Garden Master GMS 5 advice please

[Marb]

Hi all, I've recently got my first wood chipper a garden master GMS 5 it was'nt a runner when I got it but got the engine running in a few hours sharpened the blades and noticed the flywheel that the blades bolt to isn't flat and as every flywheel I have seen on Google images is flat I thought it was strange but looked factory so I tried to shred a pine branch approx 3cm thick tapering up to 3 inch thick, it made a lot of noise but not shredding,   

I'm convinced its not shredding because of the flywheel not being flat but I know next to nothing about these so advice would be good thankyou Mark.