How to Install a New Top End on a 2 Stroke Dirt Bike • YZ125 Rebuild Ep. 4 • WIN THIS BIKE!!

Install a new piston in your 2 stroke dirt bike by watching this step by step tutorial. It's an easy process to follow so we hope you enjoy the video!
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Disclaimer:
Motorcycle riding is inherently dangerous. This video was filmed on a closed course with a professional rider with years of riding and teaching experience. The Mx Factory and all related personnel are not to be held responsible for any injury resulting from attempting these techniques. The bottom line is wear safety gear, take it slow, have fun, and consult a riding coach when necessary. The bottom bottom line, DON'T BE DUMB.
#dirtbikevideos #dirtbikerebuild #motocrossbike

[@kings17court]

It's mind-blowing how much more simple a 2-stroke is compared to a 4-stroke. Goodness.

[@messiona]

Mind blowing how much more fun too. and cheap

[@classicbikerx3588]

They are just as complex as any other engine type, sometimes more when you get into performance tuning (check out an RD400). Just a ton of steps skipped or not filmed here. Grabbing the connecting rod and wiggling it around is not a measurement...

[@RevolverDennis]

@@classicbikerx3588 have you ever heard of timing maybe? Yea 2 stroke doesnt have that

[@classicbikerx3588]

@@RevolverDennis Not sure about your point. And 2 strokes (older ones) have ignition timing that has to be set with a dial gauge and timing light. So....

[@RevolverDennis]

@@classicbikerx3588 you Said they are as complex as any other engine, they are not, they do not have valves to make up timing with the crank, just insert a new piston and youre good to go, 2 stroke dirt bike over 4 stroke every day of the week but if we talking street bike then i would choose 4 stroke since you dont need to change things more than you drive

[@Mechanimations]

I've not seen a rebuild tutorial that covers the subject so efficiently. Great work, I hope this series takes off for you!

[@kings17court]

'Now it's time to install your shiny new piston, and really let your bike know that it's loved." Love that.

[@knolysjohnson7244]

A series we all can benefit from, Thank you for putting these Rebuild videos out!!

[@zusanlist3623]

Absolutely loving these rebuild tutorials. Thanks for sharing the wisdom.

[@jack_wright_1685]

Thanks, I gotta rebuild mine and this vid was so easy to watch, will def be using it

[@coleyarbrough2319]

Love these videos! They help so much, much appreciated

[@lad63bird]

THE BEST REBUILD VIDEO TO DATE...KEEP IT UP!!! and Thanks!

[@UncD.]

Ik what video I’m using to rebuild my top end… real short and gets to the point, great video 👏🏼

[@caleblafford3820]

Great video guys 😁👍🏼🔥

[@speedyboi349]

Well what can i say he did a perfect tutorial here no doubt about it👍.

[@AndrewBoundy]

Awesome as always.

[@jeremybrown9648]

Freakin solid video. Thanks for the knowledge, you helped me out big time. 🤘

[@kings17court]

Another great video. So appreciated.

[@TheMxFactory]

Thank you for watching!!

[@TheEvilive]

most importantly you always need to check Piston ring end gap. that is the most important step you missed. also use a crowfoot tighten the base nuts for the cylinder....

[@tony9t]

Excellent video.

[@spymaine89]

excellent thank you

[@jimwil6972]

Good work. Build the wall 👍

[@travismcdaneld9656]

Wow! That was easy!

[@HadrienATF]

Not measuring the bore? How do you know you have the right piston to cylinder wall clearance?? That's a pretty important step you forgot to mention... Also ring end gap should be adjusted

[@tylerars24]

x2. I've always been under the impression that checking ring gap was really important.

[@331moto]

Also drilling expansion holes.

[@pasisten8145]

@@tylerars24 I just had a piston and cylinder failure on my son's YZ85 because of a too small ring end gap. Everything is witnessing this, some mechanics have confirmed that. So Yes it is absolute must to check that.

[@FirstGendodgegarage]

Also when he was torquing the bolts he didn’t pat them on the head and say “Well those aren’t going anywhere” I’m concerned they might go somewhere now

[@VibN117]

Man there’s a lot of shit I’ve watched in this video starting with the first half that made me question a lot. Total laziness on this man part and tbh this is why peoples rebuilds last 5 rides now days. Not checking necessary components that work with the piston during a rebuild bc it “feels good” or “the bike has low miles” blah blah. Total bs new bike or an old bike low miles thousands of miles u check any component work with the top end, And if u have to do more work bc of it u call the customer if they don’t want more work u close it up and send it back. U either do it right or not at all. And that’s what’s wrong with people today. I fucking hate it man.

[@gymnetixs4018]

Great video

[@jenrizar660]

Hey brother I got a Polaris 2 stroke and my question is that if the measure of the head is 75mm,the piston kit That I had to order is 75 mm as well? thanks awesome video

[@PowersportsAT]

This video might be the reason I get a 2stroke for my next bike. Engine is way more simple.

[@joeplaugher6405]

hey bro i got a 04 kx 125 got it a year ago i’m about to do a top end rebuild it’s got athena cylinder already hasn’t blown up but can tell it’s probably close would you just buy the 650 dollar kit that comes with everything or just replace the piston an ring i’m asking cuz of the shipping problems lol oh is there a better option then athena thanks

[@Dangerfrass89]

So he didn’t have aa new Wrist pin bearing with his vertex piston as well !! I ordered a Respin Bering From wisco I should be good hey ??

[@groomlake51]

Did you use a Crows foot to torque that cylinder nut in the power valve housing🤨

[@tomasdelasotta4616]

Nice

[@TheMxFactory]

Thanks!

[@Chicomypal]

What is the brand of torque wrench you used in this video?

[@jgbelmont]

What does it mean if I have thick grease and water on my crank and rod?

[@4x4you]

I bought an old yz 125, and turns out it needs a complete engine rebuild, and I have never done something like that so it’s going to be interesting.

[@stephanharlow288]

Can you use pre mix oil to lube the parts

[@Griff.official44]

Is there supposed to be dark oil In the power valve compartment?

[@thethirstymoose]

Yu make it look easy.. im rebuilding a string trimmer, 2 rings...can't get the cylinder on

[@messiona]

3:41 what is the thick o ring in the lower left used for? I’m confused.

[@dpotie]

Where did you get that scrubby pad that attaches to your drill? 0:29

[@Revelation22_5]

Using a Yamaha piston/ring and my ring does not have a T or any markings? Any idea how I know which side goes up?

[@MS215_]

Insane dude!

[@TheMxFactory]

Thanks a lot!!

[@rustcoal]

How do you know what size to get for the new piston

[@masonvohler7998]

My gape in the cerclip is opposing the gap in the piston (4:40) I can’t get my piston off, how do I get that clip out??

[@aarondoyle6610]

Why does nt the new piaton not have. The lube holes and old one does?

[@landontrombley248]

Two strokes are the best

[@daqueztaylore1225]

So easy

[@rockgold9140]

How did u judge the piston size...

[@richiemontanez8340]

Do you got to exit 125 for free

[@331moto]

0:33 Dude is using a torque wrench to remove the nuts... I bet that thing is accurate now....

[@JoranPrins]

but how did you measure the torque for the cylinder nut in the powervalve?

[@haloreach107able]

Joran Prins You don’t, Wing it

[@michaelrebello4918]

special torque tool EDIT: yeah just wing it tho

[@jowens4160]

A crows foot.

[@ktmadventurerider7266]

Top end rebuild parts were just ordered... your video should make it a smooth process (fingers crossed) Where do you get your scotch brite bits? All I can seem to find are flat disks

[@andrewleon2033]

So how did it go?

[@riversmith6382]

@@andrewleon2033 i guess bad lol

[@DIXIEMAFIA251]

Legend has it...He is still Rebuilding lol

[@ktmadventurerider7266]

Sorry, went very well. YZ is still running strong as is the daughter's CR125 that we've done the top end on twice. (She races hare scrambles and beats on hers a bit more)

[@DIXIEMAFIA251]

@@ktmadventurerider7266 Glad to hear that Brother!!

[@SamBrotherman]

Same thing for a yz85?

[@jah-ra3639]

The guy I bought my yz85 from told me to run 32:1 and I got a lot of hour it on it before my top end blew up could this affect the bottom end as well cause the day I got my bike I had to replace the bottom

[@somebodyelse9696]

Jesus man. This comment is one long run on sentence.

[@user-ws9vb8hl6y]

What size is the top end piston?

[@Hi-sp2nw]

What type and mm is this piston

[@Kyle_gallegher]

You didn't need to grind the ring gap?

[@berkutmotovlogs7954]

I wish my CR250 power valve was that simple, that thing is a nightmare to keep track of parts order, especially with all the gunk that gets in there

[@janetyoung3807]

hi

[@Grant-ou5qr]

What year is that yz125

[@50ccAdventure]

Did you torque that head bolt behind the power valve cover??

[@RelentlessCo]

Dan kind of hard to do . Most people I’ve seen just tighten it kinda hard and get a feel . Torue the rest for sure tho o

[@Asylum3D]

@@RelentlessCo I usually put a torque wrench on a socket which is held in a vise. Get the feel for that torque and just apply that kind of force to the bolt. Gets close enough.

[@RexProctor]

I didn't listen and now I have one of the clip things down inside the crank casing

[@dakotahigday4647]

if my gaskets didn’t ship it everything else did could i run my old gaskets for the track day this weekend?

[@fckyoumate620]

I want to know the same

[@JETZcorp]

With the head, if it's an O-ring style head you can probably get away with reusing them IF the O-rings look absolutely flawless. How likely that is after being in service, I don't know. If it's an older type bike with an actual head gasket, you can reuse copper head gaskets but you'll want to re-anneal it. That's not hard, just involves getting it glowing hot; you can look up that process on KZbin. You could get away with not annealing, especially on an air-cooled machine, but anything water cooled and modern probably should be done properly. The base gasket at the bottom of the cylinder is usually paper and usually toast when you take it apart, but it's not very picky. If the old one is torn, you can make one out of any thin cardboard type material. A frozen pizza box or beer/soda carton are great materials for an impromptu base gasket. I know of several bikes that have had Red Baron base gaskets for 10+ years of service.

[@snafuequals]

@@JETZcorp these guys owe you a beer, even if the answer did come 8 months late 😂

[@kiddclofilm]

Simple

[@mixtips637]

I want to rebuild a dirt bike

[@dragoslavpetrovic3616]

Circlip opening must be on up or down position, not on side.

[@jakubj3408]

So i got a fresh rebuild on my kx85 and what i see is coolant coming out of the bolts of the cylinder... any idea why this is ? the bike has around 40 minutes of riding on it

[@_kieranwilliams]

Mine leaks a tiny bit of coolant to

[@faltakktm]

Id doesn't matter if you arw tightening or losening the cylinder head or the rotor etc.. It is the same you can warp it both ways. So crisscross tighten it and crisscross loosen it

[@6henny443]

wrong

[@TheRealCozy]

What piston would you recommend for a 1997 rm125?

[@LimaTangoZulu]

I use Wiseco, I've had good luck with their pistons in my 1997 CR125. But there's a ton of good brands out there.

[@jsned2502]

You have to measure END GAP.

[@bikesanddrums9143]

Skipped the most annoying part, that orange Inner o ring that's always too big. Manual says to use white lithium under it, still a pain! Anyone have any tricks for this issue?

[@tonyzweedyk478]

Always check the reeds, tore down my bike after years of owning it and turns out, it had no reeds!

[@jackpinekid1]

lol

[@gladysaguilar7106]

Where did you order your piston and gasketkit bro?

[@messiona]

Best deal is the complete kit from Athena

[@neogeomedia]

How long does this take real time? I have 2 2-strokes and a 4-stroke that i've never had to rebuild(KDX200,TTR125,PW80)

[@AndrewBoundy]

I did just the head gaskets (not the cyl pull) on my 250EXC - took me 2 hours because I was fussing insanely (I am not at all experienced and this was all new) - I think I could do it again in 30 minutes to be honest - it's a lot about confidence and a little experience. Your 4-S will take a LOT longer than your 2's as it's way more complex.

[@kings17court]

neogeomedia ... that could vary widely, depending on you experience, knowledge, and confidence. People who have done it many times before could just bang it out in no time ... probably 20 or 30 minutes. A tentative newb, who is doing it for the first time might take 2 to 3 hours. I'm a tentative newb, by the way.

[@peytonthomas4506]

i love kdx’s great bikes

[@490Adrian]

I’m too scared to jump to a 2 stroke just because rebuilds would a 250 4 stroke be good instead a 125 2 stroke?

[@Asylum3D]

I have had many 2 strokes & 4 strokes. Both have their things you need to do. Replacing pistons isn't that expensive. You will have expenses with both, but the question you should answer is are you going to work on it yourself? If so 2 strokes are easier than 4's. 4 strokes have constant power while 2 strokes don't.... The question should be more of how do you want to ride?

[@natebiegalle3962]

No measurements needed?

[@FirstGendodgegarage]

when he was torquing the bolts he didn’t pat them on the head and say “Well those aren’t going anywhere” I’m concerned they might go somewhere now

[@brandongleason4145]

🤘🏼🤘🏼💪🏻💪🏻👌

[@edbennett6236]

No cleaning of powervalves?😮

[@travelladdict5138]

Hello sir im Akash Im restoring my old two stroke bike I have few doubts ......... The mechanic told me its better to rebore the cylinder ........ ( The old piston is gone and it time to do second over size ) ...... Sir im doing my graduation and i dont have too much knowledge about the bike ...... Does boring and using a little tight piston make more power ? After reboring to next oversize Does polishing the piston and cylinder bore to a mirror finish make smooth run of bike and save it from geting seized .......... And Does polishing the piston and cylinder bore into a mirror finish make any perfomance I will wait for your reply

[@riversmith6382]

you still waiting? lol

[@DIXIEMAFIA251]

Are u still waiting?? Lol cause I am haha

[@peytonthomas4506]

how do i order the right size piston?

[@_kieranwilliams]

I’m sure on my 125 it’s stamped with a letter B, that’s my piston size

[@parkercarlson4210]

as i was putting the clips on my piston while watching this i dropped one in the bottom end… wish i had out paper towels down there

[@Marcelo-xw9nt]

i accidentally droped one of the clips in the crank shaft and I have no idea what to do. can anyone please help me

[@raccoon344]

Turn engine upside down and shake

[@snafuequals]

@@raccoon344 😂

[@robertococcia9815]

After all this work why dont you install boyesen or vforce3 reed valve. Bye bigfoot

[@kiddicool4616]

its so sad to see them go

[@classicbikerx3588]

Oiling your cylinder walls is dangerous. I glazed my first jug doing exactly that. Those rings would never seat.

[@anteriorblock9108]

I think I ruined my top end from not having enough oil in my gas and now my bike has no power, I think from a lot of metal on metal scraping

[@owendavies6097]

🤘

[@jameshawkins3484]

2 strokes rule.

[@dolotre]

Should’ve put a wiseco piston in it

[@owendavies6097]

First

[@svenixpa-swe6627]

Yes Owen was first

[@punisher8319]

SvEnIxPa-SwE then it must have lagged because it said 2mins and and Owens said 45 seconds

[@svenixpa-swe6627]

Ok

[@taavip9312]

2:19 on my yz 125 the thing just doesn’t come out of the piston!

[@groomlake51]

Because you can feel .002-.004 of a inch🤣

[@Norcaljedi_ea]

You lost me when you used a hammer on a wrench…😂 better check your Kitten mittens boy.

[@__mayo1802]

🤦‍♂️ i bet u have tons of friends

[@TheTraxracing]

Was I the only one who noticed the outer o-ring wasn't seated in the grove on the cylinder when he put the head on? 😂🙈

[@peytonthomas4506]

😳 hell notice when it starts leaking coolant

[@aarono.8925]

I should’ve listened... I dropped the circlip down into the engine🤦🏼‍♂️.

[@svenixpa-swe6627]

Dude get some gloves

[@TheMxFactory]

Whaaaaaaaat! People do this with gloves?!

[@jannep6772]

I can´t do this kind of work with gloves. Gloves are ”work brakes” =)

[@svenixpa-swe6627]

The Mx Factory Janne P ah ok I didn’t know

[@svenixpa-swe6627]

I meant latex gloves

[@robhayter484]

You failed to mention ring gap ??

[@trevornewton9687]

Does anyone actually rebuild there engine every 24 hours

[@evansydlosky5375]

Depends what riding you’re doing

[@badsanta518]

There is some misinformation here. You left a few steps out, too.

[@jdm4569]

Ive seen a lot wrong in this video. You need to at least check the ring end gap and mic the bore if you can, I never put new rings in without giving the cylinder a light hone with a 3 armed hone (thatll do 2 things, put some cross hatching in so the new rings will seat and tell you if your cylinder is perfectly round by looking for low spots) and lastly always install your piston circlips with the gap at 6 or 12 o’clock so the clip doesn’t compress when the piston is going up and down and come flying out and do a lot of damage…. bad instructional video imo

[@VibN117]

If you are coming here to rebuild your top end. Just keep on moving bc this isn’t it

[@VibN117]

The fact u skip 2 steps within rebuilding the top end just to save yourself time really shows your works quality & ability to last. Just some bullshit man. This is why people’s top ends last 5 rides after paying for rebuilds now days. Sick of seeing these lazy ass rebuilds. U r in there and want to skip steps that u could get paid for yourself for doing the extra work needed to complete a full top end rebuild. New bike low miles a lot of miles doesn’t matter. Just lazy.