yz400f '98' help please


9 replies to this topic
  • yamaha mark

Posted August 23, 2009 - 02:17 AM

#1

hi to all,ima a newbie so be gentle with me.i have a 98 yz400f and its a great bike but i done some gnarley damage to the head and piston. a lifter exploded breaking a valve and the valve punched a hole through the top of my piston.as i need to get a new head because of the damage done to the underside of it the only readily avalible heads are off yz or wr 426's and 450's.can i bolt one of these heads on and ride away or is this going to be more trouble than it worth.any suggestions would be gratefull.
thanks.
mark.

  • Dee Perry

Posted August 23, 2009 - 03:06 PM

#2

Hi Mark, I do not have the answere, I did the same thing to my 426 2 years ago, I do not have the knowledge so it went to the dealer. However I have seen numerous posts on your exact question. Do a search on your keywords and you will find lots of info. Goodluck

Dee

  • yamaha mark

Posted August 24, 2009 - 12:05 AM

#3

thanks dee

  • pablo83

Posted August 24, 2009 - 06:56 PM

#4

hi to all,ima a newbie so be gentle with me.i have a 98 yz400f and its a great bike but i done some gnarley damage to the head and piston. a lifter exploded breaking a valve and the valve punched a hole through the top of my piston.as i need to get a new head because of the damage done to the underside of it the only readily avalible heads are off yz or wr 426's and 450's.can i bolt one of these heads on and ride away or is this going to be more trouble than it worth.any suggestions would be gratefull.
thanks.
mark.


Any YZ or WR 400 or 426 head WILL fit no problem. The heads are all identicle, but the 400's came with steel valves and the 426 had titanium.

I do not think the 450 head fits, but I could be wrong.

  • bakeyz426f

Posted August 24, 2009 - 07:52 PM

#5

the 2000 model 426 had stainless steel valves. they can be used in any of the 426 heads as well.

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  • pablo83

Posted August 24, 2009 - 09:13 PM

#6

the 2000 model 426 had stainless steel valves. they can be used in any of the 426 heads as well.


Was that for the WR or the YZ or both?

  • bakeyz426f

Posted August 25, 2009 - 03:32 AM

#7

i think both

  • pablo83

Posted August 25, 2009 - 07:49 AM

#8

i think both


You're probably right. Now that I think about it, in 2000 the WR was still a 400 (but the YZ was up to 426) so the WR definitly had steel valves that year.

  • Birdy426

Posted August 26, 2009 - 10:24 PM

#9

Yes, both. YZ cam timing was different, but you can YZ time a WR or WR time a YZ...no big deal. The 2000 YZs had SS valves, too.

The only difference between the 400 and 426 heads (other than valve material, springs, keepers etc) is the vacuum port for the hot start octopus on the 400s. There's a nipple on the L/H side of the 400 head in the intake tract to provide vacuum for the hot start. On the 426's with the second generation FCR, the hot start is part of the carb, so the nipple is not fit to the head...there's just an undrilled boss there. To use a 426 head on a 400, you must drill out the boss and press or thread in a nipple. To use a 400 head on a 426 (as I have), you must cap off the nipple (or remove it and plug the hole)

  • yamaha mark

Posted August 27, 2009 - 12:03 AM

#10

thanks to everyone for your help




 
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