Two Stroke Motocross Forum => General Two Stroke Talk => Topic started by: Sapper on March 19, 2012, 09:56:03 PM
Title: reduce vibration???
Post by: Sapper on March 19, 2012, 09:56:03 PM
I rebuilt the boys 05 KX250 and now more than ever it has a wicked vibration. I think it was like that last build but didn't really notice or care. It's not an out-of-balance issue. It's just the quick revving power of it. We have aftermarket trees w/ rubber bar mounts, Protaper fatbars etc. It's so bad that if sitting on the lift stand and have one hand on the rear fender and goose it, your hand slides down.
My son said the power is all there and screams. He didn't even get out of 3rd the whole day at practice. He said it gave him some pretty good arm pump but it's getting new steering head bearings one day this week when I find time.
Any ideas on reducing this?
Title: reduce vibration???
Post by: michwoodsrider on March 19, 2012, 10:28:09 PM
My first thought was a flywheel weight, but i read into it and it seems that doesn't help with vibration much just smooths the power out. Possibly worn crank bearings or an out of true crank?? I had really bad vibration on my RM-250 also i could clean the dirt off just by revving it on the stand But over all i think that's just the nature of a 250 2-stroke.
Title: reduce vibration???
Post by: factoryX on March 19, 2012, 10:30:07 PM
Idk, my yz250 isn't bad with vibration, and it isn't just the nature of 2 strokes. There is a reason why modern 4 strokes have counter balancers...
Title: reduce vibration???
Post by: michwoodsrider on March 19, 2012, 10:34:56 PM
Idk, my yz250 isn't bad with vibration, and it isn't just the nature of 2 strokes. There is a reason why modern 4 strokes have counter balancers...
Yea you're right there. I'm just saying 2-strokes vibrate a little more, because they don't have a counter balancer. Some more than others.
Title: reduce vibration???
Post by: cnrcpla on March 20, 2012, 12:19:28 AM
As long as your engine mounting bolts are tight, and all the other bolts are tight, then I wouldn't even worry about it. My YZ is pretty good as far as smooth running, but all two strokes vibrate a little. It's just something you learn to expect
Title: reduce vibration???
Post by: factoryX on March 20, 2012, 12:57:48 AM
Title: reduce vibration???
Post by: motoman356 on March 20, 2012, 01:14:34 AM
the vibration is due to a crank that isnt blueprinted. this is common in all bikes as the parts are specific to each bike so there are small imperfections and in 250ts its very noticeable. in a recent article in dirt rider Rick johnson rode a 250f and commented about his factory CR250 bike he said the factory 250 had so much power he had to tone it down to ride it and it had almost no vibration
Title: reduce vibration???
Post by: Sapper on March 20, 2012, 01:56:14 PM
After seeing that video, I guess it is the crank. I only use Hotrods, but I think next time, I'm gonna have Brent from TDC do one for me. No matter what the cost, I think it would be worth it.
I can't see trying to fit a custom counter-balance assembly on a bike though. Unless it were real small and not stick out.
Title: reduce vibration???
Post by: eprovenzano on March 20, 2012, 02:45:03 PM
One thing I've found to reduce vibs is to replace the exhaust springs. I had bad vibs with my 300. I started checking all the usuall suspects, motor mounts, etc., etc. I don't remember why, but I decided to check the header pipe. When I pulled the springs, they "seemed" fine, but since they're cheap I threw a new ones on... what a difference. The vibs didn't go away, (they never will) but were reduced. I have issues with my hands going numb, so I'm always looking for a way to reduce the vibs... without going to a stroker.
That reminds me, its been a few years, and I should replace them again...
Title: reduce vibration???
Post by: Charles Owens on March 20, 2012, 07:17:12 PM
7/8" bars are a little more forgiving with vibration and arm pump too.
Title: reduce vibration???
Post by: eprovenzano on March 20, 2012, 07:23:28 PM
Flex bars are pricey, but are supposed to help eliminate the vibs, and really help with arm pump
Title: reduce vibration???
Post by: twosmoke595 on March 20, 2012, 09:29:11 PM
also, what i've been using ebcause i get really bad arm pump, is the tag rebound grips, they look like they have little spikes on them, they make it to where i dont have to grip as hard on the bars, but they allow me control as well
Title: reduce vibration???
Post by: metal_miracle on March 20, 2012, 10:14:59 PM
i would check all motor bolts and headstay..
as for grips i have tried most of them. from pillow grip to soft pro taper..
but the best i have used is PRO GRIP 791
Title: reduce vibration???
Post by: dsrtrider48 on March 21, 2012, 03:29:34 AM
I remember old articles with team green and kx500's which used to vibrate.
they balanced the crank, blue printed engine, carefully bolted/welded everything, used a bar snake with weighted bar ends.
Title: reduce vibration???
Post by: SachsGS on March 21, 2012, 05:22:04 AM
One of my neighbours has an 05 KX250 and I don't recall it vibrating excessively.
But over all i think that's just the nature of a 250 2-stroke.
