BDC). Then presumably I can remove the crank leaving just the crankcase that I can then take off to a specialist for repair.

Don't mention LE Velos! Got one of them. Just sorting stuck clutch was near mission impossible!
Geoff Stovold

AJS Model 20
Norton International
Velocette LE
Sunbeam S8
Royal Enfield Himalayan
Groily
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Re: Splitting crankcases

Post by Groily »

Yes to all of that, subject to any better wheezes and counsel from the Sussex people.
And LEs, oh yes. Got too many of the t-shirts awarded as hard-won battle honours in that department. But have to admit I do like mine. If they weren't so delightfully quirky there'd be no point in having them I suppose!
But then I like far too many things (my wife says).
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Re: Splitting crankcases

Post by SPRIDDLER »

Gstovold wrote: Tue May 04, 2021 11:49 am Don't mention LE Velos! Got one of them. Just sorting stuck clutch was near mission impossible!
I bought a 'complete' LE unseen from an ad in Old Bike Mart. Both cyl heads were cracked due to the coolant water freezing and the gearbox lacked any internals. I immediately advertised it honestly on eBay and it sold for 200 quid more than I'd paid. The buyer admitted when collecting it that he just wanted the reg'n number. I suspect he must have fiddled that as it would never have got the necessary (at that time) MOT without considerable expense.
Groily wrote: Tue May 04, 2021 2:09 pm Yes to all of that, subject to any better wheezes and counsel from the Sussex people.
With the average age of the section being around 70 there's plenty of wheezing. We discourage beer drinking during Zoom meetings otherwise the old boys tend to disappear off the screen on a 'need to go' basis.
'There is a tide in the affairs of men
Which taken at the flood............'
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Re: Splitting crankcases

Post by Groily »

SPRIDDLER wrote: Tue May 04, 2021 4:09 pm We discourage beer drinking during Zoom meetings otherwise the old boys tend to disappear off the screen on a 'need to go' basis.
Having just got in this very eve from one of those invasive sessions where both parties pretend to focus on anything other than the job in hand . . . I think beer-avoidance is a good strategy Neville. I shall take medicinal wine, of course, to help with the recovery. I know you'll understand . . .
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Re: Splitting crankcases

Post by ajscomboman »

What you're trying to do is not possible, I'm sorry but it's a full strip to swap out the drive side. The centre web is bolted to it and the cam follower spindles are a tight fit in the case as well. Whilst it will come apart I can't see how you'll get all the followers and spacer plus cam tunnels to line up. The engine is designed to be built from the drive side laid flat and then the timing side slipped on with the cams in.
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Gstovold
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Re: Splitting crankcases

Post by Gstovold »

Thanks for your input. You seem to be saying I may well get it apart but putting it back together again the same way will be virtually impossible. I am joining a zoom meeting tomorrow with some guys that know a lot about these engines. I shall make sure I put this point across.

Thanks Geoff
Geoff Stovold

AJS Model 20
Norton International
Velocette LE
Sunbeam S8
Royal Enfield Himalayan
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