2004 YZ 125 Top End Rebuild questions...

9 replies to this topic

Posted May 03, 2009 - 02:35 PM


So I got an 04 YZ 125 a month or two back. I have mainly been setting up the suspension since the engine seemed strong. Raced in a Grand Prix last weekend and the suspension tore me a new one! Gold Vales on the way. Anyway I put some new tires on, chain, sprockets and it is coming together nicely. I planned on putting in a new top end soon but I was going to wait til after the next race next weekend. I was putting in a new plug and decided to check the compression. 75psi! I couldn't believe it. Needless to say I immediately tore the top end off and ordered a new piston kit. Powervalve had a lot of oil in it but everything looked great. It felt so strong I can only imagine how the Wiseco will feel. I THINK the head torques 20lbs and the cylinder 22lbs. My question is how are you supposed to torque the cylinder bolts? 2 of them are no problem but the other 2 I can only get a box end over. I plan on torquing those 2 by feel unless someone has a solution. I am really loving this bike and once the forks get sorted out I will be relieved.

  • rdrata

Posted May 03, 2009 - 03:57 PM


Check motion pro, they have a wrench w/ a slot for your torque wrench to tighten to spec.


Posted May 05, 2009 - 06:20 PM


Ok something is wrong. I put the new Wiseco in and it runs great. Heck I thought it ran great with OEM piston and 75 psi compression (I didn't think it would even start that low). Checked compression with new top end and it's 90 psi. What the eff? Does it need to go through a few heat cycles? Cylinder looked perfect with nice cross hatching. Or maybe my el-cheapo Harbor Freight compression tester is not too accurate. Ideas?

  • Motocross26

Posted May 06, 2009 - 09:47 AM


Are you testing with the throttle wide open?


Posted May 06, 2009 - 11:39 AM


Yah throttle wide open kicking till it won't go any higher. I think I need to check my gauge against another one.

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  • CV4

Posted May 06, 2009 - 12:38 PM


Your gauge is screwed. You should be in the 170lbs + range.

  • petersencollin

Posted May 07, 2009 - 02:10 PM


I have 115 and troubles with starting. Do I need to rebuild it? Any special tools needed? How much money? 2004 yz 125


Posted May 07, 2009 - 02:53 PM


I would try the leak down tester kit that accu-products.com sales but they are 2 stroke street bike related YZ 125 motor is similar to the TZ 125. They also have this neat lil circlip installer tool I want.


Posted May 07, 2009 - 05:15 PM


I have 115 and troubles with starting. Do I need to rebuild it? Any special tools needed? How much money? 2004 yz 125

You can find it a little cheaper on eBay but I got a Wiseco with all gaskets and bearings and 24 hr shipping for $130. You will need a torque wrench. Good price here on the TT store too I bet...

  • petersencollin

Posted May 08, 2009 - 12:45 AM


Thanks guys

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