400 to 426 conversion, the easy way



48 replies to this topic
  • toyotanick

Posted January 26, 2012 - 07:52 PM

#21

ok thanks for the guidance. would you happen to know if a wr 5th gear is taller than the yz400's? i think i said this already but this bike is a supermotard and a taller 5th would help quite a bit.

  • grayracer513

Posted January 27, 2012 - 08:02 AM

#22

Yes it is taller. There are several threads on that subject. The whole WR gear set would give you a lower low and the higher 5th, but an alternative approach is to us the WR 4th and 5th. You end up with a first four just about exactly like the early YZ450 4 speed, plus the higher 5th on top.

  • toyotanick

Posted January 27, 2012 - 09:39 PM

#23

i searched wr 5th gear and other forms of that but nothing shows up that is useful. what do i need to search? and how the hell do i find those gears? can't find them on ebay and do not want to buy them from yamaha.

  • grayracer513

Posted January 27, 2012 - 10:55 PM

#24

Other than what you've already read, what do you need to know?

As far as finding them, there were always fewer WR models made and sold than YZ models, so even though you have 1998-2002 models to pick from, there's only a few out there, and only a small fraction being parted out. I'm afraid that if you want them right away, you're going to have to bite the bullet.

  • toyotanick

Posted January 29, 2012 - 07:28 PM

#25

since you seem to know quite a bit about these bikes, i am wanting to do a high wattage stator on my 98 yz400f and can't find one that is said to be worth buying. i have put a yz400f stator on a 04 yz450 and the bike have been running for at least a year. I'm pretty sure that they make more yz450 high wattage stators so could i do a 450 stator on my 400?

i am already thinking about changing the 400 flywheel to a 450 because of the massive flywheel weight that is on the factory 400 flywheel.

  • umu24013

Posted January 29, 2012 - 08:02 PM

#26

since you seem to know quite a bit about these bikes, i am wanting to do a high wattage stator on my 98 yz400f and can't find one that is said to be worth buying. i have put a yz400f stator on a 04 yz450 and the bike have been running for at least a year. I'm pretty sure that they make more yz450 high wattage stators so could i do a 450 stator on my 400?

i am already thinking about changing the 400 flywheel to a 450 because of the massive flywheel weight that is on the factory 400 flywheel.


read this http://www.thumperta...9-which-stator/

  • crf-500

Posted February 02, 2012 - 03:06 AM

#27

their is a mildly chewed wr trany on ebay right now 90.00 .i,d only go for perfect gears but maybe the gears your after are in good shape

  • SB2

Posted February 02, 2012 - 08:25 PM

#28

For those interesed, the 450 piston in a 426 cylinder on a 400 rod sits .040" lower in the cylinder when measuring from the top of the cylinder to the top of the piston.

  • grayracer513

Posted February 02, 2012 - 09:19 PM

#29

Useful. Thanks...

  • umu24013

Posted February 03, 2012 - 02:03 AM

#30

For those interesed, the 450 piston in a 426 cylinder on a 400 rod sits .040" lower in the cylinder when measuring from the top of the cylinder to the top of the piston.

Did you measure this with a new base gasket? And what's the part number on the piston, 5TA / 5TJ / 2S2?

Edited by umu24013, February 03, 2012 - 03:28 AM.


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  • SB2

Posted February 03, 2012 - 06:37 PM

#31

Yes, new base gasket but I realized that I had a moment last night when typing that. It is .020" lower, not .040". Sorry guys.

  • SB2

Posted February 03, 2012 - 07:17 PM

#32

And the piston was from a 2007 which looks like a 2S2 part number.

  • umu24013

Posted February 03, 2012 - 09:19 PM

#33

Thanks for the input, SB2.

  • umu24013

Posted February 03, 2012 - 09:24 PM

#34

I think It would be interesting to find out the compression height of the above 450 pistons :smirk:

  • SB2

Posted February 04, 2012 - 07:24 AM

#35

I think It would be interesting to find out the compression height of the above 450 pistons :smirk:


I think I know what you are asking. Just give me a day or 2 to get if for you. I still have a 400 that I decided to keep and do the 426 cylinder, rod, and piston upgrade. But after reading the previous posts, I got curious. Before I got real deep, I had to stick in the old piston from my 450 to see how it really compared before I split the cases. I will start getting into my "project" a little deeper tomorrow.

  • SB2

Posted February 19, 2012 - 01:40 PM

#36

After a much more accurate measuring between the 400 cylinder/piston and the 426 cylinder/450piston, .030 was machined off the bottom of the 426 cylinder to get the squish back to where it needed to be. Motor is back together and almost in the frame.

  • Laurentian

Posted February 26, 2012 - 02:36 PM

#37

Good info !
I have a Wiseco 420 kit on a stock 400 rod.
Bike is very rev happy and super easy to ride.
However the 450 piston would be a good mod if ever the
420 piston / rings are no longer available.
I guess the key is to machine off
the back of the jug to get the stock squish back.
Can the cam chain tensioner take up the slack ?
Also I always thought most guys went with the 426 set
up to get the 19mm piston pin. I have had zero problems with
the 18mm but was under the impression that it
was the weak link ?

  • umu24013

Posted February 27, 2012 - 10:04 AM

#38

I guess the key is to machine off
the back of the jug to get the stock squish back.
Can the cam chain tensioner take up the slack ?

I hope it will... Otoh, this will retard the cam timing a bit.

Also I always thought most guys went with the 426 set
up to get the 19mm piston pin. I have had zero problems with
the 18mm but was under the impression that it
was the weak link ?

That's a good question

  • potman1980

Posted April 13, 2012 - 01:44 PM

#39

i'm considering doing this conversion myself now my 400 engine has just done its big end :thumbsup: i need to have the cylinder bored now and was wondering if its possable to bore the 400 cylinder out to the same size as the 426, or do you have to buy a 426 cylinder? does anyone know the ID of the 426 cylinder.

also is the 426 conrod the same length as the 400? just wondering if it would be easier for me to use a 426 rod on my 400 crank then bore out to426 cylinder and use th 426 piston. i need to change the rod anyway and wonder if it might be more reliable. :thumbsup:

  • umu24013

Posted April 16, 2012 - 09:34 AM

#40

does anyone know the ID of the 426 cylinder.

95mm

also is the 426 conrod the same length as the 400?

I'm pretty sure they are the same length (center to center)





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