(Well this doesn't work on rotator)
1. Select your piston
2. Go to the XML editor
3. Click the input controller
4. Change from VTOL to this, Activate2 + 0.1 + Throttle
5. Set the piston speed to 9[900]
6. Click the piston editor [it should be a gear icon]
7. Set the activation group to 1
8. Make the engine block
9. Make the oil pan
10. Make the engine head
11. Make the head cover
12. Make the gearbox & starter
13. Make the oil filter

Then it should be completed
How to start?
Simply Activate 1 and then 2