How To Rebuild the Top End on a Yamaha YZ125 & YZ125X

Rebuilding the top end on your 2-stroke YZ125 may seem like a daunting task but with the right tools and know-how, the job can be done quickly and save you a lot of money over going to a shop. In this video, we show the process of how to properly rebuild the top end on the legendary Yamaha YZ125 2-stroke. This machine is a 2019 model but the steps shown here will work for all newer YZ125 and YZ125X models, from 2005 all the way through 2020.
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[@Bgatz1029]

He has his hand torques really dialed in. Love it

[@andrewtrombley1333]

bout 0.15 ugga duggas there

[@aidanvelthuis1267]

Honestly 2.9 ftlbs is nothing. I’m not breaking a torque wrench out for that😂

[@mozer30]

If You listen closely you can her his wrist click when the correct torque value is reached.

[@herbalchicken]

I don't even own a 2 stroke, but I need to see this.

[@mrmotocross6819]

What you also need is a 2 stroke. I grew up riding 2 strokes. I own a kx450 and a cr250r and the kx is my lazy day bike. The cr250 if alot funner to ride and takes more technique.

[@romanatlol]

Love that I’m watching this even though I don’t have a yz love watching it though

[@joedirt9830]

Thanks for the video. I could not do a top end with out it. Keep up the good work.

[@AlexxMarssh]

hilarious i bought top end kit from you guys and did this yesterday great stuff

[@bird4dbk420]

Same here! 😂

[@mattandkatchristie2552]

The power valve cleaning is like open heart surgery jeez doc good job

[@hphillips7425]

Good video. I have never done a top end but as good as the video is I would tackle this job.

[@vince5946]

Another great vid! you're inspiring me to do another build:)

[@elongenjones7270]

Wow. Awesome how to video. I want to see more.

[@tbgtbg6311]

Makes me miss the 80's

[@atuhumuzakenneth8129]

So clean video, love 😍 it

[@jobmxjojo]

This is gold!

[@kensmith9334]

Great video!! :)

[@KimChoonSam]

Watched the video very well. If you see signs of coolant flow, check the level as you saw in the video. I stand on a stainless steel ruler and shine a cell phone flash on the back. It's normal if you can't see the light.

[@panic-revv85]

I've always heard not to use a dingle ball hone on a 2t as it will chamfer the ports?

[@takeiteasy9019]

Would love to see a complete guide on a yzf450/wrf450 as u have done with the yz's

[@takeiteasy9019]

I do see u have a rebuild video on them 7 years ago but would really love a updated version on the new 2021

[@javinlarsen6760]

Old video but only thing I noticed is when you went to file the rings you filed towards the outside, supposed to file toward the inside of the ring so it doesn’t create a sharp edge going against the cylinder wall.

[@rmatvmc]

Good point! I wasn't really trying to take material since we were in spec, and just trying to get the general point across. Regardless of direction I always clean up the ends when done. But yes, normally I would try to file in the other direction. We'll specify that in future videos. Thanks! -Charles

[@mixtips637]

I can't wait to get a 2 stroke to rebuild getting tired of 4

[@gtmnicko]

With the 2001 yz125 power valve linkage does it have a retaining plate on top or just the linkage and screw going in to it ?

[@daryleduardo7055]

What about power valve adjustment? Or are they not adjustable?

[@mickelrosado84]

Where can I get that wrench you used for the inside cylinder nut for torque spec

[@bikerdude6119]

Just bought a bunch of stuff to rebuild my 2019. Man i love shopping at rmatv!

[@rmatvmc]

Heck yeah! We love it too! How many hours on your current top end? - Wes

[@bikerdude6119]

@@rmatvmc 42 hours lol once im in there ,im going to look for signs of wear and take note of what is next

[@dhananjayabandara96]

👍 good job thankyou ❤👍😊🇱🇰🇱🇰🇱🇰🇱🇰🇱🇰🇱🇰🇱🇰🇱🇰🇱🇰🇱🇰🇱🇰

[@jeffgoetz7919]

Charles is the best

[@juliandanielframe4311]

i ride a 1993 kx125 could this help a little?

[@BigElly12]

This looks way easier than I thought it would be lol

[@trentonrobinson2745]

Did you drill those holes on that piston for the exhuast bridge or did it come that way

[@awesomecooly123]

Some come pre drilled others don't

[@mylescheney5583]

I am currently changing my piston lest time I rode I though my bike was lacking power as I was out ran by a 125 and realised one of the pins on my power valves was missing 😂😭

[@DADSGETNDOWN]

Heat Cycle Break in, then go ride normal? I always heard heat/Cool Down cycle, ride for 20 or 30 minutes without going passed about half throttle and without quick revs etc, then put about 3 or 4 hours on it before you really open it up. Ofcourse not only is that what I was told by a few shops but that is for much older bikes too.

[@mattharrell4]

Yeah I feel like everyone has a different take on this. I’ve done a few top/bottom rebuilds and just ride it normally for the first ride. I’ll do a nice slow warm up and then try to give it about 3/4 throttle to help put some pressure on the rings and help seat them. I’d would bet that as long as you don’t run the piss out of it you’ll be fine.

[@boostedpleasure]

I bought a 21 yz250x heat cycled then did a 15 minute low to mid rpm break in ride. After that it was straight to the race track. As of today it has 16 hours all race time. No issues.

[@DADSGETNDOWN]

@@boostedpleasure I ride my little CR80 for 3 years on trails, hills etc Hallin butt everywhere, not one issue, but did top end anyway.

[@JAMES.111]

WOW

[@nicolo2911]

is it necessary to respect a certain gap for the piston ring? If so, how high did you set it? thank you

[@rmatvmc]

Piston ring end gap is definitely a good thing to check. We have an older video showing how to measure piston ring end gap and adjust it if needed. You can check that video out here: kzbin.info/www/bejne/m5bPmqSYn5p3nbM

[@Grimmi112]

He did. ist at 11:57?

[@ianheimaster7390]

Can you do an rm85 next

[@bryce099]

Literally the same thing

[@humbertoexotic8673]

Y’all should make more warrior 350 vids

[@ronk6073]

Why on earth would you hone a nickel plated cylinder anyway? The plating is designed to resist wear from the piston and ring, what would be the benefit of purposely wearing the plating? Nothing under that plating but aluminum... Good luck if you wear down to that!

[@Shadow0fd3ath24]

I always replace those stupid phillips head screws with regular bolts. Lot less chance of stripping them

[@natetwarog1938]

How do you know which piston size to buy? Size B, C, ect.

[@owens5283]

Back of the cylinder had a letter on it

[@owens5283]

Has

[@Redheadrider449]

I have a 2002 yz125 and after I do a rebuild do I have to change the oil gas ratio for the break in period. Thanks very much

[@WM_official]

How often need to do it just for casual riding?

[@rmatvmc]

Follow the schedule in your service manual and do a regular compression inspection. It's better to regularly rebuild the top end in order to prevent the bigger and more expensive repairs. - Wes

[@xxgalaxymast3r421]

do u have to have the torque foot pounds at the right foot pound or whatever or can u just put it on like a regular bolt?

[@harpermx2962]

Just look up the torque specs in ur owners manual u don’t need the torque specs for everything but any motor work u do it will keep ur bike running better and longer

[@austinhoffa99]

How tight do you get the dowel rods ?

[@bradleyforsyth5032]

Can you guys do a clutch on xr600

[@devinn5306]

That took me 8 hours

[@ABM-BJ]

❤❤

[@Jtraceur5]

If I'm getting a new cylinder, do I even need to mess with the power valves?

[@kylebeach2316]

If theirs damage or signs of wear and tear then yes replace it

[@julianlaustsen1991]

ur supposed to measure if the cylinder is oval and taper and the max diameter.

[@dustin9035]

Did I miss checking the valve clearance and lash?

[@rmatvmc]

No you didn't miss anything, that's an adjustment for 4-strokes. If you are joking with me, the comedy club has open mic night on Mondays at 7:00.... 😂 Either way I hoped this helped. Thanks for the support and let me know if you have any other questions! -Charles

[@jermained9874]

Can I have a 1994 yz 250 body and build a newer motor it it such as 2017 yz motor

[@mozer30]

Great video but I think you missed a couple of very important parts. 1. Unless the engine is on the first piston change you should always have the cylinder measured to ensure you purchase the correct piston size. Using a stock piston size on a worn cylinder is bad practice and defeats the purpose, as the piston to cylinder clearance may be at the service limit. 2. I’m shocked that the squish clearance was not checked, nor demonstrated. This is absolutely critical part of the rebuild, as too greater clearance will cause far from optimum performance, yet too tight squish clearance will cause detonation, resulting in piston, cylinder, and head damage in no time at all.

[@Shadow0fd3ath24]

When doing a stock size piston in a stock engine means you don't need to check squish. it stays exactly the same. That is a completely bogus and stupid myth

[@redtobertshateshandles]

@@Shadow0fd3ath24 just compare the two pistons side by side. You should do this anyway, regardless of squish.

[@Shadow0fd3ath24]

@@redtobertshateshandles of it's a stock piston theres nothing to compare🤦‍♂️

[@Pumpkineater19]

Nerd stuff

[@lucianoferreiradesa]

👏👏👏👏🖤🙌🇧🇷

[@charsiewestcott6419]

You were a bit blase` about the description of using the mid driven 12mm spanner with the torque wrench. I presume 22ftb at 90 degree but use formulae when using spanner in the straight orientation. Please be specific in future, you can confuse people inadvertently.

[@redtobertshateshandles]

I use EP transmission lube for assembly, I'm stingy.

[@jonthelamb4549]

I watched this then blew my bike up the next day

[@Wow_nugs]

bad dont even have a bike