WR 400 Bang Bang Bang....Oh no!!!

Ok guys,

I was out riding sunday and everything was going good. My buddy and I stopped for a few minutes and when I started the bike again I could hear a loud banging that sounded like it was in the top end. I quickly shut it down and proceeded to push my bike out of the deep ravine that I was in. After I got it home I turned the engine over with my hand while holding the compression release and could feel the engine just stop somewhere near TDC if I pushed really hard I could feel it break lose and make another rev. I'm thinkin a valve is hitting the piston. Has anyone had this happen to them? If so what was the problem and what all did it take to repair it?

The funny thing is my buddy's WR 400 did the same thing about 1 month ago. He has been putting off fixing it because he thought it was the lower rod bearing and wasn't thrilled about splitting the case.

Sounds like it could be a valve, but you won't know until you pull the head and see. You may be able to see a dropped valve just by pulling the cams and buckets, but I would go on and pull the head anyway, if you have a valve striking the piston then you will want to replace all of the defective parts. Hope you get it, and I hope you caught it quick enough not to cause much damage.


well because I heard my friend's bike do the same thing about 1 month ago the sound was familiar so it didn't bang many times before the engine was shut down.

I'm surprised that a single cylinder engine will even run with a dropped valve.??

Don't forget to check the Connecting rod small end bearing (piston wrist pin) while you are there.

Looks like you and your buddy are going to be hanging out in the shop together.

Good luck, Do a careful job.

pull it apart! post pictures!

anything found yet??

Haven't tore into it yet........Too many irons in the fire.

Hopefully I can start on it this evening.

Anyone know a good head work guy in the DFW area?

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