YZ400/426 parts interchange

I have a few questions I hope some of you can help me out. Question#1. I am currently in the middle of converting my 99 YZ400 to a 426 internals. What parts do I need. I have been told that all I need is a 426 rod, wrist pin, and piston and cylinder. I was looking through catalogs and their are different part numbers for head gasket and base gaskets for the 400 and 426 If they interchange why are the part numbers different. Question#2 I started porting the head and was trying to figure out how smooth to make it. So far I have just smoothed out the casting marks with a 120 grit sandpaper roll on a die grinder. Several people have told me to leave it a little rough, and some people tell me to polish it as smooth as I can get it. Who do I listen to. Question#3 What kind of cam should I use. I have been told that Hot cams are junk. I installed a set of hot cams in a buddy of mines KFX400 quad and the installation went smooth and he was happy with the power increase. If they are junk what other cam options do I have. There the only manufacture that I have found that makes a set of cams for my bike. If any body has any input I would greatly appreciate it.

1. I don't know the bore of the 426 and 400 but if they are different, which is safe to assume since you need to replace the piston, then the inner diameter of the base and head gasket will be different between the two.

2. Typically when porting the exhaust port can be polished but the intake should have some texture to it.

3. Don't have any experience with hot cams but they seem to do good business, companies that are junk don't last long.

If you've been "told" by the same person the gaskets are the same, polishing the intake is good and hot cams are junk I'd stop listening.

use the 450 cams

i did that mod also...you need a 426 rod, gasket set (topend) .if you have ne questions pm me il get back at ya

Soo,, 400 bottom end - 426 head - 450 cams ( what years? ) does anyone have experience with the Luke's 420 kit? I'v got a 98' 400 ( rode hard, high hours) and a spare 99' bottom end with no head, can i use a GEN 1 450 complete cylinder head? or 426 complete head with 450 cams? what about the dowl pin issue?:thumbsup:

...can i use a GEN 1 450 complete cylinder head?
No. But if you rebuild your crank with a 426 rod, you can then use the complete top end from a 426 (it will then be a 426).

Look at the lower cam sprocket if it,s bad buy a new crank half or just a new 426 crank.

The small end of the rod is different from the 400-426?? I believe that the stroke is the same ( 60.1 ). Long rod short piston ?

Follow me on this: The 426 has a larger wrist pin, and a larger bore, but the 426 cylinder fits the 400 bottom end. You need the 426 rod so that you can run the 426 piston with the 426 cylinder and end up with a 426. In fact, you can use a 444cc big bore kit for a 426 on your engine by using the 426 rod. Be sure your clutch is healthy.

Does anyone know if a 426 head will fit a 400 cylinder? Can you resleeve a 400 cylinder to 95mm?

Does anyone know if a 426 head will fit a 400 cylinder?

AFAIK it should fit.

Can you resleeve a 400 cylinder to 95mm?

Even if it's possible, I don't think it's worth it. I'd better buy a 426 jug and sell the 400.

426 head will fit a 400 cylinder, but it doesn't have the remote hot start nipple for the really old FCR carb. There's a boss that you would have to drill out and press in a nipple.

If you are going to use a 426 complete crank (as opposed to just replacing the 400 rod with a 426 rod) you will need a new primary drive gear and new counterbalance drive gear as well. The 400's were keyed to the crank with a square key. 426's are splined. Not sure of the retaining nut is the same, so you may want to order one as well, and the lock washer.

Use the 426 head gasket with 426 bore or you will hit the edge of the gasket with the piston. The rest of the gaskets are the same.

Luke's 444 kit kicks serious butt. Good product at a great price. If you go 444, you will need a Cometic or Wiseco head gasket to match the bigger bore. I've had better luck with Wiseco than Cometic, but to each his own.

Hot cams are not junk. Lots and lots of miles on mine. If you are just using the exhaust cam to get auto decomp, use either hot cams or OEM 03 YZ450F...grind is about the same. If you are doing both cams, then go for the hot cams as the intake gives a considerable boost in mid range and above without a big sacrifice on the bottom.

Web Cams also have a very good rep, but I have never used them...

Good info and tips, i'm going to see what i can make up. Awesome


I'm planing on runing the Luke's 444 kit, do i need to run a 450 carb? Do i need to upgrade the cooling system for CA desert conditions? How late 450 cams can i run in the 426 head?

Yes! iam the Question man

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