Hybrid YZ450/WR450 Desert Gearbox ('06-'09)

I finally had the time, money, and ambition all at the same time, so while I installed a new piston in my '06 YZ450, I split the cases and swapped out 4th and 5th gears for the 4 and 5 from an '08 ('07-'11) WR450F.  It was a straight, simple bolt-in operation in every respect, and except for the 3 snap rings that one should replace, the 4 gears themselves are the only required parts outside of gaskets and the like.  The original shift forks get used if in good condition.  Nothing to add.


It works out extremely well in the open desert, too. The ratio spacing through the  first four gears with this setup is the same as the '03-'05 four speed exactly. Then, there's a nice step up to a real 5th gear that you can run with.   I was breaking in the new top end so I didn't want to run it too hard in the first place until after an oil change, and the lake bed was cobbled pretty badly by all the recent rain, but I hit 76 mph with not much effort at all.


Shifting through the gears with a YZ450 5 speed, the gaps get progressively tighter as you shift; 1-2 is the widest, 2-3 is closer, and so on.  This works good on the track because the top 3 are close enough that if one's not quite right, the other will be perfect.  But out in the more open environs of the desert, it's like there isn't enough difference between 3rd, 4th, and 5th to bother with.  With the WR top two gears, the gap between 3rd and 4th is about the same as between 2nd and 3rd, with the 4-5 shift being a little wider again.  If anything negative can be said about it, the biggest mental adjustment to be made is to remember to go fast enough in 4th to make 5th usable.


But it pays off big when things flatten out.  The bike will now cruise fire roads at 55-60 easily without revving the engine beyond its comfort zone, and it's no longer necessary to twist the thing to its limit on long runs over lake beds and such.  With the Rekluse clutch to make up for the tall first gear, it's a near perfect ratio set for the kind of riding I do.


The part numbers for the WR 4th and 5th are:


4th pinion: 5TJ-17141-20-00

4th wheel: 5TJ-17241-20-00

5th pinion: 5TJ-17151-20-00

5th wheel: 5TJ-17251-20-0


The same swap can be done to the '10-'13 model YZ450 as well, but that requires a new output shaft from the earlier '06-'09 model along with the gears.

Just out of curiosity and for possible reference what sprocket combo are you running and do you think it will stay the same? To bad I just caught this, I just buttoned up and fired up my buddies 08 tonight that dropped a valve and took all but the cases out. O well next time around.

13/48.  I might go back to the stock 13/49 when this set wears out.  Dropping the tooth at the rear was something I did for a little extra speed, but I don't need that anymore.  Then again, I might leave it like this.  I'm pretty happy with it overall.

I've also found the WR gear swap to be beneficial in the offroad setting. I went ahead and swapped all five gears instead of just 4th and 5th for a couple reasons: One being that I encounter a lot of slow 1st gear obstacles and the other being that the worn out dogs on the 2nd and 3rd gear in my stock transmission were beginning to cause shifting issues. I imagine a auto clutch would make the taller 1st gear for offroad much less noticeable.


I went with the 13/50 gearing combo (I believe the same gearing as a stock WR) and have only tried a 14/48 combo, so I can't speak on other combinations, but the 13/50 seem to work well for 95% of my riding and racing. Once again, with all the slower speed obstacles I encounter, this gearing allows 1st gear to be plenty low enough, without taking away any of the advantage of having the taller 5th gear. Also, when I do go to the motocross track, the gaps between gears seem to be spaced pretty well. If I were doing more fire road and open riding/racing (ex:Vegas to Reno), I'd be running taller gearing.


I agree the 4th-5th gap with the WR gears can seem a little wide, especially if you are in a sand wash. Waiting a bit longer to shift seems to work fine, and I'm sure a variety of performance mods could help close that gap for those who would want it.


I've had this swap for a few years now and really enjoy the benefits. It's nice in a race with any open stretch, or trail riding where you want to cruise without revving the engine.

I did the 4th and 5th wr swap as well when I did my last crank. 5th gear now is great for fire roads and faster tracks.

I can see why they use the Yz ratio 5th for mx, but for offroad the WR 4th and 5th is the way to go.

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