Keep an eye on your nuts

 Back in 1969 I had a 1964 Mini van with the BMC 850 engine and decided to give it a tune-up. I had been told by a mate that pouring Redex into the carburettor would clean out the carbon build-up in the engine – so that was what I set out to do.

I warmed up the motor first then removed the air cleaner from the top of the carb. So as not to lose the retaining nut, I screwed it back on to the stud in the carb and proceeded to pour Redex into the carb while tweaking the throttle so it wouldn’t stall.

Looking towards the rear of the van I could see a lot of black smoke from the exhaust, and the engine sounded better. I looked behind the van and the ground was covered in a black sooty deposit. Job done!

I switched off the engine and went to replace the air filter. No nut on the stud. It had unscrewed itself and fallen somewhere. I looked all round the engine bay and under the van… no sign of it. But no problem – I had another.

Next day I took the family out for a run and the van seemed to be running better until two miles from home. The engine coughed and a huge cloud of blue smoke appeared behind us. I pulled into a safe place to park and switched off – and, fearing it would burst into flames, I got the family out fast.

We caught a bus home and next day I drove the van back gently, with a trail of smoke behind me. I decided to investigate and pulled the cylinderhead off, thinking a valve had burnt out or stuck open only to find the missing nut. It wasn’t a wing nut but a square, flat one about 12mm across the flat and 4mm thick – embedded into the top of a piston. There were nut impressions all over the piston where it had hit the head before it stood on edge and punched a hole through the piston, allowing oil to