Tech Tip: Two-Stroke Top End Rebuild YZ125 - MotoUSA

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.
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[@ehd1990]

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!

[@natelax45]

Edwin D did you put oil on the piston and cylinder when you did it ? Thinking about doing mine and it doesn’t look that hard

[@ehd1990]

@@natelax45 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.

[@natelax45]

Edwin D thanks man, I’ve never done any work on a dirt bike like this before really, but it just seems to easy not to try!

[@ehd1990]

@@natelax45 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

[@renevillarreal4807]

Hey Edwin should I hone the top end on my rebuild?

[@matiasdun6599]

I still miss you, Motorcycle USA

[@REKLUSE53]

A tip for the torque wrench extension method. No formula required if the extension is at a 90 degree angle to the handle instead of 180.

[@sivvinod3187]

What happened to you guys? Your reviews were gold!

[@youtubechangedmyname]

First thing , wash the damn bike. Guy has sand sitting next to a open engine 🙄

[@CarsnStuff]

Such an awesome video. I love watching stuff like this. miss 2 strokes. I really wanna get a cr250 !

[@sherwinphillips3362]

Review Guy love

[@Sabian-]

"thats about as small as they come..... actually they come smaller." lol'd

[@Lowkey_DeAndre]

Whether it’s torqued to OEM spec or cross threaded tight is tight 🤷🏽‍♂️🤷🏽‍♂️🤷🏽‍♂️😂

[@lilmarkbigs]

It tight when it doesn’t get no tighter😂

[@danny12threes6]

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.

[@MemeRider]

"Long overdue for a top end" 2015..... I got a 1993 that's never been rebuilt.

[@jmbraap3822]

Well the new bikes r made of plastic sooo

[@youtubechangedmyname]

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.

[@kyb4206]

@@brandoncallioux9030 i have a 78 Kx never had a oil change and she still a winner

[@Bananahammock88]

@@kyb4206 well that's pretty dumb

[@alexpearson7693]

Don’t forget to leave the rag in the lock. It helps keep it clean

[@martybass9727]

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!💯💯💯💯👍👍👍👍

[@Motorider115]

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

[@rickeyaycock5254]

can you tell me more about this

[@TS50ER]

Replace the top-end bearings every time as well. They are not expensive!

[@alfred7136]

+TS50ER I agree, can prevent allot of trouble.

[@hayleighjackson9050]

Y7

[@kevinstearns4198]

fukin rite!!!!!!!!!!!!!!!

[@sciewter]

Normally I would assume he did but did not say. Those roller bearings do not give you much of a warning.

[@Triumph2004]

Why don't piston kits come with new small end bearing?

[@jefob]

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.

[@dny9394]

It only goes in one way, there's a locating pin so ?

[@johnnelson3339]

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.

[@MsAbanob1]

This is the best video I ever seen on rebuilding a top end

[@MASincorporated]

The noob Mechanic ur profile picture is my screen saver

[@wazzup2987]

This video is so helpful! Thank you so much!

[@kevinstearns4198]

wossner piston and rings and oem gaskets are the way to go.

[@GNX157]

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.

[@dny9394]

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?

[@sawyerwallace9631]

If you use the crows foot at a 90° to the torque wrench it’s the same torque as normal if you use a crows foot.

[@patledgard3518]

Great rebuild video thanks for putting this up would love to see more tech tips from you guys.

[@ngurahpratyusadharmacretry779]

how are you motoUSA?? Long time no see :(

[@ManuelTorres-qy8op]

Thanks I just did mine for the 1st time your video was helpful.

[@marklowe7431]

Take seat and tank off then wash bike. Lot of criticism on this thread but the video was very well done and all the tips dead right. Maybe people being ungrateful is the real prob.

[@ukdashcamz3580]

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.

[@rowena490]

Measure ring end gap, measure piston to wall. If everything's good they go right back in.

[@Gavyn307]

Rowan Cranston yes. But i mean if you already have it apart, a piston is like 100 dollars so id throw a new one in while im at it, just my opinion.

[@glockdude5472]

Always replace it , it could eventually go and scratch the cylinder wall (sleeve). It's just not worth skimping on imo and in my experience.

[@sciewter]

If the ring is worn out your piston is not far behind.

[@RelentlessCo]

I'm confident on everything but the power valve linkage

[@marcokornfeld3445]

bottom end contaminated with dirt , dyno test without an escape system for fumes. Great job!!!!!

[@PvTNuclear]

Marco Kornfeld people like you make me hate youtube, always criticizing others work when you probably havn't worked on a bike in your life

[@Community-Action]

A little dirt won’t hurt

[@jordan_bmx6440]

is that the last fuck?

[@vance12341234]

Exactly what I wanted to see. Great vid. Thanks

[@Knights2theEnd]

I can't believe you took apart the bike with a pile of dirt millimeters from getting inside.

[@mareksumguy1887]

+Knights2theEnd i know... what a dumbass.

[@jonnoMoto]

+Knights2theEnd Meh, it's the crap above that's worrying.

[@564Alanguiver]

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...

[@rexburn1955]

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!!!

[@mikebrown41182]

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?

[@upinsmokelol5759]

brilliant video,plz do a two stroke bottom end rebuild video would be much appreciated :)

[@seanmarino3944]

where did you guys go.. 😢

[@TeeOna2Stroke]

rip

[@conorhutch5168]

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

[@iracingrookie3301]

Depends how much the owner was willing to spend I suppose..

[@mareksumguy1887]

Conor Hutch you have to understand that it is nikasil. You need a special diamond hone. Also, the piston and ring(s) wear before the crosshatch does.

[@rideordiegoonies3471]

because you don't wanna destroy the cross hatching on your cylinder

[@mike300406]

blk plug wasn't ridin hard enough

[@christophermoore1998]

mike carr

[@A_Man_Of_Culture_]

Haven't posted a video in four months, I wonder what happened.

[@matteo.bassini5819]

The organization got shut down.

[@SOLDOZER]

Drug lords killed them.

[@cl1514]

well it’s been 4 years i don’t think there coming back

[@herbrachel9707]

Fine job. Very good instruction too

[@ripmax333]

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?

[@quincythomas3749]

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

[@ogbobbyjohnson7144]

lol

[@ryanlester761]

You don't souble-check the ring gap on the new ring before installing?

[@Theprimalcode]

Do you have a link to the spanner that connects to the ratchet?

[@JakeSmith-pr9wm]

Great video except for the fact you forgot to mention how to install the final Sirclip which is the most difficult part.

[@austinbirchall3857]

I have the same bike with the same exhaust system should I rejet it it’s current stock jets and it feels like it has a big before power band

[@TS50ER]

@4:30 Look at all that dirt on the crankcase!

[@martystevens3969]

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?

[@Ricci___]

Very nice and educational video. Thanks!

[@aarongrace2376]

There's no need for a formula you're probably going to mess up doing to get the right torque with an adapter. Just put the adapter at a 90 degree angle and the torque will be correct.

[@human1513]

There is a formula for sure. And it does affect the torque. Important always but especially with soft aluminum.

[@BourbonwiththeBoys]

should you lubricate the piston

[@ultimatefriikki]

and the cylinder

[@nikosniklapolis6093]

yes always put a lot of oil around the cilinder so when you start it it doesnt get seized

[@rexburn1955]

+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.

[@Community-Action]

She likes it lubed!!

[@human1513]

Can use assembly lube or the 2 srtoke pre-mix oil it will be running with. Apply a thin film with your finger tip.

[@bensnyder3239]

Could you list the tools especially the size t handle for bolts?

[@aklaunch]

Did you put oil on the outside of the piston or on the cylinder walls? I have been seeing mixed reviews on this for piston ring break in.

[@Rabbydabbydoo]

Great video. Not the usual video with techno or metal music crap :)

[@bryce099]

So where is the best place to get gasket kits

[@therealakalaska9485]

note to self and everyone out there... WASH THE FUCK OUT OF YOUR BIKE BE 4YOU TAKE TO MOTOR APART

[@RelentlessCo]

4:25 that marking or it looks like scrapping against the walls there is that okay or normal ?

[@terryfonz4603]

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]

Yamaha has for decades.

[@mareksumguy1887]

@@2DclanSnipingTeam ... has what for decades??

[@2DclanSnipingTeam]

@@mareksumguy1887 , A cylinder size stamp.

[@mareksumguy1887]

@@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.

[@2DclanSnipingTeam]

@@mareksumguy1887 , Read a service manual, Einstein.

[@EmpoTay]

Any videos on how to rebuild top end on 2013 kx250f

[@andrewevergreen9103]

thanks! video about jetting for high altitude riding here in california?

[@wyattlarson1104]

thanks for the awesome video and detail

[@fernandofernandez5719]

Everybody is a mechanic here ...dont understand why you guys are watching

[@maxdad05]

I just found it odd that he talked about cylinder scoring due to not letting the bike get up to temp, yet on the dyno, the bike sounded cold

[@gtrsquadboii3912]

I have a 93 that needs new cylinder and piston and I'm trying to go cheap as possible any recommendations??

[@AverageDaveVideos]

Great video, I was curious how this was done.

[@justinscott3999]

Good demonstration

[@mareksumguy1887]

Make sure you spill a whole bunch of coolant INTO your crankcase!! 🤦

[@cassiusashby28]

+Marek Sumguy .both of yous shut up

[@Damascus..]

ok i did what next

[@mareksumguy1887]

M.F.D Entertainment next, tip your bike upside down to get the coolant out.

[@Sunrisecycles]

why are you torqueing the base nuts that way? do you know how a torque wrench works?

[@adalbertosa8302]

you did it very well. thanks

[@clarkfishingride2499]

Hello sir, where can we order YZ125 fairings in reasonable price? Watching here from Philippines

[@newagemuscle2010ss]

Great video!

[@Mr.Stroke0331]

How many hours was on that piston?

[@79brumley]

Excellent Video.

[@kellyronaghan5587]

1:02 is me after a night of drinking lol

[@daytonkarlson9181]

2015 good end rebuild made 4 years ago problems about 60 hours on it still says long overdue

[@abcdabcd8970]

why you didn't put oil on piston?

[@Community-Action]

abcd abcd- that’s what she said

[@rickeyaycock5254]

Thank you for the info

[@aaronyork6173]

What kind of 2 cycle oil were you using?

[@upinsmoketd_2359]

Passing a honer through the cylinder isn’t recommended before installing new piston ?

[@MaliciousSRT]

Its a 2015 not a 1995, cylinder was fine

[@nmdtruckey2107]

Is it for sale?

[@mudpro200]

what should be the break in procedure for this 2 stroke?

[@SoldierDemps]

How much wed it cost me for one of these? To get done for me?

[@andyjonson9760]

What was that you measured in the cylinder? A ring of some sort. I've never seen that in a cylinder!

[@GNX157]

Andy Jonson that was the rings old and new he had down in there measuring with a feeler gauge. Use the piston to push it down in there so it's perpendicular to the bore. Measure at several locations along the path the ring travels.

[@alexmh6131]

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.

[@dny9394]

Make sure you clean the Power Valve.

[@garytauber430]

loved watching this video very interesting

[@rylanjones5813]

If you put the adapter at a 90* angle to the right of the head of the torque wrench you dont have to use the formula

[@dracgotbands]

I ride 4 strokes and always will but 2 strokes look easy as fuck to rebuild

[@SONICBOOM-117]

Can this go for 2 stroke race go kart engines such as the iame x30 125cc 6spd?

[@alienxyt]

How do you know when you should rebuild the top-end??

[@alienxyt]

No answer. I'm guessing that most people do it by number of hours or compression results. I don't know either of those things for my bike so I am going to try to get through this season and do it.

[@dny9394]

Check your manual. Usually 6 hours for piston & ring change. 10 hours cylinder.

[@2wheelpeel664]

Compression reading before and after ?

[@Ayeecole]

my power valve arm is not lining up is it bent or something

[@MrDrSirGuyManJr]

Anyone know how necessary that power valve linkage spacer is? I lost it but it doesn’t look like it actually needs it.

[@thecrazymanfromireland]

Super video thanks for sharing

[@Aprilpergar1975]

I can never get the ring to stay in place... any tips?

[@Alfsp1]

Don’t you need the hone a tad the cylinder ?

[@CR-rb2sr]

No thread lock for the cylinder jug?? Should you use it or not?

[@dny9394]

Opinion varies. I do.

[@brianbranna9528]

Great video

[@treverricketts9906]

About how much torque were u using when you torqued everything down?

[@seancranger3879]

it's different for every bike look in your bike's service manual or whatever to see the torque specs

[@dny9394]

around 25Nm in 3 stages. I usually go 4 stages: nip, snug, tight, solid.

[@hitthatsubscribe]

Anyone know how long this will take first time rebuilding a top end

[@johnathanhimka]

Where did you get the piston?

[@josemhs1213]

Did this website die?

[@the_socompsp]

great video guys awesome job!

[@adji28]

I like yz 125😍😍

[@covid8317]

Great content thanks