Handle Bars Moving?

I have had my TE250 for about 3 weeks now. I have had the handle bars come down on me 3 different times after landing jumps.

Fixes thus far:
1 - Tightened the handle bar clamps extremly tight.
2 - Took off the top clamps and bars and roughed up both surfaces with a round file to try and get more bite on the rougher surfaces.

Still came down again after this weekend. I am not jumping very high or far, may a couple feet at most for height.

If I put a shim in between the clamp and the bars (upper and lower) what suggestions for material?

Any other suggestions would be appreciated.

That seems really odd. Make sure that the clamps are not bottoming out on each other, and if they are, then shave a little off the underside of the upper clamp so that they contact only the bar when tightened, and not each other. This is the only suggestion I have.

That's about the only logical and practical suggestion there can be.

Buck32... if you need more than 14 or so ft lbs of torque to get a good clamp load on your bars, something is dimensionally or mechanically wrong.
As dfeckel suggests... other than something really odd, the clamps "bottoming out" before you get a full clamp load on the bars would be the most likely culprit.
Typically, properly torqued and "squared up" clamps will have about 1/16" to 1/8" gap front and rear.

C