Why the engine shake

Hello. For the first time I try to use Blender 2.6.2 Cycle to animate/rotate my engine. (Not ready yet)
I put the engine, cylinder at center. With shiftbutton down I select the cylinder-text-camera and then the curve and follow path frame 1-250 and press Alt+A
Engine rotate, yes, but shaking. Why
Do you know why let me know
Thanks in advance
Karl
By the way. Can I render with H264xAVI+Anim to get a video as I always do in Blender Internal.

http://www.pasteall.org/blend/12424

Increase the resolution of the curve, doubling it to 24 smooths it out, but you might want to increase it to 36 just to be sure it will be extra smooth when rendering…

Randy

Thank you. I increase the reolution to 36 and press smoth and my engine rotate smoth
Perfect
Karl