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[JTL]

First picture shows exhaust side to the left. Second picture shows the left of the intale side. Third picture shows ... well, the sparkplug. Fourth picture shows the damage to the conrod. Hope this helps answer some of the questions and maybe rise more questions.

[Alan R]

What sort of end-float have you got on the crankshaft ??

[Tim NZ]

No evidence of detonation on the crown or the s.plug so my money is on it simply being a faulty piston.

[papasmurf]

It looks to me as if there is porosity in the piston in the un-machined part of the piston. (2nd picture posted.)

That is always a bad sign. If I saw that in a machine shop I would not have machined it.

[Gwilly]

Is it possible that the pin has become seized on one side of the piston (lack of lube) seems to be scored/blued before busting the cast.

Piston crown and skirt look in good nick for 19000 kms as do the ring lands..

You haven't been over reving after a gold star have you???

[JTL]

Allan R... if you by end float mean sidewards movement at the crank shaft, there is none. Tim... I tend to believe the same, but the again a specific type of stress to the metal coursed it to break at that exact moment. Papa... I believe it's a sand cast which leaves this kind of surface to the metal; I don't think the look has somethng to do with porosity. The rest of the machined piston looks super smooth. Maybe it's just made out of used Cola cans? Gwilly... yes, the overall apperance of the piston is good. The pin has a nice, free feel in the small end. It doesn't have any discolouration beyound wear and hot oil. I'll try to make some pictures of the pin for upload. And, yes, it happened during acceleration (45 kmh to 50 kmh), but no Gold Star pursue this time... Maybe all of this has something to do with my riding style. I like to ride the bike hard, but in general I don't ride it fast. I have the occational 110 kmh for very short distances. Otherwise it's city traffic and small country roads... regards Jacob

[papasmurf]

Take a close look it is porosity.

[JTL]

Papa... regarding porosity, please direct me to what I should be looking for and where to look for it. Can you make an arrow in the picture as Gwilly did, and also explain to me what details to focus on? Right now I'm not quite certain about what to look for... regards Jacob

[Alan R]

Hi JTL------- porosity is basically lots of small emty pockets where gas bubbles formed when the Aluminium was being cast..................Have a look at this}---------https://en.wikipedia.org/wiki/Hydrogen_gas_porosity

[Tim NZ]

Porosity:


I sent a piston back to the factory that had so much porosity, petrol was able to pass through the crown!


Does not say too much for the ISO 9001 QA.