Well guys I found the cause of the fault to night the gudgen pin has worn so badly and has flats on it. The small end bear just gave up and fell apart.
We ran a hacksaw across the pin and it is as soft as f***.
I havent sussed out how to load photos yet so lambro is doing it for me.
So all you mec crank owners can breath a sigh of relief. Lol
Serveta 200 with a snapped crank, ooops :-(
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Servetta200
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As requested:
Nothing at all to do with the crank,
True culprit is this:
Nothing at all to do with the crank,
True culprit is this:
1200 replies, and no comments/advice on why a hardened gudgeon pin would wear so much after so little mileage with devastating end results 
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carlos fandango
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Im no metal expert but, i think the gudgeon pin is case hardened. Someone much more knowledgeable than me, explained it to me once, that if its not done correctly and deep enough it can flake off. You've then got a flat spot and a piece of hardened metal flake flowing around your bearings.
When i was young my Mom said "if you haven't got anything nice to say, say nothing at all " ..................... and people wonder why I'm quiet around them !
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Grumpy225
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lambro wrote:1200 replies, and no comments/advice on why a hardened gudgeon pin would wear so much after so little mileage with devastating end results
It got hot, that's what caused the pin wear, once that happend the piston had lots extra room to move where it shouldn't, causing abnormal stresses on the crank rod.
I suspect the oiling holes in the small end were not enough to keep the bearing lubed, or at some point the motor was detonating pretty good.
I've seen similar damage on wrist and big end pins with holed pistons.
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SuspectDevice
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You say rock oil has changed from red to blue? I assume you used blue? if so its a premix oil and unless you are very very aggressive with the mixing when filling up the oil can "sink" to the bottom of the tank only partially mixed so you could well have been running with almost no lubrication 
that would have got very hot very quickly and could cause excessive component wear. Just my thoughts
that would have got very hot very quickly and could cause excessive component wear. Just my thoughts-
Adam_Winstone
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I've heard of this sort of pin wear on a Muggy some years back (prob on LCGB forum). Perhaps the plating is prone to being a little soft on these?
Up until giving Groundsman (Rockoil) a go, I'd kept well clear of Rockoil after having similar experience of Rockoil pre-mix coming out of suspension and settling to the bottom of my tank and float bowl whenever we had a cold night. Stripping the carb every time I wanted to use the bike soon went beyond being funny
. However, the Groundsman has served me well for a couple of years now so it is obviously a case of getting the right Rockoil and avoiding the wrong one.
Adam
Up until giving Groundsman (Rockoil) a go, I'd kept well clear of Rockoil after having similar experience of Rockoil pre-mix coming out of suspension and settling to the bottom of my tank and float bowl whenever we had a cold night. Stripping the carb every time I wanted to use the bike soon went beyond being funny
. However, the Groundsman has served me well for a couple of years now so it is obviously a case of getting the right Rockoil and avoiding the wrong one.Adam
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warts
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With it being soft all over, perhaps it just missed the case hardening process for some reason, and it has just always been like that. In my experience, the commonest hardening process for gudgen pins is to case harden. Hard, to limit wear, tough core to withstand the stress reversals and best of all, cheap.
If it was unhardened, it wouldn't take long to wear and start hammering the little end, at some point the lube could no longer cope, leading to catastrophic failure.
It doesn't look blue enough for the wear to be initiated by over heating. It appears from the photo to have excess heat on the little end track for sure, and the heat discolouration spreads from there. The track is well blue, but then its been hammered to buggery, the gudgen pin ends are proper colour-ish and should therefore still be hard.
I have seen lube failure at the little end a few times and there has always been far more blueing of the pin.
Must have been both noisy and vibey before failure?
If it was unhardened, it wouldn't take long to wear and start hammering the little end, at some point the lube could no longer cope, leading to catastrophic failure.
It doesn't look blue enough for the wear to be initiated by over heating. It appears from the photo to have excess heat on the little end track for sure, and the heat discolouration spreads from there. The track is well blue, but then its been hammered to buggery, the gudgen pin ends are proper colour-ish and should therefore still be hard.
I have seen lube failure at the little end a few times and there has always been far more blueing of the pin.
Must have been both noisy and vibey before failure?
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Servetta200
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Guys thanks for all the replys.
The oil issue is worrying me.
Ever since the engine was built I was using red rock oil auto lube. Never realising I should have been using the blue.
I only realised my mistake a month ago and swapped to the blue pre mix.
The trip to Woolacoombe was my first long journey using the blue.
The question is could this have been the problem to the small end wearing the gugdeon pin away, is there that much differance between the make up of the red and blue Rock oil?
Or is it like stated before I just had a pin that hadn't gone through the hardening process correctly, ( A one off and just my bad luck )
A a plus side the barrel is repairable and is being repaired as we speak, £140 including plating which I thought was very good!
The engine is stripped, cleaned and being welded this week.
Fingers crossed all goes well.
Your thoughts?
The oil issue is worrying me.
Ever since the engine was built I was using red rock oil auto lube. Never realising I should have been using the blue.
I only realised my mistake a month ago and swapped to the blue pre mix.
The trip to Woolacoombe was my first long journey using the blue.
The question is could this have been the problem to the small end wearing the gugdeon pin away, is there that much differance between the make up of the red and blue Rock oil?
Or is it like stated before I just had a pin that hadn't gone through the hardening process correctly, ( A one off and just my bad luck )
A a plus side the barrel is repairable and is being repaired as we speak, £140 including plating which I thought was very good!
The engine is stripped, cleaned and being welded this week.
Fingers crossed all goes well.
Your thoughts?
Damn i've just bought one of these cranks.strangely to replace a Mazuchelli one, that's been in the motor for about ten years,that has a ridge worn into the small end eye.I'll have to check the gudgeon pin too.Only a stage 4 MB indian 225 barrel
but it's on a GT casing which i'd rather not have to replace.
but it's on a GT casing which i'd rather not have to replace.