Strange, this is not common for the 91 FX as it is ringed and has a steel liner, so this is not the usual peeling syndrome that is haunting OS. I have a 91FX myself and I am very happy about it. Anyway high rpm alone can not have caused this, I have ran mine at almost 13000 rpm on 13-6 props and it has no problems in doing this.

I have no idea what happened here, pictures would be great.

I am alittle puzzled by your mates telling you that the making of "friction noise" is normal for this engine. There was no such thing with mine, not during run-in or later. My guess is that there was something wrong with your engine from the very first start.

It is never cost effective to repair an OS, maybe a ring or the bearings, but otherwise just get a new engine.