Dynamo strap retaining stud, twin, broken

Information relating to the Matchless G12 or AJS Model 31 650cc twin
Groily
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Dynamo strap retaining stud, twin, broken

Post by Groily »

Sometimes the good Lord hides his face behind a cloud and smirks as things go pear-shaped . . .

Yesterday, took the Mod 31 for a typically good thrash, and upon my return spotted the dynamo strap was adrift at the 'top' fastening, where the stud in front of the barrels had snapped clean off - part-way down the 'ole (of course).

Despite my being able to cut a reasonable notch across the remnants using a v sharp chisel, even with an impact driver & local heat, no joy. Well stuck . . .
'Tis a pain, and not the first time this particular part has caused grief on a twin round here.

The degree of grief is disproportionate sadly, as it'll have to be engine out, and possibly even a full strip down, given that the threaded hole passes clean through the cases (or does on the other crankcases round here). So drilling out, retapping or helicoiling if necessary, even maybe a bit of alloy weld to buttress the slightly damaged boss where the stud obviously fretted before self-destructing, could be just too risky with the engine in one lump. Ouch.

Oh well, something to do on damp winter days - but for 'work required to remedy pettifogging fault' I can't think of anything more annoying! And out with something else for my normal Saturday morning 100 mile there-and-back jaunt to meet the like-minded.
g80csp11
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Re: Dynamo strap retaining stud, twin, broken

Post by g80csp11 »

If there is still some thread left , get a stud and drill down center on the lathe to guide a pilot drill into the broken stud . then try a easyout and if that fails drill and retap hole. you are right indoor job in the garage over the winter
Mick D
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Re: Dynamo strap retaining stud, twin, broken

Post by Mick D »

Hi Bill

Try getting a set screw of the correct thread and cut it so as the head is just proud of the engine case when screwed into the hole occupied by the broken stud. Drill down the set screw to form a tube with suitable wall thickness. Now MIG or TIG the set screw onto the stud by welding inside the hole - cross fingers and spanner the broken stud out ;)

Regards Mick
Groily
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Re: Dynamo strap retaining stud, twin, broken

Post by Groily »

Thanks Gents!

I think I'll be able to get the remnants out OK and sort the hole out. It's busted off about 1.5 turn's worth down the hole. I'm not too bothered about that side of it just yet - unless the little raised boss on the case turns to powder and leaves me with inadequate thread depth for a new stud. Creating the need for a splodge of weld. In that case I'd be calling a friend as I can't weld ali myself.
No, the PITA is having to take the engine out for a first proper effort, and then if that's no good, maybe having to strip it to get that c/case half on the bench.
I don't at all mind taking things apart when there is something seriously amiss, but for one broken stud on an otherwise tip-top motor, it is a bit depressing! And it was a new stud when I put the thing together about 15K miles ago.

On the upside though, gave me a chance to wind the P11 up a bit on dry-ish B roads this morning - always a pleasure. (Until tomorrow morning, when neck, back, wrists and a few other bits will complain they've been subjected to unnatural stresses!)

Will let you know how I get on in due course (or should it be due 'curse'?).
ajsph
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Re: Dynamo strap retaining stud, twin, broken

Post by ajsph »

place a nut over the broken stud, give it a blob of weld, and you can turn the stud out without damage to the crankcase
Poul
Groily
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Re: Dynamo strap retaining stud, twin, broken

Post by Groily »

Thanks Poul - but it's broken 'down the hole' - ie below the level of the crankcase.

The only thing I've been able to get on it with the engine still in place, is a long small chisel to create a slot of sorts. But that hasn't done it, even with heat and an impact driver. Didn't think it would really.
It's a rotten angle to play at, frame downtubes get in the way, and I don't want to apply too much whacking anyway . . .

Very hard to get a drill on the thing, although I do have a small right angle attachment that can be got into position, if not held too well, and also flexible dremel-type drives (same issue though). I'm not a fan of eezi-outs on small diameter fasteners (this is quarter inch) owing to their tendency to splay out the hole you've just made and make life worse. Mick's thought would work if the thing were broken further in, maybe.

Long and short of it after another hour staring at the darn thing just now is that I don't think there are any safe short cuts - I'd say '50/50' for a fix with engine on bench, but if that's no good, will have to take it apart I fear.
The hole isn't blind (I don't think, other cases I have here aren't anyway), and it's not that deep either, so any 'drill-through' methods of extraction (and thread repair if needed) risk putting swarf straight into the exhaust camshaft area and beyond. Been here once before 40+ years ago with my Mod 20, and I remember the pain of having to strip the engine after failing to contrive a suitable belt and braces arrangement round the cylinders to hold the dynamo strap firmly in place.

The difference this time round is that the Mod 31 isn't my sole daily transport - the Mod 20 was back then, so it was a long old weekend sorting it out without a proper shed.

Looking on the positive side, at least it's winter, and it will be instructive to see how well my Club crank and Thunder rods look after a few miles if I do have to go there.
G15 Roy
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Re: Dynamo strap retaining stud, twin, broken

Post by G15 Roy »

May be some of you attempts could be recorded for the jampot magazine
Roy
Groily
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Re: Dynamo strap retaining stud, twin, broken

Post by Groily »

'tis a thought Roy.

I'll take some pix along the way and see what Les thinks. (Well, as long as I don't embarrass myself by making a pig's ear of the job, in which case the less said the better!)

Cheers!
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les ward
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Re: Dynamo strap retaining stud, twin, broken

Post by les ward »

I'd be more than happy to print your exploits. It won't be the last time this happens to someone, Les
MalcW
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Re: Dynamo strap retaining stud, twin, broken

Post by MalcW »

Just glue the dynamo in place. It'll be fine...

Malc
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