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YZ125 2002 yz125 bottom end rebuild

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Hello all 

I just bought a 2002 YZ125, rode it this weekend and it runs great no weird noises and great power, plug is nice and chocolate. was a little hard to downshift sometimes but over all ran good.  I drained the oil after my ride and found aluminum powder and small shavings in the oil  all aluminum non iorn . i plan to inspect the top end and take the side cutch cover off to inspect everything, i have no problem doing a top end and clutch work but feel uneasy splitting the cases. i dont race so i just want it reliable and would hate to keep riding it and do further damage. I live in the San Francisco bay area and wanted to know if anyone has a recommendation on where i can take my  engine to a reputable person who will do a bottom end rebuild if needed. Just want s good professional reputable place. any recommendations would be appreciated.

Thanks    

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Do you have some reason to believe it might need a lower end, or just covering your bases?

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2 hours ago, Doug Christian said:

Don't be intimidated to split the cases and do the bottom end yourself. It's very simple. If I can do it anyone can lol.

I’m Intimidated 

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Just rebuilt my 02 bottom end in this thread.

 

it’s not that hard, get yourself a case splitter, a crank puller, and some yamabond 4 with a small paint brush. The hardest part is the damn shift forks and the shift drum. They’re little bitches.

 

in that pic is what my “stuff” looked like. It’ll get in your transmission bearings and starts eating them up. Clean it up if you want it to last. My shift drum bearing felt a little gritty. Blasted it with brake cleaner and moved on. If you want to replace it, get yourself a “NSK 6905DDU” bearing and pluck out one seal with a razor. Done. Or go OEM, whatever bakes your biscuit.

8AA5A635-CA61-4EED-8545-E16A16E261E9.jpeg

Edited by Sullysully

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I’d also like to add putting the shift linkage together kinda sucks. There’s little tiny pieces in there you can’t lose, so don’t lose them.

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1 hour ago, Sullysully said:

I’d also like to add putting the shift linkage together kinda sucks. There’s little tiny pieces in there you can’t lose, so don’t lose them.

yes they absolutely suck.  i hate that shift pall assembly or whatever its called.  those stupid little dog ears are so reluctant to stay in when re-assembling that.  also i hate how you have to hold that plate over the shift pal assembly in order to get it back together.  legit took me half and hour to get that back together

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1 hour ago, mr.blaze said:

yes they absolutely suck.  i hate that shift pall assembly or whatever its called.  those stupid little dog ears are so reluctant to stay in when re-assembling that.  also i hate how you have to hold that plate over the shift pal assembly in order to get it back together.  legit took me half and hour to get that back together

Yamaha engineer: “I know how to piss them off. Check this out.”

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Simple to do yourself with the right tools. Tools are probably same price to ship 2 ways to AZ.

There are plenty people here to walk you through it and the trans is much easier than a 250. 

Didn’t see thread till now, took the day off yesterday for a trip to Grand Canyon with grand kiddos.

Was a beautiful day. 

534AC554-8D7F-46BF-8C68-008FE0C39262.jpeg.8b3d25477466ece4f8c77f8334588828.jpeg

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When I did my 06 125 last fall I swear the hardest thing was getting that stupid little seal out on the clutch actuation arm in the left case half.  I thought I was going to mar the seating surface for sure!

I have split cases on quite a few street and dirt bikes over the years and never ran into any major issues, but you DO need the right tools.  Don't be that guy that tries to get by without a proper splitter tool or uses other short cuts.

I am of a mind that if you are going to go to all the trouble of splitting the cases on a bike that old, you might has well replace ALL the bearings.  A transmission bearing kit, as I recall, was only about $80.  

In the past I have used OEM parts, or bought parts (like seals and bearings)  piecemeal as needed from a local industrial supplier.  For my YZ however, I decided to go with the Hot Rods kit, and I have to say I was impressed with the packaging and completeness.  I will continue to use kits in the future. As for the specifics of the HR kit, the only thing it did not contain was the woodruff key for the crank, so don't lose the stocker.  

I've never been much of a video watcher (I'm a shop manual guy), but the last time I did, and I have to say I picked up some good tips.  Two that I remember:

1. Use a couple of zip ties to hold the gear clusters and shafts together, and remove it as one unit.  That really allows you to see how things go together, and where the forks go, etc.  I wish I had thought of this before--especially that time my son (who was about 5 at the time), decided to play with the Suzuki RM gear clusters left on the work bench.

2. In another video, a guy heated up an impact socket with a shop torch, and set it on the inner race of the crack bearing (already installed in the case).  After a minute or so of heat transfer, the crank dropped right in, no crank puller needed.  Damn if it didn't work just like in the video!  But you will still probably need the puller for the other side.

Bottom line--if you think motorcycles are going to be a long term hobby and you have some space to work, go ahead and get the tools and learn to do it.  If you think dirt bikes might be a passing fancy, go ahead and just pay a good shop to do it.  

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18 hours ago, YZDOC said:

Simple to do yourself with the right tools. Tools are probably same price to ship 2 ways to AZ.

There are plenty people here to walk you through it and the trans is much easier than a 250. 

Didn’t see thread till now, took the day off yesterday for a trip to Grand Canyon with grand kiddos.

Was a beautiful day. 

534AC554-8D7F-46BF-8C68-008FE0C39262.jpeg.8b3d25477466ece4f8c77f8334588828.jpeg

Nice pic!  I've got some family out in AZ, and I'm looking forward to getting out that way for another canyon visit once this Covid stuff is over.  If you're an east coast guy like me, the size and spectacle of the stuff out west boggles the mind!

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4 minutes ago, rpt50 said:

When I did my 06 125 last fall I swear the hardest thing was getting that stupid little seal out on the clutch actuation arm in the left case half.  I thought I was going to mar the seating surface for sure!

I have split cases on quite a few street and dirt bikes over the years and never ran into any major issues, but you DO need the right tools.  Don't be that guy that tries to get by without a proper splitter tool or uses other short cuts.

I am of a mind that if you are going to go to all the trouble of splitting the cases on a bike that old, you might has well replace ALL the bearings.  A transmission bearing kit, as I recall, was only about $80.  

In the past I have used OEM parts, or bought parts (like seals and bearings)  piecemeal as needed from a local industrial supplier.  For my YZ however, I decided to go with the Hot Rods kit, and I have to say I was impressed with the packaging and completeness.  I will continue to use kits in the future. As for the specifics of the HR kit, the only thing it did not contain was the woodruff key for the crank, so don't lose the stocker.  

I've never been much of a video watcher (I'm a shop manual guy), but the last time I did, and I have to say I picked up some good tips.  Two that I remember:

1. Use a couple of zip ties to hold the gear clusters and shafts together, and remove it as one unit.  That really allows you to see how things go together, and where the forks go, etc.  I wish I had thought of this before--especially that time my son (who was about 5 at the time), decided to play with the Suzuki RM gear clusters left on the work bench.

2. In another video, a guy heated up an impact socket with a shop torch, and set it on the inner race of the crack bearing (already installed in the case).  After a minute or so of heat transfer, the crank dropped right in, no crank puller needed.  Damn if it didn't work just like in the video!  But you will still probably need the puller for the other side.

Bottom line--if you think motorcycles are going to be a long term hobby and you have some space to work, go ahead and get the tools and learn to do it.  If you think dirt bikes might be a passing fancy, go ahead and just pay a good shop to do it.  

I personally passed on that hot rods kit. They source their bearings from Taiwan. I’d rather go Japanese.

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6 hours ago, rpt50 said:

Nice pic!  I've got some family out in AZ, and I'm looking forward to getting out that way for another canyon visit once this Covid stuff is over.  If you're an east coast guy like me, the size and spectacle of the stuff out west boggles the mind!

Standing on the rim and looking down, focusing on how deep that hole really is, is pretty damn mesmerizing. You look back up to talk and it’s almost as if you just got off a merry-go-round, the ones at local parks that you can spin as fast as possible, not the damn up and down horse ride.

I think HR kits are a little skimpy on the manufactured bearings  unless they are Koyo, or better, pass on them  otherwise you are Replacing good bearings (no matter the age) for cheaper ones. ProX, KOYO, NTN, good stuff. I’ve found that HR are branded for themselves, and that is sourced from the cheapest no doubt. 

9AE58CCD-5A21-48B6-907B-D1829087A767.thumb.jpeg.f145169a9195810df3aeb8d6b8764f2e.jpeg

The two grommets and Opa  first time they looked into it. Just love this place. I remember it used to be part of a yearly pass, it is now $35.00 for seven consecutive days, no annual available. Couldn’t believe the amount of people taking family photos with masks on. Not crowded at all, that just blew our mind. 

 

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The governor just made masks mandatory in public for my state.

 

Koyo, SKF, NTN, NSK, and Timken are good bearings in my book. Anything else doesn’t have my trust.

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15 hours ago, rpt50 said:

When I did my 06 125 last fall I swear the hardest thing was getting that stupid little seal out on the clutch actuation arm in the left case half.  I thought I was going to mar the seating surface for sure!

I have split cases on quite a few street and dirt bikes over the years and never ran into any major issues, but you DO need the right tools.  Don't be that guy that tries to get by without a proper splitter tool or uses other short cuts.

I am of a mind that if you are going to go to all the trouble of splitting the cases on a bike that old, you might has well replace ALL the bearings.  A transmission bearing kit, as I recall, was only about $80.  

In the past I have used OEM parts, or bought parts (like seals and bearings)  piecemeal as needed from a local industrial supplier.  For my YZ however, I decided to go with the Hot Rods kit, and I have to say I was impressed with the packaging and completeness.  I will continue to use kits in the future. As for the specifics of the HR kit, the only thing it did not contain was the woodruff key for the crank, so don't lose the stocker.  

I've never been much of a video watcher (I'm a shop manual guy), but the last time I did, and I have to say I picked up some good tips.  Two that I remember:

1. Use a couple of zip ties to hold the gear clusters and shafts together, and remove it as one unit.  That really allows you to see how things go together, and where the forks go, etc.  I wish I had thought of this before--especially that time my son (who was about 5 at the time), decided to play with the Suzuki RM gear clusters left on the work bench.

2. In another video, a guy heated up an impact socket with a shop torch, and set it on the inner race of the crack bearing (already installed in the case).  After a minute or so of heat transfer, the crank dropped right in, no crank puller needed.  Damn if it didn't work just like in the video!  But you will still probably need the puller for the other side.

Bottom line--if you think motorcycles are going to be a long term hobby and you have some space to work, go ahead and get the tools and learn to do it.  If you think dirt bikes might be a passing fancy, go ahead and just pay a good shop to do it.  

 

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Thank you! Might just order the tools and give it a go. Looks pretty straight forward. Just not sure what in need to look for on the intermittent hard shifting. Anything I should be aware of ?

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