It's not Ford related but I could really use your help

A few weeks ago my brother was riding his 2001 carb'd R6 home from work when all of a sudden it started bellowing smoke (don't know colour) out of the exhaust. I'm told it also started making some "strange" noises. He managed to ride it home but it wasn't running properly and sounded like it was running on 3 cylinders.

I've just been round with my dad to have a look and it no longer smokes, doesn't make any "strange" noises but it's still only firing on 3 cylinders. It does now pop and bang out of the exhaust which I assume is unburnt fuel from the non-firing cylinder.

We've changed the plugs all of which were a bit on the black sooty side (not oily) and also swapped the coils round (coil on plug). All plugs spark fine and it's getting fuel but cylinder 1 (left hand side if you're sitting on the bike) still doesn't fire.

We didn't have access to a compression tester but if we covered the spark plug holes we could feel some compression which felt the same accross all 4 cylinders. Not very scientific I know but it's all we could do.

The only other thing of note was there seemed to be a fair amount of bluey coloured (oily?) smoke coming from a crank case breaker. It wasn't excessive but it was visible.

It sounds like he may have holed a piston but I would have expected to see oily smoke from the exhaust but there's none

Any ideas?

James