Everything You Need To Know About Rebuilding A Two Stroke Top End

In today's episode in the cr125 build series, I am going to be putting the top end onto the cr125 engine. I am going to be installing the piston and cylinder. I will show you guys how to measure your cylinder to piston clearance with a cylinder bore gauge, as well as how to measure your piston ring end gap using a feeler gauge. I will also show you how to disassemble and service your power valve system. After all of this, I will be putting on an aftermarket cylinder head made by Phatheadracing. If you guys are interested in any of the products I use check them out down below!
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Links to Products: (If you want to help support the channel so we can continue to create new content for you to enjoy, I encourage you to shop through these links.)
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Power Sports Builds is a channel focused on teaching people to restore and customize any sort of power sport equipment they have. We work on jet skis, dirt bikes, street bikes etc. We also look forward to bringing how to video courses covering the basics all the way up to advanced skills in topics like electrical, two stroke engine repair, four stroke engine repair, brakes, suspension, painting processes and fabrication. We appreciate you following us on this journey and don't forget to like and subscribe!
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[@adampaganelli4891]

Thanks for watching! If you are looking for a way to support the channel consider shopping for your Powersports parts at The D Zone. I also put together a list of my most commonly used tools for you guys to reference- thed.zone/product-tag/tool-collection/?count=36&orderby=popularity&ref=AP34

[@mikedouglas6538]

How many miles can one expect to get from. A 150cc 2-stroke that hasn't been dogged? I'm looking at Vespa with 8,000 miles with a 4-speed manual. Any clue?

[@njmotovlogs7132]

Same brooo

[@bonquiqui4612]

Do you need to just use a seal for the power valve mine has a bearing it’s the same bike year and everything

[@mr.channel6467]

What happens if your piston size is wrong

[@mr.channel6467]

U never mentioned why u used 2 gaskets there

[@mikegro8502]

Haha... when I first saw the thumbnail, I thought Cameron Niemela has uploaded a new video. xD

[@speedskid4838]

Mike Groß I swear this guy is copying Niemela. I swear.

[@ryanowens2653]

Me too!

[@CRAZYRUSTYVW]

Just came from there 100 percent with you on that lol

[@damonjones9270]

Who

[@quavyguy9792]

same

[@joneserupinsmoke9161]

That's a clean looking engine bro👍👍

[@lishchynsky27]

You said you were gonna explain why you put 2 cylinder gaskets on but you didn't

[@Dylans503]

He didn't measure the squish band or check timing either

[@matthewhallman3453]

@@Dylans503 2 strokes don't have a timing chain

[@Dylans503]

@@matthewhallman3453 a timing chain is for valve timing, that's not what I was talking about. ignition timing can be changed by the stator position to either retard or advance the spark. Look up 2 stroke timing.

[@glenholmgren1218]

Matthew Hallman ?... He means ( Port )Timing - Period ... NOT Timing Chain. OK - I see I should have read HIS response first ... obviously (now) I see they were talking about ignition timing, as opposed to Intake / Exhaust Timing - 🧐🙃🤪

[@eduardogarcia9434]

Why 2 gaskets? Loving ur videos

[@carternisely904]

you should start case matching it will give the motor a whole lot more power

[@mlakarx2931]

Love your videos keep up and make more videos please!

[@Vincentschneider007]

Adam, use my cr125 for shifter kart racing. Problem is the front mount hole has wallowed itself out larger than the 10mm bolt. And I believe the rear one has damaged itself also. Not sure how this happened as I check them, but it did. Any suggestions on repair or just get new cases, uggg $$$$$

[@dalesmit7869]

Have you used a nickasil coating on the cylinder wall?

[@NRecob]

Got a part # for that Scotch Brite? Thx!

[@adampaganelli4891]

No, but just type in scotch brite on amazon

[@alexfro8408]

What if you can’t find parts, I have a rotex 2 stroke from the 90s, and I can’t find any parts, can anybody tell me where, or a website that C could possibly find for

[@Jxrd99]

Did you figure it out? I'm looking into old 90s dirt bikes but I really am worried about finding rebuild kits, cylinder sleeves, etc.

[@petergazagnaire4747]

The fact that siri said "about" worries me

[@Bardy80]

And ima buy a four stroke

[@MrSuperrajab]

Inches.... why do you do this to me America why...

[@adampaganelli4891]

For real

[@dominiknowak4525]

Halo polska jesteście ?

[@user-ht8kw3jm7k]

You are a carbon copy of Cameron Niemela thubnail parts washer even cr125. Planing on building a 250 next lmao. At this point just plug HIS merch

[@thedaddiproject8638]

In case you don't entirely grasp your value... I'm here to inform you that this is easily some of the most comprehensively-valuable engine tutorial on this entire platform! Beautiful presentation. Beautiful instruction. Just all around & perfectly BEAUTIFUL! There was a time when it would take years of boring classes to learn what you've taught in mere minutes. It's people like you who have taken teaching to a whole new level. Thank you for bringing so much value to KZbin.

[@michaelmccabe2404]

Agreed. Brilliant - Thanks Adam!

[@Twowheeleddevil]

I just want to give everyone a couple tips on not just 2 stroke engine’s but pretty much anything in general. When you’re taking something apart that you’re not experienced with or you don’t fully understand take pictures and take notes. “For (Such and such) part, the washer goes on then the 10mm bolt” take photo’s of each bolt and the part before you take them off so you can look at those later and figure out how to put it back together. While you’re doing all that look at the different parts, look at how they work and learn about stuff. My Father completely took apart a V8 and was able to put it back together a year later because he found the old photos and notes

[@ionGuy123456789]

I think you have inspired me to build a two stroke. My wallet hates you! Lol

[@adampaganelli4891]

You’ll forgive me when you take your first ride

[@glenholmgren1218]

Your wallet should LOVE him - nothing has more Free Lunch, sweat equity upgrades than a factory detuned 2-Stroke! 😇🙂

[@FULLTHROTTLEFILMZ]

Excellent information! Wish I knew some of these things when I did the CR250 top end! But hey, motor hasnt blown up yet haha. Great vid man.

[@adampaganelli4891]

Your good man we’ve all slapped it together and ripped before🤷🏻‍♂️

[@robertgonzalez8419]

It’s guys like you that make KZbin what it was intended for awesome info God bless

[@HenryDarr]

Can't wait to see bottom end rebuild and in depth transmission tutorial 🤙🏾🤙🏾

[@adampaganelli4891]

I already have one on the page!

[@HenryDarr]

@@adampaganelli4891 Sweet as 🤙🏾🤙🏾

[@DPJAB]

You lost me at 5000 of an inch!

[@owenreed4432]

Same

[@yanicemtl]

@@owenreed4432 why don't y'all just use the metric system smh

[@maxapollo1]

Oki watched the whole vid ..where do i send my engine ;)

[@travis4308]

Lol you should work at a shop assuming you don’t already. Everyone made this super easy and they work and it’s fun then you come in make it to complex and take all the fun out of it and make everyone buy a million math tools and sitting there all judgy and stuff. 🤣🤣🤣

[@landlord8492]

Travis T 😂😂 facts

[@travis4308]

TARIK HILL I’m over here thinking I need a few wrecks and stuff and he is over here talking about getting a spectrometer

[@father_dev]

What are the torque specs for the cylinder bolts and also the cylinder head bolts? I know the nuts go to 20ft/lb but what about the new bolts?

[@woodymx3488]

04 - 07 CR125 manual shows 9 ft lbs for the cylinder head studs (equivalent to 108 in lbs), since they're the same thread I would think the same torque for cylinder studs as well?

[@jordyjordan9151]

Hey man love your vids. I work on practice bikes for Mitchell Harrison if you're into racing at all. I'm a machinist as well and I just caught the bit on metrology and piston clearance. You can still get totally accurate readings down to .0005" if you just lift your caliper to clear topside. Essentially set the piston on it's head and stand skirts up then come in from the top at like 45° with the caliper. Or as you said you can go with a mic. But don't take this as a dicky comment bro from one mech to another I know how sometimes those little tips are important! That's why your vids are doing well too man you do a fantastic job of showing the right way while explaining WHY it's right. Cheers from Temecula CA brother! Keep em coming.

[@jordyjordan9151]

Also setting the bore gauge is definitely better to use a mic and gauge blocks. And converting to or from metric always multiply or divide by 25.4. Just machinist talk but you are completely capable of doing all that man. The math you're doing is well beyond the measurement technique. In other words you have too many opportunities for human error, you are doing math down to ten thousandth placement. To put that in perspective to other people, one human hair is .003 and you're using decimals down to +/-.0005 so thats 1/6 dia. Of a human hair lol so if you use that tight of numbers on math you really can't trust setting bore gauge off calliper and then doing that math to get difference. Instead. Use a 2" and a .130" gauge block and set a 2-3" micrometer then use the dial on bore gauge to set ZERO at exactly 2.130 then you let the gauge work for you just read the dial and you will have the best reading I think you get the idea. You're killing it man hope these couple tips only further your success

[@adampaganelli4891]

Thanks for the ideas! I’m always willing to learn from someone

[@adampaganelli4891]

Especially when done in a constructive way

[@jordyjordan9151]

You ain't gotta tell me I can see clearly you like learning. Doing all your own stuff and doing it well. Then filming editing and not to mention understanding how to produce a vid like yours. You're killing it man 💪

[@Cletus1927]

I’ve bought a 79’ Yamaha yz125 in pretty good condition but I want to take apart the top end before I start trying to run and ride it, does anyone have any tips?

[@sharkiesgirl8929]

I used purple cleaner to clean out carbon inside 4 stroke ate the finish nickle plating right off it. So mad.. never again

[@brandonbeaubien9386]

So do you have to do this every single time you replace a top end.

[@northtexasskies3243]

Pretty much

[@chadcoady9025]

It doesn't take long though and completely worth it. Trust me, it's better to do it right than to take the easy road and have a piston skirt break off and punch through the bottom of the case. Don't ask me how I know (twice). I have a broken Blaster 200 case and a broken RM125 case from years ago.

[@timothyhackett7372]

my old engineering lecturer used to call 'Vernier's' "Very nears" because there not very accurate for high precision applications like engine building. you should be using a micrometer for that piston diameter

[@jt8251]

I'd also recommend using the bore gauge to first check concentricity (roundness).

[@knaaxi]

ive ran into a problem where i got a new cylinder for a cr250 and i reused the old studs but they were very hard to get in and one didnt go in all the way and i ended up destroying the thread on the stud. I was curius if i should always change the studs too when i install a new cylinder I have also heard that the studs are only made for one time use, as if you would need to replace them everytime you take the head off.

[@archie3746]

How clean is that engine

[@tipsysmichigander6483]

A well made non biased video just telling you how to do the job. That new cylinder head looks pretty shotty. Sloppy job nice color.

[@johndyett431]

If you running you bike that rich Charing to castrol power 1 I have no problems

[@grantyentis5507]

This was a fantastic, extremely well done video! Thank you for taking the time and making it available!

[@lordfashion9892]

love your stuff bro. i watched you back in the day and then i got out of motocross but i just bought 2 bikes so im back in and watching all your vids. sub from me bro!

[@450ktm520]

My friend did one ride and found out the hard way. Your video has you 0.010 larger on the size, and like you said you might be +/- the reading. My friend was + 0.030 and scratched up his cylinder.

[@adampaganelli4891]

Piston size is within spec?

[@450ktm520]

@@adampaganelli4891 around the 7 Minute mark, during that whole thing. You calculated .07 mm, what I didn't understand, if we were out of range but at the same time still within range. Can you help explain how it's still in spec

[@danielsimpson8929]

You didn't explain the double oem cylinder head gasket...

[@JohnnyRebKy]

Why do they need a rebuild so often?? Or is it just the high revving dirt bike engines? I have a Polaris 400 2 stroke and they go for years without a rebuild. But it also isn’t near as high revving and it’s water cooled too. I guess I could see why a high rpm 250 would need a rebuild more often than the big 400 2 stroke

[@nikolaystoykov9413]

So why the two gaskets on the cylinder? You didn't explain in the end.

[@lishchynsky27]

I am curious as well. Less compression with more gaskets, might have something to do with the different head

[@johncirivello1320]

Please answer why the use of two gaskets gaskets ??????

[@elijahplays28]

litteraly an exact copy of cameron niemela but good vid

[@NTRGFX]

Great videos man, What brand of piston are you using? It looks like a vertex to me with coated skirt but just wondering. Keep the videos coming they are excellent.

[@UlisesGlez26]

It is a Vertex piston, he used a wrench rabbit kit.

[@bigironjakesd619]

I need more info on the power valve. I ha e a 02 cr125 just opened the power valve co er and everything is totally lack caked on oil. What does this say about the bike and can I just clean it with a spray?

[@TheMcMeow]

Awesome video! Looking at buying my first dirtbike soon. Seems pretty straightforward maintaining a 2 stroke. My mechanic friend always tells me to stay away from them cause he claims they break a lot more often and are harder to maintain. I'd say otherwise though, when a 4 stroke breaks it's a lot more expensive and harder to repair. Am I right?

[@johnnyappleseed888]

ive heard that you should only deglaze if your running castor oil

[@socks2441]

do the cylinder head studs come in a pack? i wasnt really planning on replacing them, even though they are a bit rusty. but if there is an engine rebuild pack that has them i would do it.

[@deejdvs]

Great video. What I did not see was drilling the two holes in the piston for the exhaust bridge. Also, do you need any type of grease or oil on the shaft for the exhaust valves?

[@jenniferbradshaw298]

hi like your videos,they are helpful to me,i have a 94 cr125,what kind of gear oil is the best to use and what coolant should i use.i,and how do you know if the radiator pump is still working/if you could help me i would appreciate it,thank you.

[@stephaneracicot791]

hello adam good job there...i got a 1982 cr 125r coud that engine fit possibly inmy 1982 frame tanks again good job my friend

[@hitaanharrastelijakuskinma8640]

Most calipers are not accurate enough to measure piston or cylinder. Accuracy can be 0.1 - 0.05 mm. I wouldn't use mine to check for clearances.

[@christopherjohnson9993]

Why did you use 2 base gaskets let me know pls thanks

[@nathanmescher6840]

Hey i have a 2000 cr125 and I’ve been watching everything in your videos and i noticed that on my bike and rocky Mountain’s diagram that the little spacer for the lifting rod for the power valve you put it on backwards compared to mine. Im not saying its a big deal or even wrong i just caught it.

[@adampaganelli4891]

Thanks for the input I will take a look tonight

[@nathanmescher6840]

Power Sports Builds Rockymountian has it on exhaust valve schematic

[@stuarthipkins8336]

You never explained why 2 base gaskets

[@gusssfraba]

ciao Adam! beautifoul rebuilt. may I ask you what kind of color (I mean the cerakote name of the color) did you use for the covers, specially the grey one. thanks

[@jewkvlogs7495]

Your doing waaayyyy to much. Had to stop watching. Sorry

[@CobraPhobic]

I'm your 3.000th like :D ^^

[@0nionbooty]

why did you used 2 oem gaskets? couldnt find the explanation later in the video

[@darrenmcbeth4465]

I have a question. I have a 2001 CR250R 72.00mm what size of piston do I need??

[@TheWillGamerChannel]

Loving the series, keep em coming!

[@adampaganelli4891]

Thanks dude!

[@NorthCust]

great video, just what I needed. thank you :)

[@souliog]

I keep a can of Seafoam or B12 around for clean-up. Carbon melts off in seconds.

[@TwoThreadsAhead]

The Cerakote on your case and pump looks amazing dude

[@PokeyCottons]

The more I learn how to do this, the more it makes me just want to replace shit at recommended service intervals.

[@vitsin87]

This is too mathematical for me, just put it in and make sure it's not to big or small, job done, hahaha

[@JohnJ77777]

Is a vertex a cast piston? Why didn't you drill 2 holes in the exhaust port side?

[@davidkirchner579]

Hey not trying to tell you what todo but Scotch-Brite has aluminum particles in it

[@willrichards6976]

I’m 14 and bent the frame of my beta cross trainer. Wish me luck🤕

[@jake-zi4px]

Im 15 and my 86 yz490 just threw a rod a couple of hours ago, and now I got a goddamn crater in the bottom of the engine. Wish me luck too

[@willrichards6976]

jake76 yeah good luck with that😂 my bike needs new plastic, new frame new forks and new piston. Lesson learned don’t go the wrong way on a track.😂

[@MrTurtletraxx]

Adam, where is the source for the stud insertion tool?

[@adampaganelli4891]

Studs were inserting using two nits tightened against each other. No tool was necessary besides a torque wrench

[@robertbenson6147]

The mount bolt hole is on the wrong side Otherwise a nice video

[@robertbenson6147]

The head mount for the frame

[@jaidonlusk885]

Good video but why did you waite untill your hands where already dirty to put on the gloves

[@father_dev]

Rebuilding my CR currently...debating if I want to take the time to clean it up or not. Can I ask the process you used to get that cylinder looking the way it does? Also, the painted covers - is that powder coated or did you paint it yourself?

[@adampaganelli4891]

The covers are done using cerakote which can be found @ www.cerakote.com The cylinder was done using Mother’s aluminum polish.

[@jgbelmont]

What if you have very thick grease and water all over your crank and rod?

[@Red5Won]

Another fantastic video! Thanks so much man. Do you think you can do a full cylinder prep video sometime?

[@adampaganelli4891]

Yes, definitely coming in the future!

[@adrianlozano2687]

Why you put 2 gaskets on the cylinder?

[@jesse469]

To get correct deck height

[@robertbenson6147]

Hey you put the head on reversed

[@juliebulauan5013]

hi bro do you have any extra complete cylinder head for cr125

[@Furrylicorice]

Great video. Now I need to get to work on my bike. After I buy more tools 😁

[@Craig_450]

I’m gonna attempt a rebuild for the first time next winter. Not gonna lie, im a little intimidated for my first time😅 hope I can get it done and don’t end up regretting it. I wanna learn

[@xgdubjrx821]

How did it go?

[@SarasotaBayOMC]

Not every 2 stroke like this lol

[@frabcisbaez3681]

I don't know how you know so about engine but thanks for all those datail thanks

[@graydonparry1146]

That’s not how to use a bore gage

[@julianlaustsen1991]

is that clutch cover ceracote?

[@mikeinsanediego]

Where did you get that black side cover...it looks great

[@ajeje6933]

Hello can you tell me how NM prigionieri of the head please?

[@joneserupinsmoke9161]

That's a clean looking engine bro good job my man

[@kenyiz]

Can you make a video in Rotary Rebuild ... For Go Kart Engine ...

[@wyattjameson1860]

How much would it cost to buy a new top end for a crf150r?

[@frabcisbaez3681]

And I also subscribe to your Chanel plus and 👍

[@azide_rdx7937]

why tf you look likte that

[@muriloserpa3392]

Top

[@shokrefumi]

that's a really complicated way to use a bore gauge! make your life simple by buying a micrometer, instead of using the aproximator!

[@adampaganelli4891]

I agree, I need a quality micrometer.

[@MS-ih9ws]

Jesus loves you 🎉❤😊

[@onenessseeker5683]

Like to do things the hard way mate don't ya lol

[@timbyford21083]

A co-worker of mine just gave me his 02' 250r race bike. Stock engine with race forks and shocks. Going to be getting alot of views from me... Obviously. Will be posting videos as soon as I can.

[@adampaganelli4891]

Awesome man! Welcome to the channel

[@slingshot3461]

Youre a god at your job so clean and esy to understand

[@joneserupinsmoke9161]

That's a clean looking engine bro👍👍

[@DOCUPESCATV]

like bro