yz 125 top end

[butters]

im picking up a 98 yz125 next monday for $300, it needs a top end. the owner said the piston is oversized and it caught the powervalve... and it needs bored or re-coated....


what would my best options be to fix it?

 

[rmc_olderthandirt]

the owner said the piston is oversized and it caught the powervalve...?

That doesn't make sense, so I am guessing you didn't hear it quite right.

What he probably said, or meant to say, is that the cylinder has already been bored out as far as it can go before you will run into the power valve. It may still be possible to bore it out but the powervalve will need to be modified to match.

The impact of this is two fold:

1) it means that the bore job will be more expensive, I would take a wild guess of an extra $50 to $100.

2) It also means that the engine has been seized and bored three or four times already, which means that you may be at the last possible bore size.

Instead of modifying the power valve I would investigate sleeving the cylinder. It costs more, but it resets you back to standard size and gives you room to bore out the next time you sieze.

You could also search the auctions and salvage yards for a used cylinder that still has some room to bore.

Rod

 

[butters]

here is a quote of what he said

" it ran when we tore it down, but the oversized piston was catching the power valve so we took it apart and never got back to it"



but i asked him what bore its on and he said 54mm..... thats stock bore, so im just guessin something freak hapend with the PV assembly

im ganna try and see if he can give me any more info on what happend....


im thinking about sending it to ERIC GORE..... to do the 144 kit. if the motor is stock bore his kit will fix the cylinder.

 

[CRASH39]

how about ordering a new cyclinder, wesco piston kit, top end crank bearing and top end gasket kit? I think that would be better. all the parts guy needs to know is the year model to order the right parts...if its new you won't have to worry about it for a while, at lest the cyclinder,it'll be a part that won't need replacement for some years...

 

[butters]

i was thinking about that also,

the cylinder is $300 new
pitson and bearings $100
gaskets $25


or

athena top end kit $500

new cylinder
new head with changeable bronze dome
new piston andbearings
gaskets
special power valve made of harder metal


i really need to figure out what i have to work with before i make a final decision.... is there a chance the powervalve assembly got effed up and needs replace? something causing it to petrude into the cylinder?

 

[butters]

ok, i just got back to me and said its on its 2nd bore....

 

[butters]

im prolly going to get the athena factory kit.... mainly because it includes everything in the top end....

does anyone have any experiance with these kits? is there any gain in power? i know they are stock bore, but maybe they have some aggresive portwork.....