1998 wr400f failures

I have approximatley 5000 miles of aggressive tight trail riding on my 400. Only trouble I've had (besides normal wear and tear)is a cracked throttle valve, (Just the flat part) which caused a very high idle. It must have been a defect. I'm now hearing some knocking or slapping noise inside the motor. I will rebuild the engine this winter....Rings, piston, timing chain, and check the rod etc.. Is there anything else that has given big troubles that I need to be aware of that should also be replaced while I have it down? Maybe the water pump or\and the oil pump? Also is there any place more reasonable on prices? I paid 70 plus dollars for that throttle valve that had about .03 cents worth of material in it, about the size of a half dollar.



the sound of your little end going is that of a little knocking noise every time you rev the engine through mid revs. "the little man with the hammer"

this can be heard just as well while revving at standstill.

if you pull the top end down get the LE measured with an internal micrometer and check the spec on it.

if in doubt have it out.


Thanks for the reply Taffy. I learned the hard way once before. I will check that for sure.



My high mileage 98 WR needed cam chain and guides replaced at the 6000 mile mark. The motor was making noise at idle from the chain slapping the worn out guides.

The piston and rings were in tolerance but got changed anyway. I agree with Taffy's comments about the piston pin bearing. I have heard the same information from other reliable sources.

The water pump seal and impeller shaft are other must check items during a rebuild. I have seen several 98`s with coolant dripping out of the pump weep hole.

I have never heard of an oil pump failure on these machines or seen a posting on TT about one.

Zaknavage, yesterday while changing the oil on my 98 I noticed some residue around the weep hole on the waterpump. What should I change to make sure everything keeps working properly. I am going to buy a 2000 waterpump impellar because I have heard they work better and cooling has always been a problem for me. Thanks, Eric

Hey BB,

I have to admit ignorance. My 98 has never sprung a leak at the weep hole. I have never been inside the water pump.

The update on the impeller is a good idea. The part number for the impeller changed after 98. I can't say if your cooling will be better with it or not.

My 2000 wr400f's conrod snapped cleanly about halfway up the rod. The broken rod punchecd a hole through the casing at the front of the engine and through the back of the cylinder wrecking the casing and the cylinder. the conrod also smashed the balancer, wrecked the piston. about the only thing the conrod never came into contact with was the gears. i only had this bike for a week. i bought it second hand. i ended up selling the bike for parts as it had a vortex ignition, white brothers exhaust system, tuned suspension, two sets of plastics, the standard ignition, all the standard road gear, standard pipe and also a set of triple clamps to fit oversize bars. over here in australia they brought out a 2005 xr400r which is jut the us 2004 xr400r with some different graphics. wr400f just go over everything when you take the engine apart. check the rod for cracks, crankshaft for wear and play. if everything is fine you should have one awesome bike when it is rebuilt.

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