Yet another top end rebuild question, Vibration

[Kwakasaki]

Just replaced the piston on my 04 KDX220. Had the cylinder honed and just cleaned the head up as it was in very good shape. Used a stock Wiseco piston and ring set and replaced the rod bearing. Probobly went a little over board but went as far as to check ring gap and skirt clearance and it is within the tolerances allowed in the Kawasaki manual. Fired it up and went thru three heat cycles. Rode it thru the gears slowly up and down the street, let it cool down and did the same two more times. I am running heavy on the premix for breakin. Next time down the road I went about 1/3 throttle and went thru the gears clearing it out. I did this four or five times and it felt strong. What I did notice is alot more vibration. It diffenently is assemlbly vibration. :bang: To be safe I grabbed another head gasket and pulled the jug to make sure a clip had not backed out and the pin was walking back and forth. The pin, rings, piston looked perfect. I put it all back together this afternoon and took off. Same thing. Im sure there is a weight difference from the stock to the wiseco and I am feeling a difference in the balance of the rotating assembly. I didnt go as far as to weigh the pistons but i am assuming this is what is happening. Has anyone else run into this? :ride:

 

[Kwakasaki]

Must have got to technical on the first posting, lets try this a different way. Has anyone had a noticable difference in vibration after chaging the stick piston on a kdx220.

 

[Red_Chili]

I recently renewed my top end on the 220, new to me, few hours, stock piston, noticeable piston slap, and used a Wiseco piston/pin/bearing, and all I noticed was the lack of piston slap and maybe a tad more power!

 

[TriniG]

Check exhaust

Sometimes if the Pipe is not tightened down properly, you get terrible vibrating noises. Check the Pipe mounts and that the header springs are properly installed.

 

[Rhodester]

The first thing that came to my mind was the fact that you said that you were running heavy on the premix oil. To me that means that you have leaned out your fuel to air ratio and could be running lean. Add to that the possibility that you may have not have richened your jetting for cold weather riding. Both of these issues could lead to seizure damage. Could that be the problem? What is your temperature? What is your jetting? What oil ratio are you running in relation to what you WERE running?

 

[Kwakasaki]

I took most of that into consdieration before i tore it back down. Going to ride this weekend and keep an eye on it. Im pretty sure its a recepricating weight issue, thanks for the excellent info.

 

[ridejunky]

Although your explanation of the vibration is descriptive, it is still difficult to quantify (Is it alot, are the
handle bars shaking?) Many people have done piston changes including myself, however this is the first time I have heard of it causing vibration. I would check to see if your crankshaft runout is within
tolerances. If the flywheels are in either horizontal or vertical misalignment it will cause vibration.
It is possible to cause vertical misalignment if too much force is applied when trying to remove or install the piston pin. Any way, I hope you can find the source, let us know how your ride went!

 

[Kwakasaki]

Very good points. It went with ease so i dont think i would have effected any tolerances. I cant rule out my 12 year old didnt take a hammer to it when i wasnt looking : ).
I went to ride a few laps today and all went very well. The third time I took it out i rode it like i stole it, and she screams. No bottom end noise and the top end is so much quieter than before the top end change. The vibration is not near as bad now. Only off idle to mid throttle just like during break end. Felt too good to do anything now, but if you hear a big KaaaaBaang this weekend something went wrong LOL.