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The symptoms of a 3 bearing crank failure?

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The symptoms of a 3 bearing crank failure?
Ruairidh Dunford Offline
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#21
09-11-2018, 08:06 PM
That’s a belter Chris.

I must post up a photo of the rod that failed in our Twelve - the engine still ran. Will come back...
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Terrytuned Offline
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#22
09-11-2018, 08:25 PM
Here are a couple of 2 bearing Phoenix 1 5/16" cranks that came out of race engines I would only advise an 1 1/2" crank for racing.

Terry.


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.jpg   20130923_181703.jpg (Size: 63.53 KB / Downloads: 428)
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Bob Culver Offline
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#23
09-11-2018, 08:40 PM
Hi KC
Your post appeared while I was still pondering.
It is not as classic as most. I am not sure where final fracture is. Usually crack starts at inside and works outward, but seems to have formed at outer diameter. Is it from an engine in normal use or high rpm?
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Ruairidh Dunford Offline
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#24
09-11-2018, 09:10 PM (This post was last modified: 09-11-2018, 09:45 PM by Ruairidh Dunford.)
Those are spectacular failures Terry!

This rod was in the ‘26 Heavy 12/4 - we were returning to Bristol after a long weekend in Lake District.  As we passed Gloucester on the M5, doing about 45/50mph, there was an almighty bang and tremendous vibration.  My father pulled over and eventually we were relayed the last 25 miles home.

On stripping there was no sign of the piston - just thousands of tiny aluminium pieces.

The rod was in the sump and the engine still ran.  This rod is about twice the size of an A7 one.

   

   

   

I always thought it would make a good novelty toolbox handle...
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Reckless Rat Offline
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#25
09-11-2018, 09:40 PM
Just curious, why is the 1 1/2" crank more favoured for racing than the 1 5/16ths? Is is something to due to harmonic resonance or just less overall mass?
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Chris KC Offline
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#26
09-11-2018, 10:56 PM (This post was last modified: 09-11-2018, 11:10 PM by Chris KC.)
(09-11-2018, 08:25 PM)Terrytuned Wrote: Here are a couple of 2 bearing Phoenix 1 5/16" cranks that came out of race engines I would only advise an 1 1/2" crank for racing.

Terry.

Crikey
(09-11-2018, 08:40 PM)Bob Culver Wrote: Hi KC
Your post appeared while I was still pondering.
It is not as classic as most. I am not sure where final fracture is. Usually crack starts at inside and works outward, but seems to have formed at outer diameter. Is it from an engine in normal use or high rpm?

Must admit I've been re-examining it myself and wondering the same Bob. I'm no expert but I reckon it's 2 cracks which have met up in the middle. Evidence slightly obscured by the subsequent mashing together. It was an engine in normal use by a 20 year-old student <ahem>
(09-11-2018, 09:10 PM)Ruairidh Dunford Wrote: Those are spectacular failures Terry!

This rod was in the ‘26 Heavy 12/4 - we were returning to Bristol after a long weekend in Lake District.  As we passed Gloucester on the M5, doing about 45/50mph, there was an almighty bang and tremendous vibration.  My father pulled over and eventually we were relayed the last 25 miles home.

On stripping there was no sign of the piston - just thousands of tiny aluminium pieces.

The rod was in the sump and the engine still ran.  This rod is about twice the size of an A7 one.

I always thought it would make a good novelty toolbox handle...

'the engine still ran...'   Impressive!

It's the M5 triangle Ruairidh... mine went within pushing distance (you could get away with it in those days) of Taunton Deane services, luckily not so far that Dad couldn't come up and trailer me home. Apart from one occasion when I was still running but decided not to chance it, the only time she's not come home under her own steam (looking for wood to touch...)
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Zetomagneto Offline
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#27
09-11-2018, 11:20 PM
(09-11-2018, 09:10 PM)Ruairidh Dunford Wrote: Those are spectacular failures Terry!

This rod was in the ‘26 Heavy 12/4 - we were returning to Bristol after a long weekend in Lake District.  As we passed Gloucester on the M5, doing about 45/50mph, there was an almighty bang and tremendous vibration.  My father pulled over and eventually we were relayed the last 25 miles home.

On stripping there was no sign of the piston - just thousands of tiny aluminium pieces.

The rod was in the sump and the engine still ran.  This rod is about twice the size of an A7 one.







I always thought it would make a good novelty toolbox handle...
Interesting, obviously the piston failed, usually it is the rods that fail in the 12/4 and result destruction is comprehensive
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Ruairidh Dunford Offline
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#28
10-11-2018, 12:28 AM
The overwhelming opinion at the time was that the big end bolt had let go first.
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fatcatvera Offline
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#29
10-11-2018, 12:33 AM
I’ve managed to get the engine out of the car and mostly apart this evening. The crank has failed across the web to the rear of the centre main bearing. Very similar to the image that Rauiridh has shared. It hasn’t quite cracked the whole way across the web yet - there’s still about 10mm of joined metal. I can imagine the mess it would have made of the crankcase if it had failed completely.

I’ll upload some images when I’m at a computer (I’m writing this from my phone).

Chris KC - it is indeed a small world! My brother told me he’s had a chat with you - have a you got a spare 3 bearing crank?!

Ray
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Tony Press Offline
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#30
10-11-2018, 12:44 AM (This post was last modified: 10-11-2018, 12:59 AM by Tony Press.)
Our Club Secretary had a comprehensive engine failure with a Club three bearing crank when returning from a Club run earlier this year. The faiilure is through the rear web.

He has now has a new engine with a two bearing crank.


.jpg   John McMillans Crankshaft failure 1.jpg (Size: 52.07 KB / Downloads: 325)


.jpg   John McMillans Crankshaft failure 4.jpg (Size: 72.1 KB / Downloads: 323)


.jpg   John McMillans Crankshaft failure 3.jpg (Size: 67.25 KB / Downloads: 322)


.jpg   John McMillans Crankshaft failure 2.jpg (Size: 70.19 KB / Downloads: 321)
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