Author Topic: opps!!  (Read 3725 times)

Offline Rich

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opps!!
« on: 19.05. 2013 18:38 »
Will araldite fix this?
Large journal crank required




Online chaterlea25

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Re: opps!!
« Reply #1 on: 19.05. 2013 18:58 »
HI Rich,
The cause of the disaster is almost certainly down to incorrect grind radius when the crank was ground previously
 *sad2* *sad2* *sad2*
Sorry cant help with a crank, they come up on fleabay fairly regularly but are getting very expensive  *ex* *ex*

HTH
John
1961 Super Rocket
1963 RGS (ongoing)

Online bsa-bill

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Re: opps!!
« Reply #2 on: 19.05. 2013 19:27 »
Not the recommended way to remove the sludge trap ;)
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

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Re: opps!!
« Reply #3 on: 19.05. 2013 20:02 »
 Bugga, but the cam still looks OK, how about the cases?
I agree with John, bad radius. They should be 80-90 thou and almost a mirror finish.
Cheers.
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline Rich

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Re: opps!!
« Reply #4 on: 19.05. 2013 20:46 »
Cases, conrods all ok.
just over a year ago, at Shepton Mallet I sold a large journal crank on -30thou thinking I would no longer need them, but kept my thick flange barrels in case I ever did, wrong decision.

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Re: opps!!
« Reply #5 on: 19.05. 2013 22:39 »
 I'd get the rods checked for alignment.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online Greybeard

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Re: opps!!
« Reply #6 on: 19.05. 2013 23:31 »
OMG!
That is awful. I hope you are able to source a crank quickly. What speed were you doing when it failed?

Offline bikerboy

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Re: opps!!
« Reply #7 on: 20.05. 2013 00:02 »
I have a crank I picked up as a spare from ebay but I have not measured it so it probably needs a grind, I could measure it if you have not sourced one yet. I think I paid £100 odd quid for it a couple of months ago

Online KiwiGF

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Re: oops!! (crankshaft broken)
« Reply #8 on: 20.05. 2013 00:42 »
Even tho the exact thing happened to me on an LJ crank (59 Super Rocket) over 35 years ago so this looks horribly familiar.....I concluded it was the incorrect radius at the edge of the journal.....the machine shop I used to regrind the ends on that crank did not seem to be aware how important that was, although to be fair, I did not either, so did not give the shop the instructions on radius required, or check the crank after the grind.

One thing to remember when buying a crank, it's generally not possible to correct an incorrect radius, once the metal is gone, you can't put it back!

On my SJ crank the machinest just did the best he could given on the prior grinds the radius had been made a bit small, and I only wanted a grind down to the next undersize.

Out of interest, does anyone know if this same mode of failure occurs on SJ cranks? Or is it just a problem with LJ?

From what I've heard, contrary to popular opinion, the SJ crank is not THAT much more prone to failure than the LJ, even under race conditions.

The SJ has wider journals than the LJ, so big end bearing area is not that much different to the LJ, and the SJ has a smaller sludge/oil supply drilling through the journal (not that that part of the journal adds much strength anyway).
New Zealand

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Offline Briz

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Re: opps!!
« Reply #9 on: 20.05. 2013 01:23 »
Thats a bad bit of luck there. Hope it didn't take too much out with it.

Regarding small-journal cranks.....yes, they do fail in the same way! I had one go in a similar manner on my first A10 many years ago. Funny enough, nothing came apart, just locked up. Wasn't until it came to splitting the cases that the breakage became apparent.

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Re: opps!!
« Reply #10 on: 20.05. 2013 03:53 »
Yep, had two A7 SJ's go. One on the right and one on the left. But wasn't doing your average road speeds  *eek*.
Cheers.
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline Rich

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Re: opps!!
« Reply #11 on: 20.05. 2013 08:39 »
I have only just aquired this bike, previous owner now passed away, however apparently he had a problem whilst riding in France but managed to get back to blighty, and the engine was turning over ok, but a low down small clunk could be heard, if you look at how it has broken, when it was all together it was sort of keyed and turned ok.
Biker boy where are you situated, as I may need the crank, I am just waiting for another person to look in his workshop and should know later today. I expected to have to have a regrind on all journals on any replacement as would not be able to afford one that was completley done, that way a bit out of the pocket bit by bit.
I will be checking the rods for alignment today, but initially they look ok, as previously stated the enginge was turning over ok but had this slight clunk, so in one way it was lucky as I think the crank just cracked in stages, looking at the stress marks on the break and stayed together.

Offline Briz

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Re: opps!!
« Reply #12 on: 20.05. 2013 10:38 »
Looking at that pic again, dont you just love the way the sludge-trap-plug threads end exactly under the fillet radius? *eek*

Offline Rich

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Re: opps!!
« Reply #13 on: 20.05. 2013 20:50 »
Biker boy I have sent a PM to you
Regards Richard

Offline bikerboy

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Re: opps!!
« Reply #14 on: 20.05. 2013 23:38 »
Got it and replied :)