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2007 YZ450 - WR Cylinder head assembly?

9 posts in this topic

I've been searching around the YZ450 forum for about an hour and haven't found my answer.

I just read in the new Dirt Bike about a pro off road racer (forgot his name) who made his CRF450R more rideable by installing a CRF450X head and cams.

I would like the milder WR cams for the type of off road riding that I do. I suspect that the YZ cams are what I dislike about this bike in really steep, slow, heavy clutch sections.

I've already added the heaviest GYTR flywheel weight and changed my gearing to 13-52 which made noticeable improvements in the slow sections mentioned above.

From what I read on TT the '07 WR cams will not fit the '07 YZ so changing the head seems like the solution.

I just looked at the fiche and noticed that the base gasket, head gasket, cam chain, and cylinder are the same part numbers for the '07 YZ and '07 WR.

Yamaha sells the WR cylinder head assembly that appears would bolt right on.

Besides the WR cams what else would I need to do this?

Thanks for any feedback/advice.

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From what I read on TT the '07 WR cams will not fit the '07 YZ so changing the head seems like the solution.

Where did you read that? An 07 WR owner swapped the 07 YZ cams into his WR to make the bike more potent (he races). It worked fine, except it woulldn't e-start - something about the location/timing of the decomp pin. However, it would kick start just fine. He went back to stock as the e-start was more valuable to him then the slight increase in power from the YZ cams. I see no reason why the reverse wouldn't work in your case. And, as far as running YZ timing with WR cams, most WR owners run their bikes that way (grey wire mod) with no issues.

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Maybe I'm misunderstanding grayracers post quoted below:

original link: http://www.thumpertalk.com/forum/showthread.php?t=667333&highlight=wr+cam

It used to be that the camshafts themselves were identical, and the only difference was that the WR exhaust was advanced. However, the '06 and onward YZ models have new cam grinds, and the '06 and later WR's have milder cams. If you wanted to, you could install a set of stock '05 WR cams in your bike, and that would make the engine run more stably at very low RPM's. But, it will still have higher gearing and less rotating mass than a WR, and I don't think you will find the loss of power worth what little you'll gain in return. The '06 YZF runs pretty well below 5000 with a heavier flywheel.

It sounds like the difference is the cam grinds but then gray recommends the '05 rather than '07 WR cams which confused me.

So the '07-08 WR cams will drop right into my '07 YZ? Is there anything else I need to be concerned with? Thanks.

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The cams will drop right in, it is just the lobe shape and timing that is different between the YZ and WR.

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It depends on what you want. The cams will physically fit into the YZ head, and they will improve the low speed operation of the engine, but it will not make it as smooth and chuggy as a WR, and it will cost you power. My recommendation of the '05 WR cam was made because it will cost you less power than the later WR cams will, but give a similar improvement in low speed performance.

The problem is that, besides the cam timing, there are still 3 other things that make the WR run as smoothly down low as it does, and none of them is the head.

>The WR has a much heavier flywheel than anything you can bolt into a YZ.

> The WR has a totally different ignition timing map.

> The WR has a lower first gear.

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Thanks for the info guys. My other winter plan is to drop in the WR transmission.

I install the WR transmission (45mph cruising speed doesn't work when riding with 6 spd ktms, and first gear is still too high for some of the CO trails I ride), WR cams, Moose lighting coil (I considered the WR crank/lighting coil but I don't need that kind of wattage), and new piston and ring since it's going to be apart and it's got 55 hours on it.

The bike right now is so close to what I want, I'm not looking for total WR power just some of the smoothness. I rode a friend’s WR and I would probably be posting questions on how to increase the hit if I owned a WR.

I will probably be happy with just the WR tranny, I just thought since it's going to be apart I might add the cams to possible gain some more grunt and smoothness.

Thanks again.

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It depends on what you want. The cams will physically fit into the YZ head, and they will improve the low speed operation of the engine, but it will not make it as smooth and chuggy as a WR, and it will cost you power. My recommendation of the '05 WR cam was made because it will cost you less power than the later WR cams will, but give a similar improvement in low speed performance.

The problem is that, besides the cam timing, there are still 3 other things that make the WR run as smoothly down low as it does, and none of them is the head.

>The WR has a much heavier flywheel than anything you can bolt into a YZ.

> The WR has a totally different ignition timing map.

> The WR has a lower first gear.

Gray in your opinion do you think the bike would run "strange" with the more aggressive YZ ignition map and less aggressive WR cams? Thanks.

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I don't know about strange, but it may be a bit weak.

I think I'd advise you to start by doing the trans and adding a flywheel like the GYT-R offroad unit. Then, if you still feel as if you want to alter the engine's power curve to smooth it out at lower speeds, use the exhaust cam from an '03-'05 WR, not because the newer ones won't fit, but because they are a different grind than the later WR cams, which are concerned more with emissions requirements than performance. I just think it will run better.

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