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YZ300 WR Trans

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What do you guys think? I have a cylinder and looking at buying a bottom end off of Ebay.

This is gonna be a new project that I hope to be building this winter. I currently ride a YZ 250 with a 280 big bore kit and I love it. Been wanting to do the WR gear swap as well but now that I have been putting some pieces together, If I go ahead and do a full build, then I can just swap out motors and stick with the one I like most. Or keep them both so when I rid HM I can run the 300 and tight eastcaost HS I can run the 280.

Looking for opinions.

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I have the Eric Gorr 295 kit with full wr tranny! It's pretty AWESOME! I ride tight woods in Colorado, endurocross, and hare scrambles. Bike does great everywhere!

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I built a '05 YZ285 with the gearbox out of a WR400F. There was a big 'gap' between 2nd & 3rd that I didn't like. I sold the bike to a friend; big mistake. So, I decided to build my '03 backup into a YZ265-WR with Eric Gorr low-to-mid porting. This time I used 1,3,4 & 5th out of a 2002 WR426. Note that I kept the YZ 2nd gear. Much better gear spacing. Take a look at the gear ratios for the WR426 vs. the YZ250 and you'll see what I mean.

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That's great info. So by keeping the stock 2nd gear it closed up the "gap"?

Rule number 1: Never sell a bike to a friend. :smirk:

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I built a '05 YZ285 with the gearbox out of a WR400F. There was a big 'gap' between 2nd & 3rd that I didn't like. I sold the bike to a friend; big mistake. So, I decided to build my '03 backup into a YZ265-WR with Eric Gorr low-to-mid porting. This time I used 1,3,4 & 5th out of a 2002 WR426. Note that I kept the YZ 2nd gear. Much better gear spacing. Take a look at the gear ratios for the WR426 vs. the YZ250 and you'll see what I mean.

Interesting, I have never noticed a Gap from 2-3 in my WR equiped 265.

My engine is out of an 01 model where 2nd is slightly lower geared than the 03 models.

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hmm.. was thinking about putting wr 1 , yz 2,3,4 and wr 5th so it becomes a semi-wide ratio gearbox in my own bike. I have a wr gearbox i love the thing , but the gap between 2nd to 3rd can become a pain i sposse, specially when racing , i felt i could give the yz box more abuse when shifting fast.

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stock WR

29 12 2.417

26 15 1.733 gap 0.683

21 16 1.313 gap 0.421

21 20 1.050 gap 0.263

21 25 0.840 gap 0.210

WR with 2. from YZ

29 12 2.417

23 15 1.533 gap 0.883

21 16 1.313 gap 0.221

21 20 1.050 gap 0.263

21 25 0.840 gap 0.210

keeping the 2st from the yz will make the already to big gap between 1st and 2st huge.

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But you never notice the huge gap between 1st & 2nd. 1st is just a granny low; you never use it unless you need to crawl thru a creek bed or get thru some type of trials stuff. Keeping the YZ 2nd closes up the gap where 2nd becomes usable. If you are running a big bore kit you will never use the WR 2nd gear either; the rear wheel spins or you have way to much power to the rear wheel. In the example above notice how even the gaps are with this setup.

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depends of the riding style

- for hard enduro on gnarly terrain - Erzberg style (90% 1st or 2) the complete wr setup is better

- for higher speed trails the 2st from the YZ is a better option in the wr setup.

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stock WR

29 12 2.417

26 15 1.733 gap 0.683

21 16 1.313 gap 0.421

21 20 1.050 gap 0.263

21 25 0.840 gap 0.210

WR with 2. from YZ

29 12 2.417

23 15 1.533 gap 0.883

21 16 1.313 gap 0.221

21 20 1.050 gap 0.263

21 25 0.840 gap 0.210

keeping the 2st from the yz will make the already to big gap between 1st and 2st huge.

That is why I have never noticed the gap, I have 2nd from an 01 YZ which is lower than the later models.

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I'm not to concerned with 1st to 2nd but would like to have 2nd and up to not be so far apart that it's not usable.

My ultimate goal is to build this motor and put in the bike to maybe run some GNCC and my Hatfield McCoy trips. Maybe keep the current one for the tighter HS and single track stuff. Cheaper than buying and setting up another bike.

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For those that have not ridden the YZ with the WR tranny mod it would be hard to explain how well it works, especially if you're just using numbers to make your decision. I was pleasantly surprised with how well my 99 worked with the complete WR gearing, these bikes pull so well that it actually improved the delivery and was much more responsive to minor gearing changes (ie: one tooth on rear sprocket). I would like to ride one of the oversize YZ's with this change, I imagine it would be amazing!

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I read somewhere that when you put the full gear set in that you have to modify the cases to make first gear fit. Anybody know about this and or have specs and instructions?

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First gear needs the case relieved a small amount for clearance, just use the gear to mark the case while it is on the shaft then remove an amount about the thickness of your thumbnail with a dremel.

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That's easy enough.

I am gonna pull the trigger and do this. Going to start searching Ebay for the gear set. I will revive or new post with build pics

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Well, Here it is in many pieces. I have been looking for a trans but cant seem to find anything on ebay. Is it only the 426 trans or does a wr250 trans work? I have other sites up trying to figure out ratios.

I pulled it down to do a top end and found broken power valve and the cyl was starting to wear at the port. I figured I would do a crank while i'm in there. I have never had a reason to tear it down, and I have had it since 07

IMG_0382.jpg

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Yeap those trannies are hard to get nowadays, WRF 400 and WRF426 are the ones which fit. Good luck hunting.

If you can't get them you can order the gears new. Cost is about 300 I think.

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