MotoUSA shows you how to rebuild the top end on a YZ125 two-stroke. We used a Vertex piston and Cometic gaskets. Always check your owners manual for proper torque specs. Subscribe: ru-vid.com_... Website: www.motorcycle-usa.com
i used this video to replace the piston on a 2004 yz125. im mechanically inclined but have never been confident with getting into motors. this video helped me get passed that and now the bike runs 100% better. just wanted to say thanks!
@@nathanmachado9412 my father in law did. i didnt want to but he decided to do it anyways and he applied a good amount. bike runs great. we used a wiseco piston kit that we got for 120. we also purchased the torque wrench tool he mentioned in the video, got it on amazon for 12 bucks. it was really an easy rebuild.
@@nathanmachado9412 no problem man. on the 04, the torque values were 22 ft lbs for the cylinder and 20 ft lbs for the head. good luck if you decide to do it. message me if you have more questions
Just because it's never been rebuilt and still runs, doesn't mean it wouldn't benefit from a new top end. Also if you always putt around like a Grandpa then ya no shit. Try opening the throttle. I use to rebuild my YZ 125 every 10 races. I knew guys that did it every 3. Riding around your lawn for 20 years isn't riding.
I absolutely love yall!Yall explain perfectly how to fix bikes and I've that!Without yall on fixen bikes idk were I would start keep up the great videos!💯💯💯💯👍👍👍👍
good video for someone that doesn't ride 2 strokes but thinking of buying one in the future. The word rebuild kinda scared me whenever I'd hear you have to rebuild around 20 hrs or so for 2 strokes. But I have to say, the dirt that was centimeters from the inside of the engine was driving me crazy. Especially when you have a really clean shop and environment it would be best to make an instructional video with actually cleaning around the areas that are vulnerable to dirt or friction. My OCD was off the charts at the moment. but thanks for the video very helpful and now I know i'm capable of doing this in my own garage.
Awesome video, only thing i didn't see explained was why rings need to be positioned properly so they don't pick up on a port. everything else was spot on.
dont forget to put a taper on the exhaust bridge port holes on the piston, the oil will sit in there and prevent the exhaust bridge from wearing out as quick, learned that some someone that won the yamaha tech gp 2 years as well as many many things
when i know im gonna do a top end i clean the bike with the expansion chamber and muffler off the bike and stick the exhaust bung up the port to stop water, its the only way to get that tricky spot on yz's...
Dirty ass environment, and Oem parts are by far the best for Yamaha motors. You didn't hone the cylinder dumbass, how's the rings supposed to seat lol, and you didn't oil the piston skirts either, I know they are teflon coated. But still, and for teaching reasons this video is horrible! FAIL!!!
oem parts is the best for yamaha motors. Do you have anything to back that up? Aftermarket pistons are often made to higher tolerance than standard oem and it depends on what kind of performance you want out of your engine or how it is tuned?
Looking at the plug I don't think will give any indication of jetting at this point. Who knows how the engine was run for the last minute before shut down? You've gotta do a full throttle run and do an immediate shut down without idling then pull the plug and look at it. The other thing I noticed was, not much was spoken about looking at the top of the cylinder for a possible ring ridge developing, where the ring wear stops before the end of the cylinder. A new ring may hit that ridge and crack or cause other issues.
Good points and when does a top-end not include the Power Valve? They can cause a World of Hurt when they go wrong, and they do. Usually they are full of tar which glues everything together. Next time ok?
If im ever fortunate to get back into moto x again i think id go 2 stroke. I actually prefer the more predictable instant powerband on a 4 but im fairly confident i could rebuild a 2 stroke and with a 4 i would not have a clue. Im surprised how simple that looked on the video.
This is a very informative video. My son and I used it to successfully do the rebuild. You'll need a specialty tool for the torque as well as a torque wrench. If you intend to maintain a bike you should own those inexpensive tools anyway. Takes significantly more time than shown for rookies to complete. Take the extra time and clean things up real well. Make sure the head is flat before re-installation. Pay a pro for honing if necessary. The t-handle tools speed things up a bunch. Buy some and have fun. This project is not for a first timer - you'll need some mechanical know how.
so here's my question, lets say you pulled out the old piston and start to take measurements and check what piston you need A,B, C Whatever. you get a new piston and check the piston ring gap inside the bore. if the gap it's not within spec, what your suppose to do?
You should've put oil on the piston and cylinder. before installing them. There is a 2 cycle ring compressor set with a base adapter but that cyl. obviously had a taper at the bottom of the cylinder. If you could, maybe install oversize rings. I put .030 rings on or car and filed them to minimum gap- .008- .010 spec. I filed them to .008. It WORKED!! Why does it smoke? Maybe cylinder was worn. Always mic. the cyl. What did the owner say?
Can anyone tell me why the cyclinder wasn't honed lightly before the new piston and rings where put in? I always thought you should lightly hone the cyclinder the create the best possible seal for the piston rings
So I'm getting a 2 stroke 125 soon and need to know how often I'll need to. Change the piston. I don't think letting it go till it locks up is the best idea
+Nicolas Cools you don't want to put too much oil on the cylinder buddy. the rings have a harder time seating. if it's over oiled the rings "float on the oil" and won't contact the cylinder wall enough to break in. just a thin layer works well. and oil the piston skirts a little too. and the crank and wrist pin bearing obviously.
What do you mean the cylinder has a letter on it??? That size piston is for wear when a cylinder gets old you use the CD piston to bring the clearances back into speck. New cylinders get AB pistons. Why would you send people searching the cylinder for a letter indicating what size cylinder it is????? Ive never seen a size indicator on a cylinder.
@@2DclanSnipingTeam oh really??... Yamaha have such poor manufacturing quality that they can’t even maintain the same dimension spec for their cylinders!? 🙄 you talk absolute nonsense.
wow is it really this simple? I've got a full rebuild to do on a RS 125, was gunna get a friend to do it but I might just do it myself. the top end any way.
