YZ426F having problems

[barty5]

I thought 4 strokes were easy to rebuild

they are but some cock at a bike shop rebuilt this one and i can say cock cause the crank was set up 180deg out so who knows what else he has fucked up head is off all looks sweet valves seal nicely so they arent bent they move freely startin to think somthin more internal could be set up wrong got a few more thing to try out tommorow if time allows before cases get split as well.

[laserracer]

WOW sounds weird , you could try asking greyracer on the 426 forum on thumper, he is a master yz426 whizz ,before you split the cases ,just in case its something else ,but it sorta sounds like you have the top end covered,Hope its nothing to major
Have just had a search on thumper... it could be the counterbalancer key.... oooppps this may only be relevent to 2000 models as i think newer models had a spline

[barty5]

im hopinnot as it turned out it was the primary gear that lost a tooth not the cam so all that stuff was looked and a replaced hence the did the big end while appart. but i guess if you can get the tdc wrong anything is pos.

[cheese]

Not something stupid like the timing way out? or a sheered key for the flywheel?

[barty5]

Not something stupid like the timing way out? or a sheered key for the flywheel?

nope checked all that

[Danger]

I know you have said several times that the timing is correct but how are you checking this? By the timing marks or with a dial guage or timing light?
I just want to bring up the possibility of an aftermarket crank having been used in this bike like a Hot Rod crank or something. I know they have caused timing problems in YZ250's due to the key being slightly different to the stock crank.

[barty5]

I know you have said several times that the timing is correct but how are you checking this? By the timing marks or with a dial guage or timing light?
I just want to bring up the possibility of an aftermarket crank having been used in this bike like a Hot Rod crank or something. I know they have caused timing problems in YZ250's due to the key being slightly different to the stock crank.

poor mans dail guage and timing maeks it still has genuine crank.

[motorbyclist]

my money is now sitting on it being an electrical problem.... assuming the carbs and air filter are all good.....

[barty5]

Well its times like this you really wish you had bought that compression tester a few day earlier would appear we have a major lack of it going on which could also explain the rattle (piston slap at a guess) Knda strange as it dosent fell like it miss that much when you kick it over but it dont have any guess im more use to my 450 although not a lot a diff in motor size. Waitin on owner to find out if we go any further with it ie new piston kit.

[laserracer]

Ouch sounds all bad...$$$$$

[barty5]

Ouch sounds all bad...$$$$$

$337 retail my price $200 so as it for mate of a mate somewhere in the middle

[barty5]

Well after a lot of thinking on this job. Finally got the go ahead from the owner so pulled the piston out measured it up hmmmm ring end gap big enough for a bur to drive through dang near 1.5mm and piston clearance cant remember now but out a spec.
New piston ordered and fitted (along with another big slice in finger blood everewhere) watch sharp edges on pistons) Anyway all fitted reset timing fit tank hey starts 3rd kick motor still little noisey at top but 100 times better than before and it now starts.

JOB DONE

[krad_nz]

Wow well done mate. Enjoyed watching the diagnostic process.

[barty5]

Wow well done mate. Enjoyed watching the diagnostic process.

Fuck glad someone did i sure as hell didnt enjoy doin it. Real mind fucker you would think a b/shop would have checked the rings and shit while it was in bits given the once out it was rather easyto see it was original piston standard size, You would or at least i would at least wanted to check its tolerances. Especially when you have stripped it for a 3rd time ????????????????? Wonder why i fix my own hmmmmmmmmmmm ill ponder that NOT.

[kezzafish]

yeah well done boss. Glad it was a satisfying escapade for ya lol. The owner of the bike has gotta be pissed off with the shop but at the same time stoked you could sort it out so cheaply