Bore Kit for 00 YZ 25

Joined
Jul 6, 2001
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#1
hey i was just wondering what does everyone think about a bore kit for a 125 like the one i have. What do u think i should get i hear there is a 139 that is good and fast but then i hear a 144 or 150 kit just tell me what u think cause im not sure on what to do just wondering cause i have an extra cylender for my bike and just curiouse on what i can do? thanx alot and help me out on where i should send it too get the bore job and ****? thanx alot peace out ya all and keep rippin it up out their.
 
Joined
Jan 5, 2001
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#2
Id say go with wattever Eric Gorr does, if he does 144 its probobly the biggest reliable bore you can go with, 150 might be too big and eventually end up puncturing the cylinder into the water jackets. Plus the company that makes the pistons for there 150 could go out of business. Theres probobly a reliable piston source for the 144. The other problemo is that when you go to sell it people wont like it because they wont know if its
1.legal for racing
2.if they can get pistons for that bore
If you have some money to burn, and the rest of your bike is in good condition, then it sounds like a good idea, ask if porting comes with the boring.
 

EricGorr

Super Power AssClown
Joined
Aug 24, 2000
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#3
The actual sizes available are 133cc 56mm (Wiseco 726MO5600) 139cc 57mm (Wiseco 631MO5700) 144cc 58mm (Wiseco custom EGORR) and 155cc 60mm (Wiseco custom RPM).
The 133 & 139 don't require crankcase mods for piston clearance but the bigger sizes do. The 133 is a good choice and the pistons are never likely to go out of stock for more than a period of 2 weeks. The 139cc piston is a Wiseco oversize for a 1993 YZ125 and those could be out of stock for as long as 6 months. Its a flat top piston and fairly heavy. The Wisecos that RPM has custom made are likely to be in stock and RPM is a stable company, however the pistons are fairly expensive at $160
Generally speaking as the bore size is increased the peak rpm drops but the torque peak increases but at a lower rpm. The 133 is AMA legal for the modified amateur classes and is the most cost effective choice.
Good luck
 
Joined
Feb 25, 2001
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#4
hey troy, i went with the RPM 139 kit on my 00' and love it. the only thing i didnt like was the price $700+. RPM claims that he will stock the wiseco piston for that kit for many years. dont go with any of these companies that want to sleeve it.BLAH!!! RPM did a great job but is expensive. eric also does some "really"fine work and is alot cheaper.
 
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Joined
Jul 6, 2001
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#5
hey about that 139 kit

so u got a 139 what do u notice in the power range the most like bottom end or top end or both? and is ure bike just as reliable as it was before or do u have to change your top end alot more than usual since you would be running a lot more compression with a bigger pistion and what does a piston cost ya for a piston and ring? and did they re nickacel it when they bored it out or what did they do when u sent them your cylinder? plus could u give me a phone number or something to there so i can see what i am getting myself into or just give me some of your information on what u think about it is it really worth it or not? u tell me cause u have it and i dont but i would like to do it this winter or sometime for the rest of the summer that is left? thanx alot for all of your time
 
Joined
Aug 7, 2001
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#6
If I were you I would check out Eric Gorrs site - He will do the 144 for $375 and he is highly recommended by everyone I talk to.

With the bigger bore kit your bike would end up being more reliable since the power comes in at a lower RPM so You don't have to spin the engine to the moon.

Check out:
http://www.eric-gorr.com/services/cylrebuild.html