2001 426 head

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#1
I was wondering if the '01 YZ 426 head would transfer over to my '99 YZ 400? If it does, what are the gains (if any)? Thanks.
 

Rich Rohrich

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#3
There is no performance difference to be gained by changing just the cylinder head.
 

Thump

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#5
The rod from the 426 is beefier. I think they can cange out? Rich is that corect?

Also the radiators are larger on the 426 but you would then need to run the 426 shrouds due to bolt position.
 

Rich Rohrich

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#6
Originally posted by Hot4Teacher
Would the 01' head increase reliability/durability?
Nope, sorry.


Thump is correct. The 426 has a connecting rod with a larger piston pin. It tends to hold up better than the earlier 400 rods, which were know to break near the small end without much notice.

You can rebuild the old 400 cranks with a 426 rod if you use a 95mm 426 piston & barrel or a suitable Wiseco piston for the 426. This is a very good mod for increased torque and as a bonus improves reliability. It's well worth the effort
 
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#8
Would the carb change over from the '01 426 to the '99 400? If it does I would think that a jetting change would be needed.
 

Rich Rohrich

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#9
The carb should work with only minor adjustments.
Most people end up using the 426 needle in the 400 carbs.
 
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#12
Originally posted by Rich Rohrich


You can rebuild the old 400 cranks with a 426 rod if you use a 95mm 426 piston & barrel or a suitable Wiseco piston for the 426.
I am wondering if I understand this correctly. Are you saying you don't need the 426 barrel if you use a wiseco piston?

Thanks for setting me straight
bake
 

Rich Rohrich

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#13
My choice of words was poor and made the whole thing far too confusing. :eek:

Wiseco only makes 92mm & 94mm pistons for the stock 400 rod.
If you go to the 426 rod you have to go to at least a 95 mm piston (either OEM or aftermarket). You can't bore and replate a YZF400 barrel to 95mm (94mm is the limit) so a 426 barrel is also required with the 426 rod.

I haven't found any piston company building pistons for the 426 rod smaller than 95mm.

The 94mm setup works really well in the old 400s but if you are going to run at high rpm you have to make sure you have a fresh rod in the bike because the 94mm piston is much heavier than stock and will stress the rod a lot harder. If you have to rebuild the crank anyway you might as well just buy a 426 rod and barrel and do it right. ;)
 

DPW

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#14
I'd swap the complete stock exhaust from the '01 YZ426F to your '99 YZ400F, assume the exhaust is stock on the '01 and in good shape.........