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01 yz250 motor into alum frame?
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2001 stock pipe will not work on alum frame. Bend is too tight and close to the bigger frame.
2001 stock carb will work, but the TPS is oriented 180 degrees opposite which prevents being able to rotate the carb on the bike to facilitate needle changes.
They may be externally identical from about '99 onward.
Sorry I can't be certain, but I think 2001 would fit just fine.
The Shop
The rear swing arm bushings will need to be enlarged ever so slightly when using a 99-01 motor to fit into the 02-21 bikes with the larger swingarm pivot bolt. If you have a drill press, easy to accomplish in a couple of minutes. There is plenty of material in the bushing to allow this. You can't simply swap the bushings, as the outside diameter of the 02+ bushings is larger than the outside diameter of the 99-01 bushings. This is really the only thing you need to do, and it isn't a big deal.
Only other significant changes to the bottom end (and they don't affect the use of the early cases on late model bikes) was the crank and kickstarter shaft. The crank used a different taper on the flywheel side from 99-00, 01-02, and 03 on if I remember correctly. Just need to ensure you use the same gen flywheel that matches the crank. Any year crank with fit in any year case from 99 up.
The inner diameter of the kickstarter shaft didn't change where it fits into the center case, only the outer. So you just need match the outer case to what ever generation kickstarter you already have... ie your kickstarter and outer clutch side cover.. easy.
Bottom line between your cooked motor and an 01, you will have all the parts to put it back together again. I've used multiple 99-01 cases building 02 + motors.
They won’t fit, unless you machine the earlier cases to fit the newer bushings, or turn the newer bushings on a lathe to reduce the outside diameter. I’ve seen this claimed on thumper talk a number of times and believed it until I did my first motor with older cases and had both generations bushings out to examine them.
There is however plenty of material in the earlier bushings to drill out the larger inside diameter. This is only way to approach it. Drill them out and be done.
I just want to confirm a few things with you guys before I order my new crank, bearings etc and start putting this thing back together. What I've ended up with is crank cases, cylinder, cylinder head, and power valve off of 99 model yz 250's that are in pretty good shape. Other than those pieces, will EVERYTHING transfer over from my '16? Including bearings, gaskets, seals, piston, etc etc. I'm gonna be ordering all new crank, piston, transmission bearings etc, am I ok just ordering everything for the '16 model year and expecting them to fit? I'm aware of the swingarm bushing and neutral switch, any other differences that I can expect along the way?
Thanks again!
Are your transmission bearings roached out after inspecting? I generally get significantly more hours out of mine than I see with the main bearings. Mains always get replaced with the crank, but transmission bearings always seem to last a long time. That's just a perspective of a middle aged offroad guy, fast young MX guy might have a different experience.
There appears to be a significant difference between oem bearings, seals, and gaskets... which I tend to use over some of the cheaper aftermarket parts or wrench rabbit kits. They certainly work and some folks are happy, but if I'm investing the time to rebuild I go oem for those. Just me, your experience my vary.
Good luck with your rebuild.
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