Wanted: 84mm Stroke Crank Shaft

[dark_knight87]

Hey Guys,

Have had a bit of a disaster! - During a VMCC run at the weekend my poor '53 Golden Flash gave up the ghost!

We have stripped the engine down and it looks like the main crankshaft bearing has turned in the case taking the worm drive and oil pump, also a big end which has damaged the crank.

So, I am looking for another 84mm Stoke crank (as it will be too expensive / time consuming to repair).  If anyone has one lying in the back of the shed or the loft etc. I would be interested in purchasing it.

Thanks in advance.

Russ.

[trevinoz]

Russ, you are probably as well off repairing your crank as one from the back of the shed will most likely need grinding.
When you say the main bearing has turned in the case, has the bush only turned in the housing or the complete assembly turned? The housing shouldn't be able to turn because of it's construction but the bush can turn if it was not dowelled to the housing.
What actually happened to the oil pump and drive worm? Were they damaged by the shaft flopping about after the main was destroyed?
          Trev.

[dark_knight87]

Trev,

Thanks for the reply - unfortunatley I am a little green on classic bike mechanics so an experienced friend is doing the work (ablliy assisted by me).  I haven't seen the damage with my own eyes yet but when I'm told that the crank is scrap then that is what it is. 

Yes the bush had spun in the casing and the subsequent movement had damaged the worm drive and the teeth in the oil pump.  There has been some scratching of heads to find a reason why there is so much damage.

The other problem is the magneto is also shot - the bearings have collapsed in this also!.

Wouldn't mind but the bike was completely rebuilt in 2005, and I treat it like a baby!.

Russ.

[LJ.]

Hi Russ

Sorry to hear of your misadventures, I do have a crank of somesort I'm told its an early A10 so is not suitable for my later swingarm A10s. (unless someone can correct me on this please)

Both threaded ends are good, holes are not blocked, basically it needs a clean up. Perhaps needs a regrind what ever that is. Apart from that I have no idea of any other history, cant even remember where I got it from.

If it turns out to be of any use then make me a reasonable offer.

I'm just over at Peterborough by the way so not too far.

Cheers!

[dark_knight87]

LJ.

Thanks for finding out a crank  - I will PM you once I have got some more info from my mate.

Russ.

[A10Boy]

Sorry to hear about your troubles with your Flash.

I would agree that if your crank is grindable then it would be better to have that done as you then know what you've got. If you buy another one it might need grinding. A siezed big end can make the crank look like its scrap but I would council taking it to a crank grinding engineering company exerienced in grinding bike cranks for their opinion.

In one way, you are lucky that you didnt have a conrod emerging from the front of the crankcases - best of luck

[Brian]

Russ,

I am probably telling you what you already know but you need to have a very, very, very careful look and try to work out what caused this.

You have been riding the bike since 2005 I take it so that would indicate that lack of clearance between the crank and bush was not the problem which leaves lack of oil.

The magneto bearing failure was probably caused by the end float of the armature being too tight. The magneto has to be shimmed correctly to allow the armature to turn freely.

Good luck with the rebuild.

Brian.

[groily]

Maybe the problem started with the oil pump worm rather than ended with it? Hard to sort chickens from eggs sometimes when all is ruined . . . but long ago I had the same problem - or the same mess anyway - and I ascribed it to the pump drive. Not sure if the diagnosis was right, but it never happened again after I'd replaced all the relevant bits. However, if the bush somehow moved to cut off the oil supply . . . was it a solid bush or a steel-backed one?
A good engineering company I can recommend , not a million miles from you, is T & L Engineering, Elstow just outside Bedford. They deal with all sorts, including loads of classic engines from 2 and 4 wheels. 01234 352418. Father and Sons Talbot are true enthusiasts. Grinding, metal spraying, dynamic balancing etc etc. I speak only as a happy customer for a crank earlier this year.

[LJ.]

Russ...

Done the measuring as you asked in your IM. Picture with measurements enclosed in this message for the benefit of the members here also whom may be able to provide added advice and info.

Good luck! I hope this looks okay as I really dont know much about this sort of thing...

Let me know if you should want further photos or measurements! I'll be in all day... will send you a mobile text for you to get in touch with me.

Cheers!
LJ.

[LJ.]

Just an update!

Spent this dull Sunday afternoon in the shed cleaning up the crank. Found what might be a part number 5872 if that means anything to anyone? I also found from a friend who came round that it is a 58mm stroke But we still don't know if this is a 500cc or 650cc crank. Any one know?

[Brian]

The A10 has a 84mm stroke. Are you sure your friend measured it correctly.

You need to measure the distance between the centre of the main shafts and the centre of the crankpins and double it.

[LJ.]

Agggghhhh I just see my mistake in my last post... I put 58mm and should have put 84mm but YES Brian that is the way we measured it. Any idea what the A7 stroke is?

[Brian]

The A7 is 72.6mm. There is a earlier A7, pre 1950 that has a 82mm stroke but your not likely to find a crank for one of those.

[A10Boy]

I just want to second the views on T & L Engineering, they are a great company. i should mention that I have no connection with them.

They are the only company that the AJS and Matchless owners club trust to do their cranks, as their 650 cranks have a deep central journal which is one thou different to the outer ones and if its not ground right - Bang it goes...

[groily]

And it was an AMC crank they sorted for me A10Boy . . . you're absolutely right about that centre bearing - different size from the ends and VERY narrow, so not many people want to do them. They're pretty much the same on all the twins, except the 650s are even harder cos of the longer stroke. Plus, the radii are mega-critical  . . . lose them, and BANG indeed  (which has happened to me along with a few thousand others over the years). When I was in there, T and L had all manner of vintage car engines in; they have made special tooling for re-cutting non-detachable head 4 valve per cylinder 3 litre vintage Bentley valve seats - a loooong way up the hole, they have a dynamic crank balancer to die for, and on top of all that they are inexpensive and friendly. And they redo white metal bearings as well. They make their living on commercials etc etc, but they like bikes and have a few Santa Pod customers for whom they fettle cranks and so on. All extremely interesting stuff. They did my crank same day by prior appointment, plus sorted out some new fasteners for the rods (which are also a bit special on AMC twins) and gave me a tour of the works. By any standards they are GOOD.