When in doubt change it out? yz125 rebuild time.. HELP..

Iam the proud owner of a very nice 1987 yamaha yz125.

So.. what about it.

Ever since ive owned it about 2 years now. Ive had a gut instinct that my top end is about to s*** the bed. Its weak doesnt pull to hard should be alot more grunt. I know its time but it still runs good so it leads me to think that i do not have to do it. Ive done a compression test It was negative out probably. So i got 120-135 it should be 140-175 right. I know its time id rather do it now then have the big bang in the middle of the season and be screwed right. Whos knows that piston could fatigued and ready to go. I know its been rebuilt before the bolts have all been out im thinking its had a full rebuild. Either way the top end bolts have been out theres blue rubber gasket on the reed valve but how long could this have been?

So for roughly 129.00 for gaskets and all should it. I know when it gets hot out the compression test will be lower.? so yes or no.

 

Re: When in doubt change it out? yz125 rebuild time

2 stroke race bike, from '87....................id say its been rebuilt more than once!!!

my 4 strokes with nikasil'd cylinders get rebuilt a minimum of once a year, more if we have mud races. my friends on 2 stokes usually go through 2 or 3 pistons a year.

did you do the compression test with the throttle wide open?

while you are rebuilding it, put a nice set of boyseen reeds in, and make sure the power valve is in working order.

 

Re: When in doubt change it out? yz125 rebuild time

I already scored a pair of boyesen pro series reeds off ebay. Thia is my plan ill first tear it down and check the size of the bore. Iam not going to go ordering parts before i know the bore size. But i will be buying a wiseco pro lite piston kit. And im wondering if these are any good?. Its really all i can find so im going to get it anyway a pistons a piston and ive heard you get more hours out of a wiseco then oem..its probably got a tired wiseco in it right now

 

at least with what i hear in the snowmobile world, wiseco pistons suck, but so many peolpe use em maybe its just a coincidence?

 

Well i hope they dont suck there 45 dollars cheaper then oem

 

You are going to mic the pistons and cylinders before you purchase right ?
It might already have 1st,2nd or 3rd oversized piston in it. Should the cylinder need some work, you might want to let a machine shop bore the cylinder to fit the new piston.

I let a guy here do my sons polaris, he checked it out, ordered piston/rings, bored and fitted rings for $120. Had to go 2nd over as the cylinder was too scored to just hone it.

 

Its got a 0.55mm piston in it right now which is 20 over. Its bored out to the second size. Ill have it checked out but people just want to make money. I need to find someone whos not going to screw me. The bike still runs and was just getting low on compression. The cylinder should be fine.

 

Just toss another set of 2nd oversized rings on it then!
Should work great with that new set of Boyesen Reeds.

 

tyler, mind throwing some pics up... also what happened to your 650? did you decide to jsut part it out, and there wer some people trying to get a hold of you for parts for it..

 

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650 turned out to be a money pit so i got money back by parting it out.

Iam planning on getting some ppictures soon. Another question if my bike was running and going.just getting low on compression then i shouldnt have to take to much precaution my plan was to buy new piston kit and get a light hone and be done with it.is that not good?

 

wiseco=suck, use ART

 

all this hatred towards wiseco!!! i love them! we have run wiseco, CP, JE, and athena in our machines, and honestly they are all on a pretty level playing field. wiseco has not failed us yet, or shown signs of premature wear compared to the other brands.

 

thats right.. I have heard the pro-x pistons are pretty good maybe on my next rebuild ill try em out'. But for now i just want to get it done.