WR400 nightmare motor

8 replies to this topic
  • creepy

Posted July 14, 2005 - 09:15 AM


I got a 99 WR400F from a guy out of state, it had some knocking in the head that I thought was simple piston slap so I bought it for 1800. I tear into the motor and find the crank was bad. Got another crank for 278. Then I find out from a shop tech that the pockets in the head are worn out well past tolerance due to sand being in the motor at some point in time. So now the head is toast too. The only good things are the bottom end minus the crank (unless I hear from them even more stuff is toast, ugh) and the cylinder and piston.
Yamaha wants around 700$ for a complete cylinder head. Not cheap, but not bad considering what my KLX parts cost me.
What causes sand to get sucked into these bikes so I can avoid this happening under my ownership? Should I look into another motor?
The oil tank in the frame was all full of black goop also, and several rinses with solvent and compressed air havent cleared it. Anyone have ideas on how to clean this thing out?

  • sharpmarble

Posted July 14, 2005 - 11:23 AM


Go to www.crotchrocket.com they have that head for about $450 :applause: As for sucking crap into the motor, make sure the breather tube is either routed to the airbox, or put in a T and route another hose higher. If these bikes are stalled in water they can suck stuff up the breather hose when trying to restart it. It sounds like yours might have been fully submerged and probably not maintained very well :eek:

Good luck

  • rockieman

Posted July 14, 2005 - 05:57 PM


Sorry to hear your dilema it sounds like you got one abused bike. I've got 8000 miles on mine ('99) and outside of three valve adjustments has never had ANYTHING done to it. People talk about the XR motors and their reliability....I had a 600 of which I can't make the same statement. Treated right they are every bit as reliable with WAY better performance! :applause:
Good luck!

  • creepy

Posted July 15, 2005 - 07:07 AM


man, 8000mi. Not bad. Do you find you rev it a lot higher on the street? Im assuming youre using it on street to get that kind of mileage
that crotchrocket.com place had pretty good prices. with them I get 609$ complete for the head.
I guess Ill re-route that breather hose in behind the air filter so this doesnt happen again. ugh.

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  • jwriott

Posted July 15, 2005 - 07:09 AM


PM yzman400, I think he had somebody rebuild his head cheaper than that.

  • creepy

Posted July 15, 2005 - 07:26 AM


heh, thats not for the rebuild, its for the parts alone. The valve buckets on this head wore out the holes in the head so much even the oversized buckets wont work.
Im needing the head, valves, seals, springs, retainers, keepers and buckets

  • rockieman

Posted July 15, 2005 - 07:27 AM


[quote name='creepy']man, 8000mi. Not bad. Do you find you rev it a lot higher on the street? Im assuming youre using it on street to get that kind of mileage

Most of the miles are off-road....on road miles are only from connecting trails. I avereage 1200 miles a year....my bike is a '99 and I'm the original proud owner. :applause:

  • creepy

Posted July 15, 2005 - 07:35 AM


hmmm, thats a lot for trails. What I still kinda wonder is how these bikes hold up to extended period high-rpm loads. I dont see many street-going japanese singles with plated cyls.

  • creepy

Posted July 22, 2005 - 08:44 AM


629$ for a complete head and some piston rings. urgh.


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