Rebuild bottom end?

guyanimal · Feb 14, 2006

I am a brand new user. My 15 year-old son finished his very first mx race Sunday. 10 feet before the finish line his bottom end blew, but he did cross the line. We bought his '97 RM125 last summer, so we expect things to go wrong. I am a reasonable tool handling kind of guy but have never opened or worked on the bottoms and am fairly new to 2-strokes. I was hoping to make this a cool dad/son kind of project.

We pulled the top end off and found that the lower connecting rod bearing is apparently frozen to the crank pin.

Here are my questions: Can we reasonably expect to do some or all of this work ourselves or is it the kind of thing that demands prior experience? Which special tools do we have to buy (crank case separator, etc.?) Is it worth it, in other words, should we just send it to an experienced mechanic?

Thank you very much.

xprojectstevex · Feb 15, 2006

I have never done a bottom end either but I am getting ready to. If your mechanically inclined I think you will do Ok as long as you have the service manual. You might want to get the "Clymer" brand manual, it's alot more detailed than the manufacturer manual. The manual will also tell you what special tools you will need so I would spend $20 on that before you go any further. I know for sure you will need to buy a case seperator($180 suzuki brand), clutch hub puller($50 for a universal one), and a seal press for the tranny seals(no idea on cost). I found a rm250 bottom end on **** for cheap, you might want to look on there for a 125 bottom and either keep it just in case you F**K up the one on the bike or just for parts and experience taking it apart before you dive into this one. Keep me updated on here and I'll keep you updated on mine so we can compare notes.

nickyd · Feb 15, 2006

it depends. if you grab a manual and take your time anything is possible. and you can do most of the work and farm some out if you can find someone to do partial work (some shops want all the work, not piecemeal). Plus your time frame will be longer if you do it yourself vs having a shop do it. You can get the cases apart by tapping with a mallet - check eric gorr's website - there is a section on two stroke technology that will map it out.

TimberPig · Feb 15, 2006

Here is what you need to know

Lower End Rebuild

Crank Rebuild

read those links, and it will answer your questions.

guyanimal · Feb 16, 2006

xprojectstevex said:
I have never done a bottom end either but I am getting ready to. If your mechanically inclined I think you will do Ok as long as you have the service manual. You might want to get the "Clymer" brand manual, it's alot more detailed than the manufacturer manual. The manual will also tell you what special tools you will need so I would spend $20 on that before you go any further. I know for sure you will need to buy a case seperator($180 suzuki brand), clutch hub puller($50 for a universal one), and a seal press for the tranny seals(no idea on cost). I found a rm250 bottom end on **** for cheap, you might want to look on there for a 125 bottom and either keep it just in case you F**K up the one on the bike or just for parts and experience taking it apart before you dive into this one. Keep me updated on here and I'll keep you updated on mine so we can compare notes.

That sounds great . . . we do have the Clymer manual. Tonight I pulled the motor out and we are going to take it to a race tech we were referred to. He is going to assess the damage and we will see where to go from there. I have the bearing/hub puller already. I did find out the case separator costs about $150 and Suzuki is back ordered.

guyanimal · Feb 16, 2006

nickyd said:
it depends. if you grab a manual and take your time anything is possible. and you can do most of the work and farm some out if you can find someone to do partial work (some shops want all the work, not piecemeal). Plus your time frame will be longer if you do it yourself vs having a shop do it. You can get the cases apart by tapping with a mallet - check eric gorr's website - there is a section on two stroke technology that will map it out.

Eric Gorr's website is great. Thanks for your help. I am going to wind up doing some of the work and having a race tech do the fancy stuff.

guyanimal · Feb 16, 2006

TimberPig said:
Here is what you need to know

read those links, and it will answer your questions.

Good stuff, thanks a lot.

skiboyracing · Feb 18, 2006

I just split my 250. I bought a clymer manual and although I haven't gotten all the parts to put it back together, it's been pretty easy. No special tools. I used a 2 jaw puller to yank the flywheel off, I bought two 3.25" bolts that thread into the stator bolt holes and used my 18 dollar harmonic balancer puller to split the case. I did take it to a local shop and paid 3 dollars to press the right side of the crank shaft out of the case though. Then for the bearings I sat the case in front of the salamander and heated it up. Most the bearings fell right out, I had to wack the mains a couple times but no big deal. The shift drum bearing I went to autozone and used their blind bearing puller for that one. That was free. So you can see with a manual and some cheap tools it's not hard or expensive. For putting it back together I went to a local shop where they let me use the lathe and made two aluminum slugs that fit into the middle of the crank bearings. I will install them and heat the bearings through the slugs and freeze the crank and I hope the crank and two halves slide right together. Read the manual and search this board. That is all I did and so far I'm not only surprized at how smooth it's going, but am having fun doing it as well. It will be a great learning experience for you and your son. Wish my son was old enough to help out and learn.

Oh and don't look at the schematics and get scared. It's not that bad. The transmission gears all come out as an assembly. There is more to take off on the outside of the case than there is once you split it.

rockers109 · Feb 19, 2006

I rebuilt my bottom ends several times. I do it once a year even if it seems OK. It's actually pretty simple with some tools. Check **** for a blind bearing puller. As for the crank don't bother trying to take it apart or put it together yourself, let a shop nearby do it for you. That's something not worth the chance to do it yourself. Good luck

skiboyracing · Feb 19, 2006

Speaking of cranks.. I agree. We've done it ourselves with a press, dial indicator, and some V blocks but it's a PITA. I bought my HotRod crank assembly for 169 dollars from motosport.com as part of a lower end kit. I would have paid 70-90 for a rod kit and by the time you add labor to install the rod kit in your stock crank, you might as well just buy the hot rod crank assembly and be done with it IMO.

Badgadjit1 · Feb 20, 2006

i blew my inner rod bearing out a while ago and got quoted on what it would cost to rebuild it, was around 300. So i found a hot rod crank for 175 and went that way.. Works great. Also if your comfortable with e.bay thats another way to go.

Rebuild bottom end?

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