As title says whata the difference between standard 3mb/3bn top end an 4fu nikosill is there much difference in performance? Got chance of a cheap 4fu top end in decent condition but as far as i believe nikkosill barrells cant be rebored have to be resleaved which is expensive compared to £30 for a rebore piston an rings so just wondered what the performance increase is linely to be???
Put it this way. My barrel is on its original sleeve (3mb barrel). When I rebuild the engine I'll be resleeving it. For peace of mind I want to run original bore size since the chance of hitting the YPVS is increased when the barrel is bored out.
Nikisil playing adds an extra 2-3bhp due to the smaller clearances. You'll find all the motocross bikes run them.
But yeah, you pay the price if you score a barrel. If you use quality piston kits and good oil you should be ok though. They can be re honed I believe.
