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06 yz 125 complete engine tare down

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I recently picked up an 06 YZ 125 and have decided to tare the whole engine apart after finding that the shift stopper bearings were missing. I also found some steal shavings in the oil. So far I got the clutch out and found a wear mark behind the basket on the case, anything I need to do about this? (pic below). Luckily the bike shifted smoothly into all gears and ran fine, first gear and neutral took alot of pressure to engage though. I know I will need a case splittler, clutch holding tool, and flywheel puller for the bottom end, is there anything else I will need? Pic below of the yz I'm working on, I'll keep the thread updated with pics as I tare into the motor. 

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Edited by crmaverick

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That's a nice bike, looks like a low hour example. As far as the engine, I'd definitely split the cases, put a piston, crank bearings and seals in it, and get those floating bombs out of there...

Keep us updated!

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No that wear mark is not in a real important area long as it isn't super deep and caused any cracks in the case, just smooth it up when you have it apart looks okay to me what from I can see in the pic.

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Thanks for the replies. Does anyone know what tools I need to rebuild a bottom end? trying to get everything at once

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you definitely want special/right tools.

Bearing press

Crank/case halves installer

Case splitter

Tool to remove clutch assy.

Leak down tester

Torque wrench

Dial indicator for timing.

That's off the top of my head

Edited by Mrbinkels

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Should I get the complete gasket kit or just the top end kit + yamabond for the cases? Should I also be replacing transmission bearings and is there a way to check if they need to be? 

 

Thanks 

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Why not replace all the bearings and seals you will need a blind bearing puller tool that goes down to at least 8mm inner diameter.

Check bearings for smoothness by hand they should spin freely with not catching or binding in them.

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Ordered up all the tools I need to split the cases. Do you typically need to replace shifter forks and transmission gears? I'll post pics up when I get it apart but was wondering how to tell when gears and shifter forks need to be replaced (other than the obvious when a gear is chipped). Anything else I should do while its apart?

 

Thanks 

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I needed to buy a flywheel puller, rest of the tools I made do or built myself. You have a good list going there

 

Here, DL this, its the manual for that bike (free legit pdf service manual)

http://ymenvom.crestec.nl/new/manuals/M1C331_1.PDF

 

 

 

shift stopper needs tobe updated to the 2008+ yz125 the older ones cause problems like you are talking about

http://www.thumpertalk.com/topic/512858-replace-your-shift-stopper/

 

 

If you are going to do this much work, I would do it right

 

rebuild crank, Oem is prone to melting, here is the 2008 i rebuilt a little while ago, the stuffers like to melt when run super hard

photo1_zps2a1162d5.jpg

 

these guys are the best I have seen, they cut cranks apart when they rebuild them to prevent distortion, and they fix the stuffer problems on the yz 2 strokes they explain it in this video

 

 

rebuild crank

new crank bearings

crank bearing seals

inspect gears and shift forks for wear

transmission bearings for smoothness replace it needed

inspect clutch basket, inner and outer hub, clutch plate thickness for minimum wear tolerance (buy a vernier caliper very good tool to have)

new topend (wossner or wiseco would be my choice, dual ringed if you go wossner piston)

new piston pin bearing and C clips

 

 

And when you assemble the crank into the cases, heat the crank bearings with a torch, and put the crank in the freezer overnight. Everything will just fall into place with zero effort. Its the easiet and best way to assemble the crank into the cases because it causes zero crank web flex/distortion.

Edited by adam8781

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I got the right side cover and cylinder off, may try to split the cases tomorrow. 

 

Can anyone give me advice on this cylinder? It was replated at the last top end, I can still see the cross hatching and it should clean up even better. There is a shinny spot between two ports, does it look the plating wore off here? If so will it be safe to run for another top end or could it be a problem? I want to put my money into the bottom end now not the top.

 

Thanks 

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I got the cases split and I wasn't able to find any free lance ball bearings from the shift stopper. I found some minor metal shavings at the bottom of the case. Some transmission gears appear to have minor chips on top of the teeth (see pics). Should these be replaced and how do I tell which gears need to be replaced? 

 

I also found a spot behind the bearing that the clutch shaft rides on that appears to have been chewed up by a ball bearing, not sure if I need to do anything about that either.

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is that debris only or is there rough edges in that area of the case? that's not a good thing because one of the tranny bearings is pressed in this spot. i had an 04 kx 125 that had a bearing fail in that spot and it messed up the case to where i just got a new one. it also looks like that what broke in the tranny went through the gears.

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is that debris only or is there rough edges in that area of the case? that's not a good thing because one of the tranny bearings is pressed in this spot. i had an 04 kx 125 that had a bearing fail in that spot and it messed up the case to where i just got a new one. it also looks like that what broke in the tranny went through the gears.

Rough edges however the bearing that came out is smooth and feels fine. The actual rough edges are below the point that the bearing sits in so its not making contact with it, think it will be alright? Attached are two more pics.

 

Thanks

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doesn't look like it will be a problem but those two nicks on the outter edge aren't good but don't appear to pose a problem.

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How do you remove bearings and install them properly when you cant beat them out from the other side? Is there a special press and puller for this? 

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Yes you need a blind bearing removal tool that will go small enough has like a slide hammer attachment to it, I had to order mine from pit posse couldn't find anything local that went small enough. Makes popping the bearings out super easy and quick!

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Yes you need a blind bearing removal tool that will go small enough has like a slide hammer attachment to it, I had to order mine from pit posse couldn't find anything local that went small enough. Makes popping the bearings out super easy and quick!

Thanks man, how about installing them? Tap them in with a socket that fits around the outter edge? 

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No I used actual bearing/seal installing tool on the bearings looks like an impact wrench but has different size like washers you bolt on. Harbot freight i I have the larger size set and a smaller set they put a more even load on the bearing unlike a socket can. Socket surface is thin or doesn't contace the face of the bearing enough you could damage the bearing race doing that.

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No I used actual bearing/seal installing tool on the bearings looks like an impact wrench but has different size like washers you bolt on. Harbot freight i I have the larger size set and a smaller set they put a more even load on the bearing unlike a socket can. Socket surface is thin or doesn't contace the face of the bearing enough you could damage the bearing race doing that.

Picked up the bearing installer and puller. Is it more ideal to freeze the crank bearings and heat the case when installing or is driving them in with the tool just as safe? 

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