WR 400 Help!! Bad Vibration, getting Worst

hey i have a 1998 Wr 400 that i bought about a year ago, i just finished doing the top end about 4 months ago, just put in new intake valves, timing chain/tensioner, and new seals. the bikes only problem up until now is it would slip really badly in 5th but was fine in all other gears, and the engine ran really smooth and had lots of power. but i been doing lots of riding lately and have noticed its developing a really bad vibration, that runs progressively through out the rpms, the only changes ive made recently, is i started runnning semisynthetic oil in it (10w 30) in it. i would really like some imput before i go head strong into tearing the engine down thanks...j16out


Did you ever come up with anything on your vibration, I have an 08' that appears to be doing the same thing?

hey there, to be honest i never came to any conclusion, it probably quite possibly was all in my head, but i would check all the common things, check all your frame mounts, make sure their tight, check your clutch basket assembly making sure the main nut didn't break loose, you can check to see if theres any play on your main bearings, check your connecting rod for up and down play on the big and small end if you get down that far, i ended up tearing the motor right down, did a complette rebuild from transmission up, mine did have tranny probs, but that didn't seem to solve the problem, after a full rebuild it still has a bit of vibration ive just come to except it. my yz 250 vibrates a little because the clutch basket has a little play in it, been like that from day 1 haven't had any problems yet, hope this helps best of luck!:busted:

Well I found out what was causing the vibration. The woodruff key on the counter balance sheared off causing the weight to rotate and thus causing said vibration. The mateing surfaces for both the shaft and the weight were marred up a bit, I check on getting a new weight and it has to come from Japan on a boat...about 6 weeks to get it.

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