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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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

[@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!

[@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!

[@MRVW-32]

Just came from there 100 percent with you on that lol

[@damonjones9270]

Who

[@quavyguy9792]

same

[@robertgonzalez8419]

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

[@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

[@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 🤙🏾🤙🏾

[@grantyentis5507]

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

[@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🤷🏻‍♂️

[@TheWillGamerChannel]

Loving the series, keep em coming!

[@adampaganelli4891]

Thanks dude!

[@TwoThreadsAhead]

The Cerakote on your case and pump looks amazing dude

[@jt8251]

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

[@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 💪

[@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! 😇🙂

[@joneserupinsmoke9161]

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

[@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 - 🧐🙃🤪

[@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

[@slingshot3461]

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

[@johnguilbert1349]

Brappin'A Looks bad ass!

[@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.

[@AaronGoneWild]

Hey thank you i live with my mom ride a yz250 im 14 and i blew it up 1 month ago watched this and i just finished rebuilding it thx you helped me out btw the new top end and piston makes it run minty

[@glenholmgren1218]

If you want more bottom end torque (at the expense of top end HP) out a reed valve block spacer in - increases the crankcase volume

[@AaronGoneWild]

Glen Holmgren yea that works to

[@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?

[@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.

[@mikeinsanediego]

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

[@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?

[@huntergraviso]

You're gonna gain a ton of subscribers you keep videos up like this

[@adampaganelli4891]

Thanks man I really appreciate that!

[@huntergraviso]

I'm going to tell all my friends to watch this channel you could Also get a ton of views for just cleaning bikes those vids are satisfying to alot of people

[@adampaganelli4891]

Really appreciate that man!

[@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?

[@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?

[@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!

[@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

[@JohnJ77777]

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

[@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?

[@Vazerin]

How did it go? I'm doing my fiest rebuild on a 2001 YZ250, why I'm here

[@souliog]

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

[@archie3746]

How clean is that engine

[@patrickzychowski9314]

Really great video.

[@eduardogarcia9434]

Why 2 gaskets? Loving ur videos

[@erichildreth7562]

Nice work!! You know your stuff that's for sure! If you have not already get the Motion Pro Torque wrench adaptor, I got one and I use it for all four cylinder studs so they are all evenly torqued down and they give you a simple math conversion to set the torque wrench. Trust me it is worth it! :)

[@johncirivello1320]

Please answer why the use of two gaskets 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

[@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.

[@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?

[@frabcisbaez3681]

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

[@NorthCust]

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

[@christopherjohnson9993]

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

[@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.

[@dirtriderz4116]

Sick build man!

[@jonnymacdfilm7468]

Good video man!

[@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 $$$$$

[@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.

[@maxapollo1]

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

[@ionGuy123456789]

How do you check for play in the connecting rod? Which axes should allow movement? Just rotational right?

[@adampaganelli4891]

Normally up and down play is what you should watch out for. Some side to side play is okay.

[@ionGuy123456789]

Adam Paganelli ok cool. I have a tiny side to side wiggle but vertical feels pretty ok. You inspired me to buy a 2 stroke! My compression test only shows 60psi which seems way too low for the condition of the piston and cylinder. Any other reason you could think of that would account for that? It starts and runs fine.

[@Groot_G]

Nice to watch.

[@julianlaustsen1991]

is that clutch cover ceracote?

[@Vazerin]

Going to rebuild my first ever dirtbike engine, a 01 yz250, seen the videos, seem easy to do but I fear of messing up hundreds of dollars of parts

[@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

[@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

[@typgamer]

Greate video, Im thinking about rebuilding my '99 dt 125s crank and crank bearings...

[@adampaganelli4891]

Thanks man! Good luck

[@johnnyappleseed888]

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

[@juliebulauan5013]

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

[@CobraPhobic]

I'm your 3.000th like :D ^^

[@mattnoland8751]

Accurate and helpful. Thanks

[@davemcmullan2795]

How do you torque the cylinder nut inside power valve housing??

[@adampaganelli4891]

Using a crows foot

[@UlisesGlez26]

Great video, the bike is going to be sweet.

[@adampaganelli4891]

Ulises appreciate that man!

[@darrenmcbeth4465]

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

[@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.

[@michaellodice4093]

That power valve shaft does not have a seal correct? That was a bearing correct? My 02 only has a bearing there.

[@adampaganelli4891]

On the 03 there is a seal like in this video. On the 2002 it is bearing

[@michaellodice4093]

Damn you are good! Wonder why they changed it. You’d think with the heat they wouldn’t have a seal in there. Anyway great video I enjoyed it. You do fantastic work it’s a pleasure to watch. Keep it up brother!

[@dalesmit7869]

Have you used a nickasil coating on the cylinder wall?

[@ruiesteves304]

How many time and temperature you heat the painted peaces ?

[@jgbelmont]

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

[@Furrylicorice]

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

[@user-fe3gz5sg5v]

How did you torque the studs down

[@cameronloeffel8099]

Where did you get that red top end cover or what paint did you use

[@adampaganelli4891]

It’s from phatheadracing

[@ajeje6933]

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

[@carternisely904]

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

[@mattnichols1693]

What's that coating you have on the engine and why dont you have it on the whole engine?

[@adampaganelli4891]

It’s called cerakote. And I wanted to have some polished aluminum on the engine

[@wyattjameson1860]

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

[@kelmendabazi6281]

how did you solve the problem of the traverse of the exhaust?

[@adampaganelli4891]

Not sure what you mean

[@mlakarx2931]

Love your videos keep up and make more videos please!

[@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

[@davidkirchner579]

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

[@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

[@kenyiz]

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

[@patricklions9066]

impressive

[@adampaganelli4891]

Thank you, I’m glad you enjoyed!

[@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

[@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.

[@danielsimpson8929]

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

[@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.

[@NRecob]

Got a part # for that Scotch Brite? Thx!

[@adampaganelli4891]

No, but just type in scotch brite on amazon

[@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!

[@johnnyappleseed888]

why do you have to have more compression in order to run race fuel?

[@adampaganelli4891]

It’s the other way around the more compression I have the more i need a higher octane fuel to reduce pre detonation.

[@2007deadeye1]

@@adampaganelli4891 I didn't think you had pre-ignition with a oil & gas mixture on a 2 srtoke?? Am I wrong

[@joseedgardojacquez377]

Its the same process with a honda 250r? 2000?

[@adampaganelli4891]

Cr?

[@billymcculloch-hardenduro2755]

Hey man what sort of liquid is running in that parts washer

[@adampaganelli4891]

It’s a Costco oil eater I’m thinking of switching to simple green

[@jaidonlusk885]

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

[@zemeche5493]

are my power valves opening up against what I ought to be?

[@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

[@zorp12345]

Is is fairly simple to rebuild engines? I’ve never worked on bike engines before and I have a ktm exc 125 2003 that needs a lot of attention! Thanks

[@adampaganelli4891]

If you a some special tools have the service manual you can make it happen!

[@zorp12345]

Thanks for the support bro! I think I have the confidence to do it :) I’ve got all the manuals so should be okay, what special tools is required? Thanks again!

[@kx7zz]

zorpRc did you ever do it? how did it go?

[@zorp12345]

@@kx7zz hi yes I rebuilt it about 4 months back, it was actually surprisingly easy, obviously the first time doing it was slow and confusing but with the manual it made sense, though if I was to do another rebuild I know exactly what to do and how to take it apart and put it back together

[@kx7zz]

zorpRc that’s great to hear! I’ve got a kx125 that needs the top end rebuilt. Aside from basic maintenance I’ve never worked on bikes before but i knew I’d have to wrench on the engine eventually. i think the top end shouldn’t be too hard though.

[@sharkiesgirl8929]

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

[@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.😂

[@jakeharling9971]

Why did you use two gaskets?

[@adampaganelli4891]

In the video I said it’s what the guy at phat racing recommends with his h14 cylinder head. It allows the squish tolerance of the cylinder to be at an optimal range where I can still have high compression but not sacrifice much on top.

[@noah8877]

I thought you were never supposed to hone a plated clyinders ?

[@adampaganelli4891]

Technically you are right. You don’t want to necessarily hone the plating, you just want to scuff it up so the rings can seat properly.