YZ125 Bottom End build

Installing a new crankshaft in a dirt bike is awesome! Welcome to our YZ144 Build playlist! Today we rebuild the bottom end of a 2002 YZ125
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[@davidwagner1916]

You dont need a press to seat the crank into the cases. if you heat up the inner main bearings with a small torch or wind proof lighter the crank will slide in by hand. and it doesnt take much heat to do it.

[@highlandcycles]

Right on

[@tomatoknuckles]

Brilliant video. I was trying to put the transmission back into my 426 and gave up until another day, such a pain in the A.

[@highlandcycles]

Hahaha. It can be.

[@jodyhutcheson9891]

I prefer to use a crank puller, and a case splitter/puller for installing cranks and pulling cases apart or putting them back together.

[@highlandcycles]

That works great too.

[@michaelalexander1161]

Nice work mate!!!!

[@highlandcycles]

Thanks

[@theallegedmoonman3631]

Thank you

[@djcampbell9150]

You have to tap the crank with a mallet after installing. It will square it in the crank bearings / bore and rotate smoothly.

[@highlandcycles]

Good tip

[@codyjoseph44]

Do you center the crank? I had a yz250 crank that would get stiff to spin after trying case bolts. Turned out the crank was just a little too far right of center. It may have corrected itself during break in though.

[@highlandcycles]

I don’t worry too much about it on these bikes. There are some that you have to center but the yamaha’s will break in and be perfect as long as you are easy on break in.

[@jameselder56]

We are rebuilding a 02 yz 125 this has been so helpful thanks ! Do we need to mess with the case to bore it out?

[@highlandcycles]

Depends on the kit but the Athena one doesn’t require messing with the case

[@randomguy1807]

Is it necessary to replace the transmission bearings if need to you replace the crank bearings?

[@highlandcycles]

Not necessarily. It really depends on their condition and how many hours they have on them.

[@sturphy3036]

I pressed my cases together and the crank is a bit tight to move I made sure main bearings were pressed in pretty straight

[@highlandcycles]

If it’s not too tight it will loosen up when it warms up

[@theallegedmoonman3631]

Mf the supa villain

[@painsrides3616]

Its so interesting to watch engines go together.... Weird, right? 👀 The GPX is finally back in action 💪 seems the reg ec got smoked with all shorting form the loose connection. Its been down for over 6 weeks now with all this crap, but tomorrow... I Ride!!

[@highlandcycles]

Awesome man

[@chaka2178]

​@@highlandcycles q

[@chaka2178]

😊

[@jasonpattison8405]

Got a question for u I got an 2000 YZ 125 is there a ball bearing for the Push rod ????

[@highlandcycles]

Not sure. Have to look at a parts fiche

[@randomguy1807]

Were you hitting the bearings in on the inner race of the bearing? Is that bad to do?

[@highlandcycles]

No, I was hitting the outer race. Hitting the inner race is bad

[@mathew4203]

I have a 01 yz125 and keeps missing 2nd had it apart 2 times first it was not hitting neutral tore it down got new clutch’s got neutral back now missing 2nd straight to neutral any idea what could be wrong any ideas @ me

[@highlandcycles]

Not sure. Is a shift fork bent?

[@lost4058]

Just wondering what the cost of a complete rebuild of the motor like that would be. I have a blown yz 144, haven’t dug in to find exactly what happened but I’m just curious how much it might cost if all the internals needed replaced? Thanks in advance!

[@lost4058]

And please add in labor cost as well!

[@highlandcycles]

@@lost4058 usually it ends up being around $1500

[@carloscruz1112]

Is that something your willing to do? I have a 04 yz125 and the engine needs to be rebuilt

[@valeleroi9151]

I have a 2002 yz125 that I want to bore out to a 144. In the description of this video you reference a YZ144 Build playlist. I looked and didn't actually find this playlist. Please tell me I just don't know how to work KZbin . Where is it? I rode this bike for years and years and it's so clapped out. I'm too emotionally invested in it and want to go through the whole thing with freshies as a fun/aggravating/educational winter project.

[@highlandcycles]

I might have deleted that list but the vids are still up. But the main thing is that I bought the Athena 144 kit. It comes with everything you need.

[@TheBeedeegee]

What would all those parts run ball park estimate?

[@highlandcycles]

Full motor kit from wrench rabbit is about $600

[@thebullbog]

What are the dimensions for the 2×4 box

[@highlandcycles]

I don’t know and I’m not at the shop but it’s about 8”x14”

[@theallegedmoonman3631]

Hey is this the same bottom end as a 1994-95 yz im about to do my first full rebuild and I dont wanna waste my money also if you think I can do something to improve the design let me know please I love my yz

[@highlandcycles]

It’s close

[@theallegedmoonman3631]

@@highlandcycles cool thank you

[@laautiquiroz3086]

I bought a bike with this 144cc kit, and i have a question, the connecting rod used, is the original of 125? My bike is 2004, thank you

[@highlandcycles]

Yes it is.

[@laautiquiroz3086]

@@highlandcycles thanks for your answer. greetings from Argentina!

[@highlandcycles]

@@laautiquiroz3086 Salud!

[@loganc8195]

link yo shui

[@terrygreen4838]

Wondering if you answer questions?

[@highlandcycles]

Yep

[@terrygreen4838]

@@highlandcycles I did a rebuild on my 98 YZ 125. And got it all back together went riding. Everything is fine but I found the O-ring that goes between the cases. I failed to install. Where the water flows flows through the crank case. I did use Honda Bond. so I guess what I’m wondering is should I tear it back down and install that O-ring or just run it the way it is and hopefully it doesn’t leak antifreeze into the crank case. What are your thoughts? Thank you for any info.

[@davemac39]

Why wouldn’t you have a nice flat surface to rest the case halves on while you drive the bearings in ? That diamond plate bike stand work bench gave me anxiety

[@highlandcycles]

Lots of motor builders and mechanics use a 2x4 box like that. It provides cushion and allows you to get the cases oriented. Flat surfaces make it impossible to get the motor flat

[@JohnDoe-et4oq]

How much would a job like this cost ?

[@highlandcycles]

$900 if you bring the whole bike in

[@craigjarvis9677]

👍👍👍

[@highlandcycles]

Braap

[@richardhartley7094]

👍🇬🇧

[@highlandcycles]

@@richardhartley7094 Yeah

[@Lowkey_Lee]

What year bike is this you’re working on ?

[@highlandcycles]

This is a 2002