YZ/WR cams, is there a differance?

[doctorchopper]

I read somewhere that to get YZ timing on the WR's all you have to do is advance the exhaust cam one tooth, is this true? I thought the lobes on the cams would be different. Do you get harder hitting power with the YZ timing. I'm looking on ebay for a set of YZ cams, would I be wasting my money purchasing them?

[ISBB]

yes you would... the cams are identical... the only diffrence is timing...

The only YZ cams you would bennifit from are the new ones w/ auto decomp in them...

[eightballeddy]

the wr and yz intakes are the same, but the exhaust cams are different. The bike will rev much quicker and you will gain a lot of power up top by switching to the yz cam. I also heard that hotcams are awesome if you install both of them, but it's quite a big price jump. Do a search on this topic if you want. There is quite a lot of posts on this topic. I say go for it! ? This mod is for '03's and up. I heard that for the 426's you can just advance the timing by one tooth but i'm not positive. ?

[mousemeat]

on the 426's and 400's you only need to rotate the cam one tooth. on the 450's this would also be true if it weren't for the auto decompressor. So for the 450's you need to get the YZ one, because if you were to rotate the WR one the auto decompressor would be off. You can also add a 450 cam to an earlier bike to get auto decompression for easier starting.

[doctorchopper]

Ya it is a wr426, i should have notted this in my first post. Just wondering about loosening off the cam chain to advance the cam, is there a special trick on doing this? Also is it going to be a noticeable change in power delivery?

[eightballeddy]

You will have a lot more hit up top by swithcing to yz timing, but you may loose a little bit of the bottom end. I've heard of a lot of people switching back to wr timing because the power delivery didn't suit their type of riding. If you ride a lot of single track trails the power might be a little much, but if you ride wot a lot this would be a good mod for you ? . It all comes down to personal preference. If you're just advancing the cam one tooth why not try it to see if you like it. ?

[WheelsUp]

Don't you guys have auto-decompression on the 400 class bikes?

If you do, then you cannot change the timing by rotating the cam (you are actually retarding the timing, not advancing it).

On the 250s, you need to buy the YZ cam or the bike won't start properly.

[mousemeat]

manual decompression on 400 and 426

[deadcarnahans]

If you do, then you cannot change the timing by rotating the cam (you are actually retarding the timing, not advancing it).

Good point, Wheelsup.

Retarding the exhaust lobe will narrow the separation angle and improve top end, since the exhaust event occurs first.

I wonder if anyone has gone the wrong way, or, if anyone has experimented with the intake timing.

Is there any hidden low end torque available that we don't know about?

[doctorchopper]

I do a lot of road riding, so I think this weekend I'm gonna give it a try. How do you slacken off the cam chain so I can slip it one tooth?

[Cmott426]

Try this link

http://www.thumperfaq.com/yz_timing.htm

[doctorchopper]

Looks nice and easy to do, thanks for the link

[88 lover]

i have a 02 wr and i am interested in changing the timing to yz do i advance or retard 1 tooth?

[WheelsUp]

Looking at the sprocket side of the bike, you will rotate the exhaust camshaft clockwise by one tooth.

This is more often than not mistakenly referred to as "advancing" the timing, but it is in fact retarding it, holding the exhaust valve open longer, which has the effect of increasing the "overlap".

Increased overlap allows the exiting exhaust flow to assist in scavenging fresh fuel/air during the intake stroke.... not unlike a 2-stroke.

Some TTer years ago said that the YZ was advanced (we all know that advancing timing increases power, right? ? ), and ever since then it has been repeated.

[Rip Wheeler]

Ya it is a wr426, i should have notted this in my first post. Just wondering about loosening off the cam chain to advance the cam, is there a special trick on doing this? Also is it going to be a noticeable change in power delivery?

D/C, I had a WR426 that was YZ timed and I now run a WR450 that is WR cammed. I did buy a YZcamshaft for it, but after giving it lots of thought (and remebering how the 426 ran) I decided that me, trail riding, the WR cam was much better suited for me. I had the loss of low end, and the rela hard hit on the top, made nice power, but it was abrupt. Now with my "WR" timed 450, the power is nice and even, all the way. Makes it so much eaiser to ride trails. But some folks just like bragging rights of the extra power and can work around it. I did manage it OK also, but lower riding speeds (tight stuff) the WR exhaust cam or WR timed engine was best for me. If you race it on a track, or open desert, the YZ timing may be for you. Nice thing about chaging timing 1 tooth, you can undo it if you dont like it. Try it out ??