Hi. can't be old age, i can remember--well remember what i [still] do here in nz which is use a 2x5 piston kit [yamaha yz400 1979 only 82mm], did years ago use [i think] a ts400 or tm with brass bushes to step down the gudgeon eye of piston to the Yam pin size, must have drilled holes in skirt or cut it away [can't remember now] but two of them broke up after a while. Then got onto the 2x5 kits which are genuine Yam, strong with the big cut away on the inlet side not just a couple of piddly little windows. I trimmed a bit off the bottom of the first one as gets close to the crank wheels a bdc but forgot the second one & is running ok [got me worried now]. Just got a 'hybrid' 360 going having downsized with a 250 crank [just because--old n stupid] but will probably do the 82mm piston to that as only had an RT1 non reed piston to use for testing [with hole cut in skirt], now i've proved it works i'll use the good piston kit so i can give it a [damn good thrashing!!] without worrying about piston destroying itself. Anyway--where was i--take me pills & sleep. Oh yeah, might have to take the edge of the head squish area out a mm or two as we're talking 82mm std as opposed to 80mm on all the 360's [81mm max yam 4th over rebore]. Sorry, i've been doing this on an RT2/3 but should work the same on RT2mx & MX360, not sure with YZ360A/B as think Yam only allow .25 rebore as have a thin liner [have yz360b cylinder here & looks original liner & parts show only 80.25 on the 360. Might get to 80.50 ok but not 82mm i'd think. Confusing myself so there endeth the lesson. Cheers O.T.H.
