wr 450 exhaust cam in a 426

Did anyone install the auto decompression exhaust cam in their 426? Anything else I should know before I order the cam and associated gaskets?

Check the YZ 450 forum and look for the longest thread. Yeah it's been done a bunch of folks. The guys down under in Oz are running some high mileage with this Mod with no problems so far. There are issues to consider. Read the post.

If I read you correctly, you want to put a WR450 cam in your WR... we have all put in YZ cams so far... because they were available... The WR cam will probably be best run as WR timed... rather than YZ timed... If you look through the 250 forum, they have discussed the reasons, but basically the Auto-decomp activates at a different point if the YZ cam is put onto WR timing, or the WR cam is put in as YZ timed...

Go look at the YZ4xx post... it is pinned to the top... and then if you want more info, the 250 guys are doing it as well, but without the sprocket issue like the 450 cam///

To save you some time, here is the PDF file


Have a look at that, then read the posts, then you will have an idea of what we are all doing... I have no problems with mine... only positives... easier starting and more power the main ones... :):D who can argue with that...?



I have just installed a 2003 YZ 450 cam in my '98 WR400, and it starts like a dream. With my JamesNow insert and the new grind on this cam, generating low end "BRAP!"; and the starting of the machine is simply unbeleivable. Did I mention that?

Maybe a bit of a BUZZKILL for new 450 owners (They are still getting an awesome ride) but the 400 still belongs in this forum!


To answer your original question, I ordered the cam, got it, installed it and measured the valves, found the exhaust valves to be .20 mm out, traded my 190 shims for some 210's, put the bike back together, and it has been nothing but smiles since. Riding in first competition tomorrow.

I left the original auto-decomp stuff on the bike because my hot-start button is mounted on the frame ('98 :) ), so I still could use that system to "clear it out" after a fall.

Will report back after Sunday.


In what ways did this alter the power characteristics of the 400? Does it kill top-end and does it soften the hit? Personally I love top-end and I love a hit. Power that is too linear makes for a boring ride (IMO). Does anyone know what the specs are of the YZ450 grind? It sounds like a fun mod but I'd like to have a base understanding of what to expect before I consider doing it. Keep us posted.


There is more bottom end, more top and less of a hit - they seem to have taken out the midrange spike by bringing bottom and top up to match... there is just a lot of power everywhere... It is more linear, for sure, but there is plenty of power to excite you in any gear or part of the rev range...

The JamesNOW! just adds to the bottom end...



Does it work ok with the stock intake cam or should it be changed to the 450 piece as well?


I left the stock intake cam alone, and simple changed out the exhaust cam, re-shimmed, and was done with it.

Race this weekend was dead engine start, hands on helmet. Bike wicked to life quick, but that was about all that I had going for me.... :)

As far as the power out-put is concerned, it really bites down low, and low end through mid range rpm's is where the bike is really pulling. Get up in the rpm's, and it seems like it pulls a little less than it did, but that is only by the seat of the pants.

If this makes no reliability changes to the machine, the change is worth it for the starting alone.

Hey BrandonW, How much did the yz450 cam/cams cost? This sounds like a great mod. :)

I ordered mine Monday for $112. I get a discount because they, Iowa City Motorsports, sponsor my sons. I think retail was @ $140. I did not order any shims since I do not know what will be needed until I do the install. We couldn't find a part number for the block-off plug for the old decompression cable, either.

I'm hoping David will fly halfway 'round the world to help... :D

In a very real cyber-way, he does that all the time! :)

Brandon, it is great to know it is working well in your '98. I, too, will use the YZ cam in my '99WR. Your, uh, 'race' didn't go so well..? Wasn't bike trouble, I hope?

Wish I was the globetrotting mechanic-to-the-stars I want to be... LOL with a suitcase full of jets, needles and valve shims...

The cam mod is simple... the worst part is having to make the second trip back to the dealer to get the shims once you know what size you will need... and as for the blanking plug, the same one is used in the YZ, so if your dealer has the Parts Fiche for the 03 YZ, then he should be able to locate the part number... I don't have the number off hand... but will look over the weekend and see if can I find it... then I will post it, and add it to the PDF file as well...

Just shoot me a PM/e-mail/carrier pigeon/distress flare if you need to... I can be a cyber mechanic at least... :)



You mean my "chase"? :D

I entered in the 4-Stroke Expert class, and was promptly fed my lunch.... Mmmmmm! Extra helpings too!

I primarily ride the desert, and the first race of the year was in the tightest woods that I have ever traveled. I could have had a two-speed gear box, and had no problems at all. But, 1.5 hours into the race, my shifter got stripped out. I was trying to downshift, and I was just in too high of a gear, and fanning the clutch to no end. I finally found out what the problem was, tried to tighten it up, could not, so I put my tail between my legs and DNF'd.

:D:):D :D :D :D :D :D :D

Funny part of the race though: The start was dead engine, with the waves going out like such: AA, then A, Vet Experts, 4 Stroke Experts, B Over and then B under. So, I am thinking that I will be on the course in front of the B guys, and if some of them catch me, they can push me along a bit, and I can learn some racin'. (This was my third race entered. Last year I did the Rimrock GP, Baja1000 and now this one.) So, about 10 minutes into the race, I got somebody on my pipe yelling that he wants by. Well, this ain't no enduro, so I don't really feel the obligation to let my man by. He put up with that for about 2 minutes, then I see a nasty pass headed my way. The woods were thick, and it seemed like you were smacking both ends of the bars at all times. Then, here he comes on the left hand side. I flinch a little, and that was all he needed. There was no mistake about where he meant to plant his elbow, and I think there was less mistake about whether or not he intended for me to end up in the trees. So, the next 4 or 5 minutes were spent wresting my bike out of the trees, but I actually did laugh about it. I also thought that maybe I need to reconsider my ideas about "holding the line."

It was all good, and I am back in the saddle this weekend at Horn Rapids....

DNF's will not be accepted!

For any of you new WR450 owners in SoCal that must have YZ timing I have a solution for you.

I have a new YZ450 Exhaust cam and I really want a WR450 exhaust cam. If you want to swap cams please send me a PM.

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