Please Help Wr 400 Motor Noise!!!

I have a 2000 wr 400 that made horrible motor noise. i changed the rings and checked the valves and everything in the top end is fine, i though i fixed the noise until i fired it up today and it was making a really bad knocking sound that seems like its coming from the bottom end. The bike runs great and doesnt lack power just sounds horrible, what could the problem be???

I have a 2000 wr 400 that made horrible motor noise. i changed the rings and checked the valves and everything in the top end is fine, i though i fixed the noise until i fired it up today and it was making a really bad knocking sound that seems like its coming from the bottom end. The bike runs great and doesnt lack power just sounds horrible, what could the problem be???

If it's a very steady metallic knocking sound, it may be the crankshaft. As the big or small end starts to wear, it knocks, sort of like a playing card in your bicycle spokes when you were a kid, only a bit more metallic. It won't affect the power until it gets really bad, but you shouldn't drive it anymore.

Did the connecting rod feel a bit loose when you were installing the piston rings?

I am just bolting my 450 back together after installing a new crank for the very same reason. The bottom end was knocking, and the big end bearing of the crank was gone. You can have your crank rebuilt.

There are 2 common issues with the 400f motor that can make a knocking noise.

If you are lucky it is just the counterbalancer key which is the most typical.

The gear on the end of the RT crank half has a key that locates the counterbalance drive gear. They often wear and even shear off. It is a easy fix. I think you can check it by removing the IGN cover and move the counterbalancer back and forth and and see if the gear has any play. You need to take off the whole rt side cover off the motor to fix it as the actual gear in n the rt side.

The second and more expensive issue is the small end bearing on the rod. You have to take off the Cyl and piston and see if the small end is worn at all. did you check it and the big end when you did the piston?

The 426 has a spined counterbalancer drive and a larger small end to correct these issues. Good luck.

ya i checked the small end and the big end they seemed to be fine i will check that key tommorow and let you know thank you for idea

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