As a general rule, lack of bore lubrication is likely to cause a piston skirt seizure rather than a melted piston. Need more information to be sure. A picture(s) would help. However, a melted piston is usually characterised by a nice little hole in the piston crown and/or material lost from the piston at the lands of the piston ring grooves or the top edge of the piston diameter. The rings themselves are often stuck firmly in the distorted ring groove. A melted piston crown, in my experience is almost always due to an ignition timing and/or fuel lean condition. It can also be exacerbated by the wrong (too hot) spark plug grade. Under unfavourable conditions, that itself can damage a piston. Buell changed the plug grade (6R12 to 10R12 from memory) years ago partly because of some instances of piston issues, usually rear cylinder if I recall correctly. HTH.

How did you melt them? Have you been playing with maps?

That’s the sting in the tail from free maps with no pedigree... Pistons don’t melt on standard maps on a well maintained bike...

Thanks 03.

I've melted a few 2 strokes in my time and agree with your comments.

Pretty solid engine guy called it fuel washing straight away so I will go with his assessment. (He does rebores, head skims etc)

I would be grateful to hear from anyone who has cast pistons in their xb and any other views on that issue.

Obviously forged are better. But five times better?

I think you're kind of missing the point here. It matters not in the slightest how your pistons were made. If your fueling and/or ignition are compromised, then even if you make them from solid unobtainium, you will damage them. If you truly have cylinder bore washing then you are over fueled by some margin and what Dr Pashley says is likely near the truth. How the pistons were made is irrelevant in that case.

and Its’ a wonder that with that amount of bore wash ,the over fuelling hasn’t diluted the oil and compromised it lubrication properties and done damage somewhere else

I think you're kind of missing the point here. It matters not in the slightest how your pistons were made. If your fueling and/or ignition are compromised, then even if you make them from solid unobtainium, you will damage them. If you truly have cylinder bore washing then you are over fueled by some margin and what Dr Pashley says is likely near the truth. How the pistons were made is irrelevant in that case.

Fortunately, it's a rolling element bearing engine so more tolerant than a plain bearing motor. Long term, no doubt the cam shaft bearing bushes would be worn (and the lifters and rocker arms) but I get the impression this motor didn't travel too far after the ECU had been monkeyed with?

Seems to me a that rebore and new pistons (no need to worry about how they're made) will be required along with an ECU re-flash back to stock as a minimum. Plus a couple of engine oil flushes once it's running again.

PS - I presume you've checked to see if the engine oil stinks very strongly of petrol?

I'm just trying to fix my bike and feed my children at the same time. I need an informed opinion on cast Vs forged pistons.
The overfilling (or whatever it was) will be dealt with once it is all back together.