98 yz400f engine noise

Has anyone had a problem with an engine noise that is hard to diagnose. It sounds like piston slap that gets louder as motor revs up. To date I have done the following with no success: -Changed piston rod, new piston/pin/circlips, checked measurement of the cylinder, new cam chain and adjuster,checked valve clearence, visual check of all bearings, gears and clutch assembly. I have not replace any bearings because they all felt ok when I inspected them. I am totaLLY STUMPED. :)

Freestyle111,thanks for your thought. I will check out the archives, but I bought this bike brand new, and this noise is way to loud to be normal.

I'm stabbing in the dark here, but have you checked the key on the counter balancer to make sure that it's tight? Some of the earlier models had a problem where the key would loosen over time and the loose counter balancer would cause a loud noise. I have not dealt with this personally but I've read about it on this message board. Maybe the search will turn up something useful with more details. I hope this helps.

if you search archives you will find a ton of post regarding 98wr400 engine noise.you can stop wasting your $ the noise is normal.

Yep, I am going to try looking at that as soon as I get this darn cast off my arm. ( that is a whole other story) I found the discussions about cb gear keys thanks to freestyle111's suggestion. Thanks for backing up the idea.

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