YZ426 Cases will not split


i have searched through the existing threads and cant find any help on this one.

I have removed all case bolts (all 12... please tell me if there are more!)

The cases are coming appart all except just in front of the bore. (i will post a picture later) It is where the front/top bolt is located. I have looked at the manual and I think there is a dowel pin where the bolt is.

If this is ceased, what is the best way to separate it?

Thanks for all the info TT.



Where you are pointing at in the diagram where a dowel is located it is actual a sleeve that the front motor mount bolt slides through I worked like Hell to get my case split, here is what I did if you can get it just the smallest amount open spray the shit out of it with wd-40 take a rubber mallet and hammer it back together, do this repeatedly I did it for about an hour open spray hammer, over and over again, (also spray it from the inside of the motor mount bolt hole) finally once you get it opened up a little more use a screw driver to wedge between the cases do it carefully so as to not score the faces of the cases. You have to do this at two point one right where the sleeve is and at bottom of the case near the tabs after prying at these areas pry at the back of the case don't get the back end opened up wider than the front, if you do you are working against yourself at that point, (your binding that already stubborn sleeve at this point). I managed to get the area at the sleeve opened pretty wide then went to the back and opened it and pop it came apart. It took me seriously about 2.5 hrs of working it open spraying hammering etc etc. When you finally get em apart you'll see that the sleeve will probably be discolored from corrosion, sand that bastard clean and put some anti seize on that sob. Hope this helps.

Thanks heaps for the reply. I suspected that there was some sort of sleeve/dowel that had ceased. It appears as if it has split, but still stuck together. I will load it up with WD40! I'll make sure its clean and oiled up before it goes back together!

The rear end of the cases are coming apart fine...

Thanks again.


Cheeze13 gave you some good advice. I was expecting a huge battle with my 2000, but it practially fell apart. I only had to stick a large screwdriver between the tabs and barely give it any pressure. My motor has been coming apart real easy except I stripped one of those damn hex screws on the main bearing holder.

Why are you splitting it?

Cheeze, hows yours coming along?

4th gear is screwed! It had been "slipping" so to say, but it has gotten really noisy... i suspect there are some very damanged teeth!


I still cant get the thing to split..... Used heaps of WD40 but it just dont budge.... anymore ideas?




Has it opened up any at the sleeve?

When I split the cases on my 426 I couldn't get them apart either. I seem to remember finding a "hidden" case screw. Maybe on the right side behind the counter balancer? :)

Sorry I can't remember exactly where it was :)



I should have looked at the diagram before posting.

I'll take alook at my bike and see if it jogs my memory.


I might be pissing in the wind but I had a swingarm bolt stuck on my yz250 one time. The bolt had seized on the aluminum on the motor. I went and bought this stuff call aluminum bright by duragloss and laid the bike over on the side and sprayed all i could down into the threads and it ran into the hole. Sprayed it off and turn the bolt and came out no problem.

I also am putting intake gaskets on my truck today. Sprayed this stuff on the aluminum intake and sprayed off. Bright and shiny. No gasket removal or anything. What I think happens is that water and what not gets on the aluminum and corrodes it causing it to sieze.

Also if you have mudstains on your hubs or motor spray this stuff on and spray off with water and it will look brand spanking new again. Try it. :):)

No..... The Damn thing still hasn't dudged! i have soaked it with WD40 for days and it still hasn't parted.

I might have to hit it with some heat..... i just want to get it apart so i can get some new gears and get back on the thing!

Thanks for the help.



The right crank half may be stuck in the bearing. When you split the cases the crank is supposed to stay in the left half.

You may try threading the main nut back on and giving it a solid thwack w/ a dead blow as you apply pressure to the cases w/ a small prybar or something.

Be careful...

i dont think that is the problem. the rest of the case is parting.... its just the small section at the top that will not part.....

i think the gas might have to get involved this weekend....


I seem to remember there being one bolt near the top that was recessed back further than the rest. At first glance it didnt even look like it had any part of holding the cases together, but it did. Clean any gunk off of there and have another look.

i dont think that is the problem. the rest of the case is parting.... its just the small section at the top that will not part.....

i think the gas might have to get involved this weekend....


Well, that's good. It is better if the hammer doesn't get involved.

I had a "mystery" case screw that I didn't find initially when I did this, but as I recall it was behind the barrel.

At any rate you counted the screws on the fiche and that is how many you removed...

Don't be like me, be careful and patient, new cases are spendy.

Anywho, as already mentioned earlier in this thread, I think there is a large dowel just in front of the barrel that serves as a coolant passage, no? Not hard to see how this could be corroded and sticking.


i finally got the cases apart today!!! Hooray! The sleeve where the front mounting bolt goes was ceased. I will clean it up and make sure there is plenty of oil on it before it goes back together!

4th gear on the drive axle is a bit of a mess. 1 complete tooth smashed off and 1 either side is badly damaged too. Dogs dont look real health either.

I will pull it apart further, but i think i will replace damaged gears and all shift forks just to be safe! cant be stuffed doing this again... well not for a while!

Thanks for the help!


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