Bought and installed Athena works kit, supposedly based on the european yamaha works configuration. '02 YZ125 had little bottom to start with (bolstered somewhat by procircuit and vforce) now has lost some low-end, but gained a ton of overrev and pulls hard forever. Kit includes cylinder, insert head, exhaust valves, flat-top piston, ring & pin and a very complete Athena top-end gasket kit, for about $600. You have to pull the power-valve assembly apart and reassemble it in the new cylinder with the new valves, modify the holes on the headstay brackets and toss the head-alignment dowel pins (they didn't align). Those last two weren't listed in the instructions and were a little scary, but once the thing went together we drained the tank, filled it with fresh 110 and premix, broke it in, then took it to the races where FastPuppy took 2nd in the 125 open! Liking it so far!
