Oh No!Hate it when that .... happens

[barossi73]

Gave bike a thorough clean,set about doing its 1st top end 68hrs 13 200,tank and shrouds off etc and so on.remove pv covers and gingerly disconnect p.v rod and remove actuator plate(fiddly little ...!)lift head off,looks good to me,lift barrel off,some marking but nothin you can feel where piston runs.going along nicely i get the clips and wrist pin out with minimal fuss.piston off,looks pretty good.compare with the wossner thats goin in,same profile etc(slightly different relief shape above wrist pin?).all good.clean parts.dont want to leave it open so fit new rings with a little oil.remove old needle bearing then oh no!,the supplied bearing is 3mm narrower.Hate it when that .... happens!I briefly wonder if it would matter?And what the consequences might be?Aargh!Wont be finishing this tonight...had just enough cling wrap in the drawer to wrap barrel,head and cover case!
on the plus side things look pretty healthy in there and when im at the shop getting correct part tomorrow,i can get a 2nd opinion from mechanic while givin the parts guy a windup

[Mattnzl]

Did you get the wossner from mxparts?
I never even thought to look at the top end bearing width! FWIW I've done two piston/top bearing changes with their parts and no problems (did 120 hours on the first wossner piston I put in).

[barossi73]

No,not mxparts.Have a mate in yamaha parts who sourced piston kit and bearing for a sharp price,gasket set from tracktion.thanks,good to know the wossner can take a few hrs abuse

[barossi73]

Heres a couple pics 60hr topend 13ec200,to me the jetting looks pretty good,but feel free to comment.running 95 at 40:1,measured squish at 1.5/1.6 - 1.7/1.8mm using the old orings on new wossner piston to measure.was pleasantly surprised after reports of 2mm+ being common.top of piston when at bdc was dead level with bottom of exh port so put same thickness base gasket back in(black 0.6mm?).so if jetting good,squish reasonable,only leaves oil type(belray h1r),or stealth can as spooge culprit(or both).maybe its me riding too much single track and not enough wot!
threw an iridium plug in there,good idea or no?the one in pic has 15-20hrs on it
My jetting is 40pilot,NOZH#2,175main,0-500m,15-30c summer,0-15c winter,vforce3,as2

[Neil E.]

I wonder why the difference in the piston port? Otherwise looks fine to me. Will the bore clean out OK with scotchbrite?

[barossi73]

those marks in bore are minor,nothin you can feel,and my pic shows the worst marks.was advised to not scotchbrite,just cleaned the top rim of bore above crown at tdc and threw it back together!maybe next time il give it a light workover.virtually nil sooty deposits,just a layer of wet oil over pv etc.not sure why the piston relief is shaped diff.is that even a port?hard to see how,its a dead end.update-have a grassroots mx event here tomorrow and thought id run bike in with a few restrained laps with the track build team,yeah right,within a couple minutes i was hard on it and having a blast.think its run in now!