How To Rebuild the Top End on a Yamaha YZ250 & YZ250X

Shop Now | Yamaha YZ250 Engine Rebuild www.rockymountainatvmc.com/Sa...
Whether it's because of excessive noise or just wanting to refresh your engine for the riding season, rebuilding your top end is a great way to get familiar with your bike and prevent more catastrophic failures in the future. Knowing how to do the job correctly will save you tons of time and money compared to taking it to a shop as well. In this video, Charles shows how to rebuild the top end on a 2009 Yamaha YZ250, but this process will be very similar for Yamaha YZ250X engine's as well.
Watch Next:
Yamaha YZ250 & YZ250X Bottom End Rebuild | Part 1: Engine Disassembly
• Yamaha YZ250 & YZ250X ...
Yamaha YZ250 & YZ250X Bottom End Rebuild | Part 2: Engine Assembly
• Yamaha YZ250 & YZ250X ...
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[@EarthSurferUSA]

Different pro engine builders have different techniques. I have not listened to the vid from this retail guy yet, but I will chime in below if I disagree and why. :) 1) A compression check is only good if you have an accurate tester, or know how much it is off. Many testers are "under inflated". If you check ring end gap, cylinder roundness and have good plating still, (and run at 32:1 oil/gas), and all is good, you will have good compression. If you tear down your top end and find the ring end gap is still good, you can wait longer for maintenance intervals, and even calculate it based on the wear you have. 2) The "snap gauge" is also called a "telescoping gauge" (a type of "comparison gauge" that does not give you numbers, but has to be measured itself by a mic for example). Used correctly, they are accurate enough for this job easily, but not as accurate/repeatable as a good set of inside mics. 3) My Wisco piston kit came with the wrist bearing. Got it less than 3 years ago (after this vid was made). 4) 1:50 Ahh, not using the stock reed block spacer for the V-force reed valve. More powerful. :) 5) If you are replacing the rod and lower bearing, you really don't need the piston wrist pin puller. 6) Upper hanger bracket is called the "head stay". 7) 7:47 I don't think those 2 screws are lock-tighted. Too hot there for lock-tight. It melts. 8) Show us the "carbon remover". 9) You would be surprised how many little vertical scratches you can have in your plating, and still run good. 10) Good cylinder measuring. Did not specify the taper and out of round limit though. Maybe in the owners manual. 11) Personal preference: Oil is in the gas, so the piston will soon have lubrication, so I don't like to use 2-stroke oil on the piston and cylinder. Pro mechanics would even put the piston and ring in dry for practice, (to help seat the rings faster), so it will be ready to race later in that day. I use a "in between" WD40. Great job overall. New guys who follow your steps will do a good job.

[@allenyoungs]

If you turn the adapter for the torque wrench 90 degrees you don’t have to do any correction or math. 👍🏼

[@richardried4197]

Or just use an extension from above

[@ZSharkPH]

This video is gold !!! Thanks Rocky Mtn.

[@user-ls3cj6nr6e]

@10:43 where in you said if you feel any gouge or groove in the nikasil it is an indicator that you should replace it I remember what you said at the Glen Helen 24hour race where you don't expect the backup bike (WR200) to last that long especially with what happened to the bore well anyway that is what is recommended as per manufacturer and I totally get it. I recently rewatched all the cheap bike series and it was all a blast!

[@ericbrandt829]

Great video EXCEPT! If you ever have to file a set of piston rings to increase the end gap....ALWAYS file from outside towards the inside....I cringed when you were pulling the rings on the file...ALWAYS PUSH ONLY....Reason? The rings have a plated outer edge and you can fracture the plating reducing ring seal.....Otherwise great instructions.👍

[@kikorodriguez4046]

Very good into detail video I’m no master mechanic but I blew my yz250 and this was my first time doing a rebuild this video helped out so much highly recommend 10/10

[@jupiterjac6438]

When you have to change the valves and the pistons is that considered a “rebuild”??

[@phillsmith5100]

@@jupiterjac6438 🤦🏼

[@toukebrimehdi525]

Il faire le rodage...

[@JamesDeffenbauggh]

😊​@@jupiterjac6438

[@nicksainders5611]

Thanks for the video ! This helped me tremendously!!

[@ElonMuskX]

I love motion pro tools!!!!!! Make doing things the right way easy!

[@Momfasa]

Nice video! After watching this I know I can do it by myself. Going to order myself a YZ250. First dirtbike. Total noob :)

[@tylerpayne9719]

Great Video! Very informative, Thanks Rocky Mtn!

[@rmatvmc]

You bet!

[@shaunix]

great video, very informative thank you for sharing.

[@nathantrickett3111]

Love your vids! If it wasn't for you guys I would never have bin able to rebuild my 05 crf450r, I watched that rebuild vid and the roached to racing build over 100 times, keep it up!

[@rmatvmc]

That's what we like to hear! Glad the video helped and thanks for watching!

[@kushlord1397]

Yessir

[@redtobertshateshandles]

If you can, buy longer handled spanners/ wrenches, they're easier on the hands. More leverage. Short ones are good for tightening stuff, less chance of stripping threads.

[@r3gaming545]

Could you guys do a video on the top 5 best mods for a Suzuki LT250R?

[@viniciusalmenau8284]

Muito da hora sua explicação sua explicação. I am Brazilian.

[@andreaagnella]

hello do you sell those gas line(those from the tank to the carburetor) on your site? I can't find them, would you give me the link??

[@adampaniczko8198]

Thank have question could you tell me the year of those graphics on the tank thank you

[@jupiterjac6438]

If I get one of these bikes an actual 2004 yz250 For 600$ with the valves and piston messed up would it be a good deal if I took it and replaced the whole cylinder w the piston and power valve? I see some around 600$ for the complete kit. What do you guys think? Let me know your opinions thanks guys

[@waylonlegend4603]

Currently rebuilding an 81 yz250

[@screamingpigs]

very useful thanks!

[@rmatvmc]

Glad it was helpful!

[@vince5946]

Great vid once again, very informative and detailed. P.S. Was that Chase's toothbrush? :)

[@rmatvmc]

I can neither confirm or deny. -Charles

[@robertococcia9815]

Hi man why wiseco piston dont have classic 3 sizes a b c comparison with other brands

[@levibuenamea1779]

Is this as good as the factory engine?

[@williamhall7785]

the taper measurement seems to make sense, however when calculating out of round i would think you stick to the same measurement points (depth in cylinder) when finding the difference between x and y axis. You could potentially have a different measurement for the x axis at one depth, and the y axis at another depth, but still have a cylinder that is perfectly round (the difference being from out of taper)....perfect roundness being possible in this scenario with equal x and y measurements at the two depths being compared.

[@toukebrimehdi525]

القياس من جهة الأعلى فقط .

[@savagebikerx1357]

I installed an oem B kit into my 23 yz250x. The ring gap was .0019. The old rings measured .0028 with almost 300 hrs on them. But the manual says .0037. Im worried that .0019 is too small

[@ronilsonsoares4194]

If replacing the piston for maintenance only, do I need to take apart the power valve and all that?

[@joshuahill573]

No, always good to take apart the power valve and stuff every now and then though.

[@midwest9070]

I noticed in the video you went back with the factory Phillips screws and bolts, what’s your thoughts on using Allen head screws and bolts as long as they are the same thread, width, and length so they’re a lot less likely to strip in future?

[@benthebuilder8853]

That's what I did

[@redtobertshateshandles]

If the heads are fine reuse them. If not replace. Allen bolts can still sieze. Lube the threads.

[@nastysoda9212]

use a JP1, JP2 or JP3 screwdriver, stop using phillips and you won't strip your screws anymore

[@user-qg2hz2nq3r]

Make a video on how to replace a standard hydraulic clutch with a yz 250 / yz250x hydraulic clutch

[@premiumdetail5349]

My yz250x stopped on me like out of nowhere I was ringing it no doubt , and wheel didn’t lock up. But I went to restart it thinking gas ran out , and then it sound like something jumping around inside. And turned off right away 😣 I need help , and I’m tryna get my friend to help me he’s a good car mechanic I’m like bro this stuff simpler.. hopefully he helps me rip it apart and fix it.

[@itsd.k9487]

If you ride for fun and just do enduro type stuff how often should you rebuild your yz 250 ?

[@rmatvmc]

There are a lot of variables that go into how long you can go between top ends but if you aren't racing you should be able to get 50-100 hours on a piston. A great way to know when it's time to replace the top end is doing regular compression tests. We have a great video on that that you can check out here: kzbin.info/www/bejne/q5qVlKl5nqykd5Y

[@NickW90]

I love these rebuild videos you guys do. Any chance you guys could show how to rebuild a 18-21 crf250r top end. There are next to no videos on these new honda engines. Thanks!

[@rmatvmc]

We have it filmed and we're editing it now. Might be a couple of weeks before it drops! -Charles

[@NickW90]

@@rmatvmc sick! Thanks

[@NickW90]

@@rmatvmc any update on that video being released soon?? Thanks

[@jason8984]

I just bought a 03 yz250 but it's seized so wish me luck I'm ready to rip

[@niick8145]

I got a question . Does the transmission oil and crank oil share the same oil or is it separate. I was looking for a drain plug for the crank but there is only for the transmission. I had to flip the bike to train from the crank.

[@NickW90]

The engine oil is the oil you mix with the gas. Transmission oil only does transmission and clutch. There is no filter for your transmission oil so change it often

[@mc9304]

What? There was oil in the crank case?

[@NickW90]

Any update on the 18-21 crf250r top end video you said you guys have?

[@rmatvmc]

Yeah, we have it all edited and it should go live this week. -Charles

[@NickW90]

@@rmatvmc right on thanks man

[@shakoiatenhawithacrossjaco9051]

How to rebuild a 2 stroke top end. Remove cylinder head. Take off and replace piston. Put head back on. Finished. That’s why I love 2 strokes

[@rmatvmc]

Simple and easy to work on! 👏👏👏

[@Liliros]

Hello, I have mounted a fatty and shorty fmf exhaust on my yz 250 23, my question is is it protected with the 50 n3ew pos 2 series carburetion and 178 main jet, or should it go up to 180, thanks in advance

[@rmatvmc]

It should be safe to run with that jetting. It really depends on elevation and temperature, as well as intended use (sandy hills etc.). I know that people have had good luck at sea level, 70-85 degrees, 32:1 premix ratio, with a 175 main, 48 pilot, N3EW needle 2nd position, and 1 turn out on the air screw. You might want to make adjustments from there. If you do, try one jet size at a time till it runs the best, then check your spark plug. Look at the porcelain by the center electrode. Ideally you would want that to be brown, black is rich, and white is too lean. Look up "plug chop" if you need more information.

[@Liliros]

@@rmatvmc Thank you very much, I will do some tests and look at the spark plug, good morning

[@EarthSurferUSA]

@@Liliros Here is how I jet a stock 2-stroke with a carb. They always come from the factory set rich, to be safe in any air quality around the world. So if you are riding on a track (not wide open all the time), and your "correct" plug is dark, I start by dropping the needle one notch, (move the little c-clip on the needle up one notch.). One notch is a big jump, and it will clean up the plug and you will feel more mid range power with less/no drool out of the pipe of vent tube, also keeping your exhaust power valve cleaner for longer. The YZ is very rich, but if you think it is too lean in the middle, you can get little washers (or make them), to punt under the little needle clip, so you can drop the needle a half, or 3/4 notch for example. Once you have the middle cleaned up, you will use full throttle runs, up a hill (the more load the better, and a cooler day helps keep you on the safe side of ambient temps), to check the main jet. Make sure you are on the rich side for full throttle runs (and stock jetting should be, but may not be with come engine mods), with a dark plug. Them hammer it wide open up a hil for 30 seconds, and hit the kill switch (so lower rpm's don't darken the plug. Just check full throttle for the main jet). If the plug is darker than a light brown and a dry electrode, put in the next smaller main jet and test up the hill again. I have never had to mess with the pilot jet, (idle to /8 throttle opening) on a stock carb. after setting the needle and main jet. Now, the plug should be a light brown color, with a dry electrode and even some color change to a bit darker at the elbow of the bent electrode. The bike will no longer drool out of exhaust exits, it will pretty only smoke on start up for quick spell, the power valve will stay more clean, less sticky, and you will have gained about 2hp with more power across the usable curve and have a higher top rpm. If the plug turns grey or white, you went too far. Drop it in the middle, then test for the main jet works pretty good. I just suggest a colder day (more oxygen) and a good load to the engine to do it, and you should stay on the safe side of too lean for most conditions.

[@EarthSurferUSA]

Also, if you do most nay engine mods or put on after market engine products like a pipe, you should re-jet the carb, especially if you had it set well, (on the edge). I am going to raise compression for one example on my YZ250 2-stroke, (use a older higher compression head, or lower the cylinder a bit), and that will burn better, and probably make the bike run more lean, needing a bit more fuel. You can get that older head (2011 or before I think. look it up), and get a good mid range boost and still run pump gas, or cut .0085" off the gasket surface of your newer low compression head to make it the same as the old one.

[@Liliros]

Thank you very much for your answer, I like to have my 2Ts a little richer, I have decided to mount the 180 main jet in winter without verifying the color of my spark plug

[@wanmuhammadfakhrullahwan8078]

👍👍

[@brendon4901]

How long would you say it would take someone doing this the first time?

[@rmatvmc]

If you have all the parts and tools, you should be able to knock out this job in less than a few hours.

[@brendon4901]

@@rmatvmc Thank you, not bad at all.

[@RideWithTheWolf]

Just get some 220 grit sand paper and sand everything :D

[@craigsteinman9807]

How do you know if you got a ..A B C or D ..cylinder/piston?

[@rmatvmc]

Check the markings and measure them. Did you watch the video? 😅 We show you how right here kzbin.info/www/bejne/nnutfWisndGgg80 -Charles

[@craigsteinman9807]

@@rmatvmc thanks

[@Onewaygoon704]

Are the motors same on 250 wrs?

[@rmatvmc]

I'm not sure what bike you're referring to that is a 250 wrs. But this video will apply for Yamaha YZ250 and YZ250X 2 stroke dirt bikes.

[@Onewaygoon704]

@@rmatvmc ok thx

[@marlondemata3410]

Hi! Can I swap yz250r 2002 block & head to yz250x 2018??

[@zweitaktalteisen1854]

you did forgot to put the springs back in their place on the shaft for the power valves...

[@dnickens20115]

I saw that too...

[@richardried4197]

Look closer, they are there, he just didn't say it.

[@Chase_01]

How many hours was on it

[@rmatvmc]

I'm not sure on the hours, just going in to take care of the problem. -Charles

[@huntereury1585]

Hi

[@user-zc8fm8xd3p]

завёл бы хоть))

[@josephlongo6556]

That’s sleeve in the cylinder not nikasil

[@soxh8ter]

So just take it to a shop then?

[@rmatvmc]

If you don't mind paying more and not have your bike for a while, having a shop do the work is an option.

[@studyobserve1]

I need my 69 dt 250 motor rebuilt

[@rmatvmc]

Even easier! Less parts and air cooled. I don't know if you watched the 5 miles of hell series but Justin rebuilt his DT 175 top end on there and you can see what you'll be getting into. Between these YZ top and bottom end videos and your service manual, you should still be able to get it done no problem. Finding parts might be another story... -Charles

[@toukebrimehdi525]

3 mm

[@dylanmonnelly9539]

I put that spacer on the wrong side of the power valve linkage. F*ck.

[@corumstratton2317]

You didnt measure the squish bro😬

[@EarthSurferUSA]

You don't have to if you are staying with stock parts. The parts stack has tolerance to be wide and safe, but usually run better after you tighten up the squish with mods. After that, you should check the squish if you change any parts that create the squish distance. They don't check squish during assembly at the factory. They know the dimensions and tolerances of the parts, (5 of them that create the squish clearance), and just pick them out of a batch of parts to put together. That is why stock squish is almost always on the wide side, and never too tight.

[@joeyslap426]

I thought 2 strokes were less maintenance than 4 strokes????? What is this nonsense

[@geopioneergsxr5357]

This is a blown engine repair.. Trust me, the work here and the price is like 10 times less than a 4 stroke in the same situation..

[@joeyslap426]

@@geopioneergsxr5357 I know I own both. This video is overkill though. Spray that power valve out with brake clean and keep it moving

[@Cornholio223]

I always thought 2 strokes needed more frequent maintenance but the work is usually cheaper.

[@geopioneergsxr5357]

@@Cornholio223 ALWAYS cheaper.

[@premiumdetail5349]

Lol I love people who speak out 🙌