Top End Power Lost After 450 Cam Mod

[dirttrack25]

I just recently did the 450 cam mod to my 01 426. Today was the first day i have actually got to test it, and my results were different from others. I found that it actually wasnt THAT easy to kick and ALOT of top end power was lost, bottom was still OK but it wasnt all there and the power soon fades in the mid range, has anyone else had this problem? I am debating whether or not to keep that cam in there.

[grayracer513]

You may have the cam (or both cams) too far advanced. That would account for both your complaints I'd suggest double checking the timing.

[dirttrack25]

When i timed it i set the intake cam where i thought it should be and had the engine at TDC lining up the I. If the chain is overstretched could this be advancing the timing?

[essex426]

I just recently did the 450 cam mod to my 01 426. Today was the first day i have actually got to test it, and my results were different from others. I found that it actually wasnt THAT easy to kick and ALOT of top end power was lost, bottom was still OK but it wasnt all there and the power soon fades in the mid range, has anyone else had this problem? I am debating whether or not to keep that cam in there.

Look for a post called "got my 450 cam".Its 1 or 2 pages further on.Its got a usefull picture. That might help.And dont forget to count the pins on the cam chain.

[dirttrack25]

That was my post. I know its timed right from the way it looks but i dont know if the cam chain being overstretched affects it

[grayracer513]

An overlength timing chain will retard the timing. Remember when timing the intake that you need to have the front run of chain tight, and that means the exhaust cam has to be in place.

[dirttrack25]

Well I retimed it today and I'm pretty sure its correct. I only had a short ride as I had to go to work. Im going to give it another chance, but if I dont like it and have to go in to mess with timing again, the stocker is going back in. Am I the first who hasnt like this mod? Everyone else seems pleased...

[Raven1911]

How can you tell if your timing chain is stretched? Is it just safe to replace it when you do the exhaust cam??

[MNellis]

Well I retimed it today and I'm pretty sure its correct. I only had a short ride as I had to go to work. Im going to give it another chance, but if I dont like it and have to go in to mess with timing again, the stocker is going back in. Am I the first who hasnt like this mod? Everyone else seems pleased...

If you decide to get rid of it, let me be the first on the list to buy it from you. I'm serous. I just ruined mine when a valve broke recently and I need it replaced.

[Matt96xr6]

To check the chain, you need to reference the manual. Usually they have like a 20 link length to measure.

If the timing is correct, my next guess is that you are to rich on your jetting. The different cam may just be bringing that to light for you. The 426s are not known for good jetting from the factory.

[odlaw19]

The Yamaha manual doesn't have a "limit" listed.

[DigilubeJay]

A new timing chain should be mounted any time you have the cam caps off for any reason. Chains are mucho cheap.

Did you set the valve lash when you placed the cam in, or simply put it in an button her up?

If you got a cam from HotCams, you will most definately need to make a valve shim change right off the bat.

Most folks who have this problem simply have the cams rotated wrong. I'd triple check if I were you.

When I see that you say it doesn't kick over that easy, I am even more inclined to think you have them out of timing.

You can reach down and start a thumper with your hand after a successful cam change if things are right.

[ovrrdrive]

You can reach down and start a thumper with your hand after a successful cam change if things are right.

Well... I could start mine with my hand if I had to prove a point, but repeated hand cranking would result in a very big bicep.

It should be easier to start, but not so easy that foot cranking is optional.

Correct me if I'm wrong, but it should be the same effort as the 426 with the manual decomp pulled right?

As for the original post, I don't know how much it means, but my first impression was that the timing was retarded.

Strong bottom, weak top, still starts...

[grayracer513]

Correct me if I'm wrong, but it should be the same effort as the 426 with the manual decomp pulled right?

As for the original post, I don't know how much it means, but my first impression was that the timing was retarded.

The reason I suspect the cam of being advanced is because he's complaining of lack of top end, and if you remember from the days when the WR guys would re-time their cams to YZ spec, they retarded the exhaust cam to do so. Also, if the cam is advanced, so is the timing of the decompression pin, and the high cranking effort could well be due to the exhaust valve seating too early in the compression stroke.

The cranking effort should be quite a bit higher than a 426 with the manual release pulled because in the manual setup, you release all compression for the whole stroke. In the auto decomp system, the left exhaust valve is lifted off its seat as the compression stroke begins, but reseated again before the stroke ends. What would have been nearly 200 pounds of cranking compression is reduced to about 120 that way by effectively shortening the compression stroke. This was primarily done to accommodate e-starters, but the kickers benefited from it too. I can tell you that even with this feature, no one short of a defensive end is going to crank my 450 off by hand any time soon. The rings seal too well.

On the timing chain, unless you can spot some damage to it, find any tight links, or see that it has a lot of clearance and is loose at the pins when you push and pull on them, the only way you can really tell is to lay your old one next to a new, or look up the pitch somewhere and measure it. The manual gives you only the standard catalog number of the chain type used and the number of links. If it's been in there for more than a season or two, you're better off just to replace it for the less than $20 it will cost. It's about an extra 30 minutes work with the cams opened up.

[dirttrack25]

The timing may be off but, the feeling of the top end seems lean...I have added Thunder Alley exhaust but why not the change until now? And yes, I reshimmed the valves.

[DigilubeJay]

I mentioned the starting by hand, because adding the decomp cam does indeed make a dramatic difference in the force needed to crank it over. Right after I installed the cam on my 444, I had to prove my point a few times to others who also felt there was no way I could start the bike by hand. BTW..I am about 1/2 the size of a DE.

(I love doubting Thomas'...especially when I already know the resutls )

dirttrack25, one more thing to check is the cam chain tensioner. Make certain it is returning to the sping loaded point and keeping the chain taught.

[bigdrtrdr]

I just changed my 01 WR426 to an 03 YZ 450 auto exhaust cam.

Soffened the bottom hit a bit, a little torquier in the mid. and pulls hard all the way to the limiter.

The only thing I have noticed it the Auto Comp. Cam seems to make a little more noise the the stocker.

Its way easy to start, One kick and Im gone!

I should note that I had our dealer do the swap for me.

$149.00 plus tax including the cam! And a 90 day workmanship warranty to boot.

For that price it wasnt worth screwing around with at home.

[dirttrack25]

Heres another reason I think it may be lean. If you remember from my first post about this cam mod, my shim numbers were smaller than stock... all my info said I would need about .1 to .2mm thicker. I didnt check clearances with the stock cam, but since I had to get smaller shims instead of larger this would mean that from stock my EX. valves were too tight. When I reshimmed them this opened up the valves more, letting out more exhaust, which would cause lean condition correct? For the hard kicking...maybe im just a puss? Maybe it isnt timed right? Ive done the best I can do so if someone wants to lend a hand I live in Enfield IL

[FZ1426]

The reason I suspect the cam of being advanced is because he's complaining of lack of top end, and if you remember from the days when the WR guys would re-time their cams to YZ spec, they retarded the exhaust cam to do so. Also, if the cam is advanced, so is the timing of the decompression pin, and the high cranking effort could well be due to the exhaust valve seating too early in the compression stroke.

The cranking effort should be quite a bit higher than a 426 with the manual release pulled because in the manual setup, you release all compression for the whole stroke. In the auto decomp system, the left exhaust valve is lifted off its seat as the compression stroke begins, but reseated again before the stroke ends. What would have been nearly 200 pounds of cranking compression is reduced to about 120 that way by effectively shortening the compression stroke. This was primarily done to accommodate e-starters, but the kickers benefited from it too. I can tell you that even with this feature, no one short of a defensive end is going to crank my 450 off by hand any time soon. The rings seal too well.

On the timing chain, unless you can spot some damage to it, find any tight links, or see that it has a lot of clearance and is loose at the pins when you push and pull on them, the only way you can really tell is to lay your old one next to a new, or look up the pitch somewhere and measure it. The manual gives you only the standard catalog number of the chain type used and the number of links. If it's been in there for more than a season or two, you're better off just to replace it for the less than $20 it will cost. It's about an extra 30 minutes work with the cams opened up.

I concur. I got a lot of crap from guys on this site when I said mine was hard to kick after the mod. I'll take it that way thank you very much. Sorry I can't help you with your top end, mine runs great.(Hotcams).

[Fastest1]

The 450 cams base circle is smaller so larger shims are needed. The hit is different (not as abrupt) however I promise it isnt weaker. Starting is easy, real easy even bump starting. If any of the above is not true in your situation, something is set up wrong. I suspect valve clearances are way off if you had to go to smaller shims and look at the pictures of the cams installed screw the manual.