your work with slight modificationsExceptional! What you want to do is to make a block (or small cylinder) and then the piston and the motor which you will each attach to it (alternatively the motor could be attached to the rotor). then group the three (the block and the two joints). Then attach the piston to the vehicle and the motor to the rotor. I have also found that when attaching multiple joints to the small block, it is useful to keep them on different layers. (SP puts them on a dedicated layer but you can change that). I'll try and work up a small tutorial using your model later today (nothing like SP on Father's Day) but try doing it on my cryptic instructions...you might get more out of it. Finally make sure to then set the grouped block to nocollision. Again...excellent work.
...Looking again at your model I might propose this. Group the motor with the rotor...(first attach and then group).
Then make the whole main body of the vehicle a group. Next attach each motor/rotor to the overall vehicle group.
You should now be able to pick up and throw the vehicle around with the rotor's attached and spinning.
Depending on what level you are in school or sketchup....the next steps could either be simple...(attaching the vehicle group to a piston) or else using ruby sphysics push statements or a thruster value and gyron on the main body to fly around.