After splitting the cases, I found the flywheel side crank seal was absolutely knackered. It had hardened and chewed itself up.
You can also see that dirt has passed through into the crankcase
That side outer crank bearing and the centre bearing have gone. A new crank I've got will be installed. This one will be repaired for 1st reserve (I've a new set of bearings).
Also found significant wear on both barrel exhaust bridges, plus the pistons are slack in the bores, so it will also get 2 x complete brand new top ends.
With the amount of miles I cover, this engine rebuild should last the bike, but its an expensive repair. Also a good lesson for everyone buying an NSR of unknown origin.....even if it looks shiny on the outside, it still needs the engine looked at internally.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30