My 02 YZ 426F project

I picked up an 02 YZ 426F yesterday that I found on Craigslist for a good price. The PO had it lock up on him a few times, but it always freed up again and would run fine. Took it to a mechanic who pulled the side covers and valve cover off and found nothing obvious and figured the piston skirt had broken off and was the source of the problem. The PO decided he'd rather off-load this than fix it, and thats where I stepped in :smirk:

The bike as I received it:

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One hours worth of time got me here:

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and another 30 minutes got me here:

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So far the only issue with the chassis I have found is a rusted/stuck swingarm pivot bolt:

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I was able to drive it out without even breaking out the BFH but managed to booger up the threads while driving it out so I need to find a die to chase the threads.

Anyhow back to the motor- the head and valves look good, but the center intake valve appears slightly burned:

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Is this a normal condition or not? Onto the piston and cylinder- they look perfect. That's the good news. The bad news is the lower rod bearing has failed, which is why the motor would occasionally lock up. I know this photo isn't the best but:

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Are those heat marks on the crank adjacent to the rod normal or not? Now I get to self-educate myself on how to split the cases, and decide if I'm going to replace the crank assembly or just the rod and bearings.

I'm hoping to keep the cost as low as possible on this because there is a strong possibility I'll sell it when its fixed. However I have toyed with the thought of keeping this one and getting rid of the 450 because I've had such a love/hate relationship with it (more hate than love for the most part). Anyhow, if anyone has advice on how to proceed from here I'm all ears. If the cost of rebuilding the motor gets too high this will end up being parted out.

Are those heat marks on the crank adjacent to the rod normal or not?

That may be in the top ten most faq on these. Yes, the crank is heated by the factory during assembly, and the discoloration is the result. Every OEM YZF crank looks like this.

If you're suspicious of the big end, consider getting that crank rebuilt by Mr. Crank or another such outfit. 426 cranks are more expensive to replace as a complete OEM part than 450's. As far as the locking up thing goes, does the engine have an auto decomp cam?

That may be in the top ten most faq on these. Yes, the crank is heated by the factory during assembly, and the discoloration is the result. Every OEM YZF crank looks like this.

If you're suspicious of the big end, consider getting that crank rebuilt by Mr. Crank or another such outfit. 426 cranks are more expensive to replace as a complete OEM part than 450's. As far as the locking up thing goes, does the engine have an auto decomp cam?

Nope, still rocking the stock cam. I did forget to mention in my original post that there were some light marks on the intake cam- I wouldn't call it scoring (can't feel it with your fingernail) but visible marks on the cam bearings.

Any thoughts on using this rod/bearing kit? http://cgi.ebay.com/ebaymotors/YZ426F-WR426F-YZF426-WRF-ENGINE-CRANK-CONNECTING-ROD-_W0QQcmdZViewItemQQhashZitem5d2b6fa3ebQQitemZ400160695275QQptZMotorsQ5fATVQ5fPartsQ5fAccessories

I know that the illustration is not of a 426 rod kit. The rod big end is slotted, and the YZF has no small end bearing.

Don't know anything about the company.

Good news, just got off the horn with the local shop and they said for $100 they will rebuild the crank. Now to get the cases split and get the crank out! Nervous about doing it having never been into the lower end of a dirt bike before.

the good bad and the ugly of the 426 engine..it runs darn good usually lasts a long time but is very expensive to rebuild. it appears if you go thru the engine properly you will have a really nice bike ! slap the new AD cams in the rebuild budget:thumbsup:

splitting your cases is easy - just do a little searching on here for the tips and tricks to make it easy on yourself. That 100 is money well spent to get the crank rebuilt.

The vesrah kit is likely ok - the pic shows a 2t kit (Common thing that companies show one pic for all parts) but it states the right kit will be sent.

426 is probably the toughest 4 stroke out there and will outlast just about every other bike.

As for a rebuild expenses - it's no different than any other 4 stroke.

Problem gentlemen... I can't get the countershaft sprocket nut off. I've tried everything I can think of short of cutting or grinding it off. Impact wrench wouldn't budge it. Suggestions?

If you are not confident that your impact wrench has any real power, like a shop grade air wrench would, then you might take it past a shop, even a car shop and have them try theirs. I'll almost guaranty my half inch drive would take it off.

But you can, if you have an oxy/acetylene torch handy, also take a welding tip and heat the nut. The way to work it is to heat one spot on one wrench flat of the nut as quickly as possible to a red glow, then immediately hit it with the wrench again. The natural heat barrier caused by the joint of the nut and shaft will prevent the shaft from being overheated if you work quickly. The nut and lock washer will be ruined, of course.

Or, make one of these from an old chain:

http://www.parktool.com/uploads/thumbnails/uploads/products/ec5ebefa1d35cc0e8a8c1a161efff978df34a3df_430x390.jpg

Use a long enough bar (24") to match up with your biggest breaker bar.

I don't have an oxy/acetylene setup, best I can do is a hand held propane torch. My impact gun probably leaves a bit to be desired, but 90lbs and it wasn't moving at all. I also tried using an 18" breaker bar and still had no luck.

Maybe try some PB Blaster on it? Let it soak overnight and hit it with the impact driver again.

Maybe try some PB Blaster on it? Let it soak overnight and hit it with the impact driver again.

Tried that twice. No love. I did get it off finally though:

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I very, very carefully cut the nut with my Dremel tool on 2 sides as shown (it was a loss at this point... the impact wrench had rounded it off pretty well because I was using an SAE socket since I didn't have the correct size in metric). Tried to get it to turn holding the sprocket with channel lock pliers and using vice grips on the nut- still no go. I ended up taking an air hammer to what was left of the nut, hitting it on what was left of the nut near the edge of one of my cuts and it finally came loose. No damage to the threads either, phew.

A few more minutes and:

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The crank is at the local Yamaha dealer right now for a new rod kit. Still need to do some measuring on the piston/cylinder and check out the valves. I want to pull the transmission out just so I can say I've done it but it all looks fine.

I haven't been updating this, haven't been doing much either. I did knock some bearings out yesterday. One that needed to go was the one for the countershaft in the right side. Problem is that it is a blind bearing and I don't have a blind bearing puller. So, I rednecked one together that worked like a charm:

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Good work. :excuseme:

Now, here's an alternative. Just like Microsoft stuff, 90% of the time, it works 90% of the time:

Heat the otherwise bare crankcase in an oven with good temperature control to 250-275 ℉ (no hotter) for 20 minutes or more so that the metal is uniformly that hot. Using heavy leather gloves, remove the case from the oven and immediately slap it center joint side down fairly forcefully on a sturdy wooden surface. The bearing will often fall right out on the first drop. May take two or three. Let it cool normally until it gets down around 150.

Good work. :excuseme:

Now, here's an alternative. Just like Microsoft stuff, 90% of the time, it works 90% of the time:

Heat the otherwise bare crankcase in an oven with good temperature control to 250-275 ℉ (no hotter) for 20 minutes or more so that the metal is uniformly that hot. Using heavy leather gloves, remove the case from the oven and immediately slap it center joint side down fairly forcefully on a sturdy wooden surface. The bearing will often fall right out on the first drop. May take two or three. Let it cool normally until it gets down around 150.

I never thought of using the oven, I'll have to try that next time around.

I have the new bearings in the freezer waiting to be dropped into the cases, just need a few more bearings then this thing is going back together.

Freezing the bearing will help, but not as much as heating the case. Aluminum expands/contracts much more than steel does. Do both.

Line up the bearing without touching it to the heated case and insert it as straight and as quickly as possible. It will "seize" in the bore very quickly, but you may be able to bottom it bare handed. If it doesn't seat, work around the outer edge with a punch, or better, a tube that contacts the outer race only while it's still hot. It will go much easier than working with everything at room temps.

I was planning on putting the cases on top of the wood stove before trying to drop the bearings in. I suppose I could remove the one bearing that's useable and throw the cases in the oven for a bit :excuseme: Speaking of bearings, you don't happen to know if this bearing has a cross reference do you?

Yamaha PN #93306-20593-00

Its on the countershaft in the left side of the case.

It might. I haven't looked, though.

You can heat the good bearing to 275 without doing any harm to it. Just leave it there and clean/lube it well.

It might. I haven't looked, though.

If you get a moment, or can point me to some place I could look up the cross reference, that would be great. So far the only Yamaha bearing I've had to purchase is the crank bearing. That one hurt!

You can heat the good bearing to 275 without doing any harm to it. Just leave it there and clean/lube it well.

Good to know, thanks much!

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