Hydraulic cylinder help

Under the option Constrain use Type Mate and join two surfaces facing each other (inner bottom of cylinder and piston head) then use options under slide bar called Limits and type the limit dimensions. Minimum is zero position ( when the piston is set completely inside of cylinder) and maximum is a stroke of the piston.

Answered with a tutorial: https://grabcad.com/tutorials/hydraulic-cylinder-help--1

Look up inventor drive constraint in google this might be quicker.
http://www.youtube.com/watch?v=zRqOYADeObo

See if your part is flexible and not restrained by any Constraints or if your "Contact" is on or off

I don't know how to check that, I have briefly used auto desk inventor, I struggle with the simulation of the assemblies, I don't know how to move the piston forward and back within the case, shall i upload the assembly so you can take a look?

yes upload the assembly and i will take a look dont forget to upload the part files as well or it will not work.
ps what inventor are you using ?

I am using autodesk inventor professional 2015, its student edition

Ok heres a quick one so that you can see how it works

Ok heres using yours make all parts contact set. Ground your base part.Activate Contact Solver

Small tip try to keep your number of parts to minimum ie you could made this in 2 parts.

thank you for that, i will try it, it was my first time making a hydraulic cylinder

iv done all that, could you tell me how to simulate the movement of the piston?

later