Voice your opinion on the 2001 yz426f

Hey Im buying a 2001 yz426f and tearing down the motor (from the bottom up) I need suggestions on performance anyone recommend certain types of valves? or any other type of internal part before I start tearing this bad mamma jamma down? Im doing a budget build but if I come accross something thats gonna make a huge difference why not go with the best? NO SUGGESTION WILL GO UNCONSIDERED


Hows the clutch? Maybe new clutch plates or even the whole thing? Hinson makes good quality (ie: expensive) plates and a trick billet basket and hub. That would be a hefty chunk of your budget for the whole shabang but if ypur clutch just needs a little tlc maybe new plates.

Also i hear rumors of the auto decomp cam of the 450's fitting into thier ancestors the 426's never tried it so i don't know but my blue monster has auto decomp being an 04 and my buddies say its more user friendly. That would be worth your money exponentially after all most of us are in this sport for recreation so any thing that helps you have fun is a good thing right?:applause:

Use stainless valves not Ti, they last longer. Install the auto decomp mod if you want, my 01 426 is has the compression release and it's just second nature to me so I don't notice it. I really wouldn't try to hop it up to much. Maybe throw in a set of HotCams if you'd like. Most people will agree that a stock 426 with good jetting will yank your arms out of their sockets if you crack the throttle to hard. I know mine is stock and she's a screamer.

Use stainless valves not Ti, they last longer. Install the auto decomp mod if you want, my 01 426 is has the compression release and it's just second nature to me so I don't notice it.
You do have the option of using SS valves from a 2000 model (be sure to use the '00 springs, too!), but whether they last longer is questionable. I have an '03 with the original valves in it.

People who say the auto decompression cam isn't a big deal typically have never spent any time with one. There are a number of advantages, and no real disadvantages. I've ridden big singles since the British stuff in the '60's, and I am intimately familiar with compression releases, and what you can do with them. After owning auto decomp, I don't see why anyone would miss the manual release. Frankly, it's the best mod you can do to a 400/426.

Frankly, it's the best mod you can do to a 400/426.

Amen to that. Not just for ease of starting either, it also allows you to bump start the bike if you happen to brake stall coming into a corner and it gives the bike a little more low/midrange power.

My 426 is easier to kick over than my 250 2T's

If your going to do auto decomprission mod use the hot cams and I would use the Ti valves but that just me and oem piston I heard bad things from wesico pistons.

I rebuilt my '01 YZ426 over the winter; I put in the Hot Cams and a JE 13.5:1 piston and I love it. I did them both at the same time so I can't say for sure how much each did, but together they added power everywhere, especially on the bottom it seems.

To those who say they don't notice the routine for using the decompression lever, you notice it once you have the auto decompression. It's so much easier, I don't even have to worry about getting it near TDC, just give it a decent kick and it almost always starts first time.

Those are the two things I did when I was going to have the motor apart, a lot of the other stuff you can do without major surgery to the engine, so you can add them after if you want. The valves I can't say much about, I don't know anything special about them.

i have an 02 426 and have no problems what so ever with the manual de comp lever once u get a hang of it you get it to start up first kick every time everybody has there own trick and you can still bump start fine with the lever i do it all the time and never have to find tdc when i start it

My 2 cents on the Stainless vs. Titanium valves. The reality is, Titanium is lighter (less valve float in high revs) and will resist heat better then steel (less likely to warp or bend). Depending on which grade of steel these valves are made of, it may be harder as well. Obviously Yamaha used titanium for a reason, and thought it was beneficial, since its much more costly the steel. I doubt they just threw them in so they could brag about Titanium valves.

It's unlikely you'll ever see the advantage or disadvantage on a properly maintenanced, well running motor. But in times of over heating and rev abuse, the Titanium valves are a safer bet.

I'm a metallurgical engineer, so I have some good experience with these materials.

Just some things to think about.

There is no doubt of the superiority of titanium over stainless steel, but it does have a shortcoming as used for 4 cycle engine valves, aside from its very high cost. That is that Ti is not hard enough to resist wear at the valve face, and cannot itself be processed to be hard enough without loosing it's ductility and becoming unacceptably brittle. Yamaha's Ti valves are, therefore, coated with a form of titanium nitride that is harder that almost anything, and that works extremely well, as we all know.

But the coating eventually wears through, and the valves abruptly become unusable, generally without any prior warning, and must be replaced at once, before real trouble develops. Stainless valves are also hard coated these days so that the valve need not be hardened to such an extreme extent, but the base material is still much harder than Ti, so the wear does not accelerate as much once the coating finally fails.

From a practical standpoint, there are STILL YZ400's and 2000 model 426's running around in the world with their OEM SS valves in the head, many of them having never been adjusted. Given that, and the fact that Yamaha OEM SS valves cost 20-30% of what the Ti stuff does, I would use them in my own rebuild without even giving it a second thought.

For a 450, I would use the OEM Ti, simply because the available aftermarket SS products are no less expensive, and no more durable.

The exception to that MIGHT be the SS valve kits from Faction MX. These are priced attractively, and if feedback shows them to be reliable, they will be a good alternative for most people.

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