03 YZ450 exhaust cam


16 replies to this topic
  • ksp

Posted December 01, 2004 - 07:21 PM

#1

I think I'm getting the idea by reading some of "YZ450 cam mod please read" but maybe somebody can verify, can you not put an '03 YZ 450 exhaust cam into an 01YZ426 due to cylinder head, cam shaft or cam chain design differences? Somebody I know is tired of playing with the decomp lever and the monotonous starting procedure. Any info would be appreciated. :cry:

  • yzf450jack

Posted December 01, 2004 - 07:35 PM

#2

there is a 450 cam mod section at the top of the page for lot's of info. you should go with a hotcams decompression cam :cry:

  • Satch0922

Posted December 02, 2004 - 06:53 AM

#3

The thread at the top of this forum explains it all. It takes alot of time to read so here is the short version. The 450 exhaust cam will work in the 98-99 400F and the 00-02 426F. Mine is coming up on 2 years....... it's like getting a new bike. The drill is totally unnecessary.....regardless of how good you get at it.

http://www.photonrac.../PDF/450cam.pdf

  • grayracer513

Posted December 02, 2004 - 09:22 AM

#4

The only thing "different" between the two engines is that the pitch of the cam chain is very slightly different. A lot of people have used the '03 OEM cam anyway, and by far most have had no trouble. Ideally, though, you would use the Hot Cams exhaust cam, since it's made to match up properly with the 426 chain.

Look through the forum. This is one of the best things you can do to the earlier bikes. :cry:

  • berudd

Posted December 02, 2004 - 09:50 AM

#5

As a 426 owner I have decided against this mod. My 426 is at least as easy to start as all my friends 450s. It is almost always a one kick affair. Most of them just try kicking the 450 over and over like a 2-stroke which is not the best way. One kick with my "routine" is quicker than 2 or 3 stabs at the kick starter. All 4 strokes start best if you first find TDC and nudge it just past this point first. That includes bikes with an auto-decomp cam. The 426 just requires that you do this. In addition, when I do do something stupid on the track and flood it, I can pull the lever and kick in 15 or so times to clear it out. I have heard though that you can retain the lever even with the autodecomp cam.

IMHO, this mod is nice but not a cure all for starting the beast.

  • Satch0922

Posted December 02, 2004 - 06:08 PM

#6

A lot of people have used the '03 OEM cam anyway, and by far most have had no trouble.



most? try NONE

  • Satch0922

Posted December 02, 2004 - 06:12 PM

#7

As a 426 owner I have decided against this mod. My 426 is at least as easy to start as all my friends 450s. It is almost always a one kick affair. Most of them just try kicking the 450 over and over like a 2-stroke which is not the best way. One kick with my "routine" is quicker than 2 or 3 stabs at the kick starter. All 4 strokes start best if you first find TDC and nudge it just past this point first. That includes bikes with an auto-decomp cam. The 426 just requires that you do this. In addition, when I do do something stupid on the track and flood it, I can pull the lever and kick in 15 or so times to clear it out. I have heard though that you can retain the lever even with the autodecomp cam.

IMHO, this mod is nice but not a cure all for starting the beast.


While the above statement is true, I have never heard anyone do the mod that wasn't thrilled to death. If you decide not to do the mod that is ok too. I just have to tell you if you don't, your missing out. I will not go into all the reasons why the autodecomp set up is far superior......I as well as countless others have already given our testimonials in the 450Cam Mod thread. If you do the mod...you will LOVE your bike. IF you don't ....then it's business as usual. BTW...the other advantage to the OEM cam mod is the smooth powerband and decrease in compression braking....yes you can actually bump start the bike. This helps emensly on the track in case you lock up in a corner and stall ....you just let the clutch out and it springs back to life.....try that with a stocker.

Good luck.

  • ksp

Posted December 02, 2004 - 06:52 PM

#8

Thanks for all the input so far, the bike in question is not mine, I actually have a shop and work on bikes for people. I put an 03 YZ250F exhaust cam in an 02 WR250F, WOW! what a dream, it starts effortlessly about like a YZ 125. Just wanted to make sure that you can do it on the 01 YZ 426 in the same way. I also have an 02 WR 250 and don't have any problems starting it in the stock fashion so I will probably leave mine but if I was racing it I would do it in a second.

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  • blue_beast_wins

Posted December 02, 2004 - 08:08 PM

#9

While the above statement is true, I have never heard anyone do the mod that wasn't thrilled to death. If you decide not to do the mod that is ok too. I just have to tell you if you don't, your missing out. I will not go into all the reasons why the autodecomp set up is far superior......I as well as countless others have already given our testimonials in the 450Cam Mod thread. If you do the mod...you will LOVE your bike. IF you don't ....then it's business as usual. BTW...the other advantage to the OEM cam mod is the smooth powerband and decrease in compression braking....yes you can actually bump start the bike. This helps emensly on the track in case you lock up in a corner and stall ....you just let the clutch out and it springs back to life.....try that with a stocker.

Good luck.


Yes !!

  • grayracer513

Posted December 03, 2004 - 10:29 AM

#10

All 4 strokes start best if you first find TDC and nudge it just past this point first. That includes bikes with an auto-decomp cam. I have heard though that you can retain the lever even with the autodecomp cam.

IMHO, this mod is nice but not a cure all for starting the beast.


The way the YZF decomp works, the left exhaust valve is lifted as the compression stroke begins and is returned to its seat just prior to TDC. This was done to enable a small, lightweight starter motor to crank the engine, and it was necessary to close the valve before TDC so that the engine could actually start with the decomp active. When you use a kickstarter, the "Hard Spot" you feel is not compression, it's the piston trying to pull down against the vacuum formed in a closed cylinder. You roll the engine against that "hard spot", then reset the kickstarter and kick it from there, not push it past that point.

The decomp mod also allows pretty much 2-stroke-like bump starts without the need to manually use the compression release.

And, yes, you can keep the manual decomp in place. In fact, you can actually buy the whole thing in kit form from Yamaha and install it in a 450 if you want. I just have no idea why.

People who have trouble starting their 450s are usually victims of the "Never Open the Throttle" myth. No four-stroke, or 2-stroke, for that matter, is always going to start with the throttle in the same position under every circumstance. Most of the time, mine lies it cracked just over idle. When they are partly or totally flooded, they are going to want an even larger throttle opening to help clear the cylinder. The "don't open" warning is an attempt to keep people from doing the "twist-as-you-crank" thing that so many 2-stroke riders do. THAT is a no-no!

As a long time rider of the old time (late 50's to 70's) big thumpers, I was also skeptical about not having a manual compression release, but not any more.
:cry:

:cry:

  • berudd

Posted December 03, 2004 - 10:37 AM

#11

Oh, yeah, I was not trying to say people are not happy with it. I just don't think it is "manditory" as some folks claim. Since I have zero problems starting my bike, there is nothing to gain here. Smoothing the power? Well, I never felt it was needed but I can't really say without one with the mod to compare to. That may be nice. De-comp braking? Hmmm, again, no issues here. I have hoped off of mine on to an 03 450 and didn't notice a difference in this area. Bump start on the track. I can do it to. You just gotta pull in the decomp lever with the clutch. Let the clutch out first and it will go 'chug chug' once or twice and then release the decomp lever. I can do this down to some very low speeds. But the best option is not to stall it! :cry: I killed it in the air once by tapping (ok ok, MASHING) the rear brake. It was pretty weird sailing over a table top in complete silence!! When I hit the ground it fired up fine. The force of the impact is enough to turn the engine over without any decomp. There may have been a slight drag from hitting with a dead engine but nothing major.

My point with this mod is not that it does not work or that it is a bad idea. I still consider it from time to time, especially with cams that claim improved performance. I just don't think that you should expect it to cure any ills. If you have trouble starting it stock, then you probably will after the mod as well. Granted, I have gotten very comfortable with my stock set up, but if you take the time to do the same you will find that this is a very easy bike to start. If it is hard to start, make sure it had no mechanical woes before you start making changes.

  • Satch0922

Posted December 03, 2004 - 11:28 AM

#12

Smoothing the power? Well, I never felt it was needed but I can't really say without one with the mod to compare to. That may be nice. Bump start on the track. I can do it to. You just gotta pull in the decomp lever with the clutch. Let the clutch out first and it will go 'chug chug' once or twice and then release the decomp lever. I can do this down to some very low speeds. But the best option is not to stall it!



I suppose I should clarify that at this late stage of the game, the 450cam mod to make your bike a serious race bike is probably irrelevant. If you need a serious race bike then buy a 450. HOWEVER, almost two years ago when most of us did the mod, we were interested in making the 426 a serious race bike. I am gonna get one more season out of mine and then it's time for the 06.

Let's face it, no real racer is going to pull the clutch and decomp lever in at the same time to bump start a bike while in the heat of the battle.......just not gonna happen. If your a weekend warrior then I suppose it's not gonna matter if you stall it or have to grab three levers to restart your bike. Not trying to be snotty but rather realistic. Everyone I have ever heard say the decomp cam was not necessary was either not a serious racer or was afraid to tear into the bike. Yeah you can ride the bike in stock form as I did for a year....but why would you want to if there is a better way?

I would rather at this point advise anyone who is on the fence to NOT do the mod. HOWEVER...if you want an easier bike to start and ride, one that has smooth power all the way to the rev limiter and one you can start by hand (yes it's that easy and yes you will appreciate it on lap 4 of a race if you crash) you can have it for less than $120.

This is a old and tired subject seeing how the newest 426 out there is over two and a half years old.......however I still like helping people do the mod. PM me if you need info or "how to" advice.

  • mj2412

Posted December 03, 2004 - 02:38 PM

#13

Hy,

I know too god the feeling when you jump over a table with a YZ426 01 in completely silence. It happens twice to me at the same day and every time the engine starts again. Both time it was a hard landing because of the engine braking and the result was a broken 3 gear. :cry: I only can recommend that to start a YZ426 in this way is really bad for the bike. I also can understand that the forces inside the engine are huge when the engine will be started with the rear wheel.

Martin

  • Satch0922

Posted December 03, 2004 - 06:37 PM

#14

good point Martin!

  • jimn

Posted December 03, 2004 - 07:12 PM

#15

All I can say as a recent convert is,one week before the cam mod I ran my first hare scramble(I had the cam at home but knew I couldn't get the shims in time).It was on mostly tight rocky singletrack,I ,due to my advanced skill :cry: stalled a bunch of times.I can still see myself rolling silently down steep loose hills furiously upshifting in the hopes of a bump-start before the impending uphill.Unfortunately I only have around a 30" inseam so restarting on a ridge trail sometimes means pushing to a hopefully close,well placed high spot on the left side of trail so I could start the "drill".I'm pretty sure the cam won't improve my riding skills,but I bet it will cut down on the use of my advanced foul language vocabulary! :cry: Jim

  • blue_beast_wins

Posted December 03, 2004 - 07:41 PM

#16

I can assure you it will :cry:

  • grayracer513

Posted December 03, 2004 - 07:45 PM

#17

On the bump start thing, you brought up stopping the engine in the air. I was thinking of other times, for instance, when I braked it to death going into a tight downhill off-camber, and all I had to do was get off the brake and clutch it quick, and it lit right up. That kind of thing.

As I said, I know how to light a thumper off with the compression release, my Goldstars, Matchlesses, and Victors all had them. It's just so much simpler this way. That's all. :cry:





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