As mentioned elsewhere, I've taken on another 851 project. The last one is complete, and should be going off to a new home soon.

Mick Dixon posted on these forums last weekend about his 1991 851 that had a bit of an engine failure. We spoke that evening and a deal was agreed.

It'll probably be a few weeks before I really get started with this project properly (I've got my 916 Strada on the operating table at the moment, getting her recommissioned after a few years of being tucked at the back of the garage).

However - Mick has done an amazing job of packaging everything up (thanks Mick!) and I'm starting to organise the garage and have a look at the bits and pieces. Here's what Mick said:

Unfortunately last July my beloved 851 suffered an engine failure. The engine has been stripped by V Due Motor Cycles of Lincoln where it was found that front cylinder piston had failed….. The piston skirt had broken away resulting in a damaged barrel as well as piston.

Of course, curiosity got the better of me:

True enough the piston skirt is broken, and the oil control ring is missing:

Mick tells me that they didn't find the missing piece, nor fragments of the ring - I presume that it was quickly ground and I'll find it when I cut open the oil filter in due course.

There is some scratching on the interior faces of the piston, and a curious score around the circumference of the gudgeon pin hole - I can't immediately see any obvious damage to the gudgeon pin itself, and the face of the piston is just fine.

It's clear that the barrel is obviously now also very, very second hand...

Mick tells me that the crank was checked to be just fine - and that certainly looks to be the case:

I'd be interested in any opinions or insight as to what actually caused the piston failure. The break line on the piston looks like it shattered, though some of it has been worn to a slightly smooth feel (presumably from the ride home that Mick had with lots of debris in the engine). If it is a shatter break, then I'd have expected that to be caused from impact - but with what? - could it have been the oil control ring that shattered, and the fragments of that caused the skirt to break maybe?

I'll try giving the fella that tore down the engine a call next week to hear what his observations were when he opened it up.

Mike