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84rm250

Spliting cases on my Yz426

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I'm spliting cases on my 02 yz426 due to broken valves and the shavings they left behind. Is there anything i should watch for or take very extra care doing? How hard is it really? I'v done 2 two strokes to replace crank bearings but never a four stroke. I'v already got the head and cylinder off due to the broken valves. I'm a Ase certified auto tech, and have been wrenching in the auto field for a few years now so i should have most the tools and common sense on how things work and how to fix them. My biggest worry is the trany, anything going to pop outa place the i need to watch for?

Any feed back from people who have split their yzf's open would be awsome, thanks!

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The tranny is basically the same as a two stroke so you should be fine. Just pay attention when you pull it apart so you know how it goes back together.

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I've split the case on my 426 to replace the transmission, and it isnt all that hard, just have to pay attention to where parts go, take your time and DO NOT FORCE ANYTHING!!!:thumbsup: (dont ask me how i know:bonk:) I cant stress this enough, if something wont go, there is most likely something in the way. Also there should be no flying parts when you split the cases. If there is, something is wrong.

I hope this helps, and good luck with that.:worthy:

oh, and happy trails! :ride:

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Hey Guys

Im in the same position of having to split and replace my cases. I got the motor out and tomorrow am planning to start tearing it down so i can replace my old cases. Any tips/ tricks you guys have will be greatly appreciated. I have the Yamaha manual. Also if anyone can give me a suggestion on how to clean the new to me cases before install it would be appreciated.

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Hey Guys

Im in the same position of having to split and replace my cases. I got the motor out and tomorrow am planning to start tearing it down so i can replace my old cases. Any tips/ tricks you guys have will be greatly appreciated. I have the Yamaha manual. Also if anyone can give me a suggestion on how to clean the new to me cases before install it would be appreciated.

Yamaha Manual:banana: :thumbsup: If you get stuck, follow the manual.:worthy:

I would use kerosene to clean it, but I'd be careful with the rubber parts..

Good Luck and Happy Trails! :ride:

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I would use kerosene to clean it,

Mineral Spirits is much closer to real shop solvent, and is a better choice. Commonly available at paint and hardware outlets.

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Alright ill pick some mineral spirits up today, would a plastic putty knife work for taking the old gaskets off? after i clean it with mineral spirits should i rinse out any residue with oil?

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1) would a plastic putty knife work for taking the old gaskets off? 2) after i clean it with mineral spirits should i rinse out any residue with oil?
  1. Not very well, no. Get a pack of the box cutter blades that look like old school razor blades with a piece of metal rolled over the edge. Use them carefully.
  2. No, just let them dry. Wipe the sealing surfaces down with brake parts cleaner just prior to assembly.

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excellent, thanks for the info so far guys. Today i also had to change the oil and tranny fluid in the jeep so i didnt make it as far as i would like. Im at the point of taking off the clutch boss so im going to find out how to make a make shift holding tool then hopefully tomorrow i should have the dissassembly complete. On a good note i just recently bouht the bike and the cylinder still shows cross hatching from a recent hone. Is is possible for me to keep the piston,rod, and crank all togeher while doing this case swap or should i remove the piston and wrist pin? Also when i get to the point of having to swap the transmission over is there any short way to do it or do i have to take each piece out individually and re install them in the new case in the same fashon? Thanks again for your help.

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I would just buy all the case bearings new - there's NO WAY you will be able to move them over without some form of damage to the bearings - everything else will just move over after you install the new bearings in the case halves.

Cylinder sounds fine.

Not sure what you mean about a "shift holding tool" If that's supposed to hold your drum, forks and gears together during the move to the new case - just wrap it in twine and be done with it.

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The new case halves i have already have bearings in them and they all are in mint condition. For the "Shift holding tool" I think i was mis-understood. Im going to make a clutch boss holding tool in a make shift fashion, meaning "a temporary substitute". Now if i can find some OEM gaskets close to home here in the middle of nowhere Canada I will be cooking with gas

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... there's NO WAY you will be able to move them over without some form of damage to the bearings -

That is simply not true at all.
The new case halves i have already have bearings in them and they all are in mint condition.

Im going to make a clutch boss holding tool in a make shift fashion, meaning "a temporary substitute".

If you have access to an impact wrench, you won't need the holding tool.

Pay particular attention to the condition of the mainshaft left bearing and the balancer shaft bearings. When you wash out a used bearing with solvents, they may feel gritty and rough, and this may be either an indication that they are still nice and tight, and actually do have micronic particles in them, or that they are actually damaged. Oil will usually make them feel OK again, but you must do what you can to determine what condition they are really in.

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One of the bearings can't be accessed from behind, so he'd have to use a puller that puts pressure on the inside race - no way would I use that again.

He doesn't have a press, so getting the rest out - even with heat is questionable at best - I'd pay the 80 bucks to replace them all - just safer and simpler - of course - he's already stated the new cases have perfect bearings so it's redundant.

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One of the bearings can't be accessed from behind, so he'd have to use a puller that puts pressure on the inside race - no way would I use that again.

He doesn't have a press, so getting the rest out - even with heat is questionable at best - I'd pay the 80 bucks to replace them all - just safer and simpler - of course - he's already stated the new cases have perfect bearings so it's redundant.

I'd pay $80 to do that, too, but the 8 bearings involved cost more like $200. If you have a late 450, the two balancer bearings alone are $140. The left mainshaft bearing (the blind one you referred to) is only $18, though.

There is a right and wrong way to extract or install bearings, of course, and if one was to use a slide hammer type of blind bearing puller, which would impart a series of impacts to the inner race and the rolling elements, that creates a potential for damage and an eventual failure. A pressure screw type is much less likely to do this, and in combination with heat, it is a good solution. That particular bearing can be removed without ever touching it by heating the case and slapping it against a solid surface face down, and since the case here won't be reused, one has a lot of leeway to work with in the regard.

My point is that an admonition such as the one you made is incorrect information in a general sense, so I'd rather it was not offered in the context in which it was given without some counterpoint. I have removed and reused literally hundreds of bearings of all kinds in all kinds of mechanical assemblies, and there are certainly rules to be followed and hazards to avoid, but to say that it should never be done is just not true.

On the other hand, you can't cut corners if you expect the engine to last, and if there is a reason to replace a component, it should be done.

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Ok, I can see blasting me for saying it can't be done without damaging them, I just don't like using anything questionable - since it's sometimes tough to know what shape a bearing is really in - I don't mess around with them, I'd just rather replace them for peace of mind

The last bike I did from the case up, I got all my bearings from a local bearing shop and the cost was less than half of Yamaha 's cost. I have a tendency to do this for wheel , steering head and swingarm/linkage bearings as well since OEM or aftermarket tends to be overpriced.

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Ok, I can see blasting me for saying it can't be done without damaging them, I just don't like using anything questionable - since it's sometimes tough to know what shape a bearing is really in - I don't mess around with them, I'd just rather replace them for peace of mind

The last bike I did from the case up, I got all my bearings from a local bearing shop and the cost was less than half of Yamaha 's cost. I have a tendency to do this for wheel , steering head and swingarm/linkage bearings as well since OEM or aftermarket tends to be overpriced.

That will work for about 80% of the casse bearings in this bike unless your shop has a good lead on them. The main bearings have a retainer groove ground into the side of the race and as of yet I have not really found a "bearing house" source for them.

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That will work for about 80% of the casse bearings in this bike unless your shop has a good lead on them. The main bearings have a retainer groove ground into the side of the race and as of yet I have not really found a "bearing house" source for them.
In the '06+ Gen 2 450, the balancer bearings are a proprietary custom size, and are stunningly expensive (retail $95 each). I found one bearing house (of the dozens in the San Diego area) that could buy them, but they were more expensive than what I could buy them at a discount for.

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i own a 426 and the bottom oil drain bolt has been taped out soooo many times that next time it strips i need all new casing and the dealer said its over $1000 for it but $2000 with labour, i like that bike and ive already put $2000 into but is it worth selling the way it is or should i get the new casing and still own it???

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