[CycleSi]

Thanks for the feedback Guys.

Firstly, we now know what happened - there is a crack in the bore of the piston that broke. That would explain why it's been overheating with no leak as such - the coolant was disappearing into the block. Also, the oil in the sump is 'mayonnaise' ish and yet the head gaskets are still fine. This reiterates it is best to avoid 400 blocks in future.

My plan to use the existing crank in a 350 block to get a 383 has gone out of the window having been reminded it won't fit due to the journals being a different size. So, assuming the crank and rods are OK l am back to lining the block, fitting new pistons and taking it from there. The good news is that there is no sign of detonation and the rest of the engine looks good.

I've had mixed reactions to using forged pistons next time as some still think KB Hypereutectic pistons are fine. What advice can you give regarding type/choice of rings and what gaps do you recommend bearing in mind it will see the occasional shot (75/100hp) of NOS?

Thanks again.....