100 psi would exert 829 pounds of force on a 3.25 inch piston. This would be more than sufficient to drive the piston to the bottom of its stroke. However, at the bottom of its intake stroke, the intake valve would still be open a bit and, at the bottom of the power stroke, the exhaust valve would be starting to open a bit.

It does appear that you would need to prevent the engine from rotating in some fashion.