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Rebuilding a 98 YZ250

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I have a question for you Yamaha gurus. I'm rebuilding this 98 yz250 and its a basket case. The top end was ran way lean and melted down. The crankshaft seems ok to me but the threads for the flywheel are destroyed. I've found some wiseco kits on eBay that include a whole crank with rod and all bearings, a piston and whole gasket kit. The problem is I haven't found one for a 98. From what I have found in research it seems that a crank from a 97-02 is all the same. Is that correct? I'll include a pic of the kit I'm looking at. Any advice is appreciated. ImageUploadedByThumper Talk1458604208.715978.jpg

ImageUploadedByThumper Talk1458604229.705432.jpg

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I think I'll stay away from a wiseco crank. I see some people saying they aren't manufactured well enough to last. So I guess my question is, what years of crankshaft will fit the 98 engine?

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I don't know exactly what years interchange but I can tell you have the older engine. Same cases the 93-94-95 use. A little bit newer bike has the same engine cases as the current yz250 where the clutch cable enters the ignition cover.

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I see what you mean by looking at this pic. This one is a 99 according to the op of the thread. ImageUploadedByThumper Talk1458608569.860733.jpg

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I recently rebuilt a 95 yz, same bottom end as you. I had to rebuild the crankshaft using the original crank halves. I got a connecting rod kit from pro-x, and did it myself (fortunately I have access to a big press and killer dial indicators). Since you said your threads are messed up you might have to buy a used crank (check eBay) and then have it rebuilt.

My 09 yz has a wiseco crank, installed by the previous owner, with no problems so far. I think as long as you install it properly and use a quality oil, a wiseco crank can work just fine.

Edited by desrider891
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Dude I bought a 98 with little to no knowledge of what I had at the time. They are good bikes in my opinion but parts are twice as much and hard to find at a decent price used parts are either worn out or not worth it. My advice to you is get it running and sell it even if you lose a little cash in the end get you a 99 or higher 05 to present if you want the aluminum frame I promise you will not regret it

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How bad are the threads? Post a pic if you can, You may be able to clean them up with a thread file good enough to use again.

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I'll post a pic tomorrow. It's sitting on my bench at work. I filed them and chased the threads. It's not in good shape. I think someone tried to remove the flywheel without a proper puller at some point. I had trouble getting the nut off myself.

Edited by jhague86

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Just a small update: Got the piston kit to the machine shop and waiting for them to finish up. Ordered a set of crank bearings and seals. Still need to order an engine gasket kit and then it will be time for reassembly.

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Nothing like filing the ring end gap and getting ready to install the piston on the rod to realize the piston kit didn't include a wrist pin bearing and you didn't purchase one separately. Ordered one today, hopefully next weekend this thing will be Smokin' again.

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