Re: very new to this motorbike thing with a few questions
And, in spite of what you might have been told, DO NOT START TAKING YOUR ENGINE APART.
This is bad advice for a new builder with little to no experience with these engines. The odds are in your favor that the crankcase doesn't have trash in it.
As for checking the displacement, it's almost certain that you have either a 49 or a 66/70CC engine. They only come in two sizes. You might see ads for an 80cc engine but that is measured by including the combustion chamber volume. There really are no 80cc Chinese bicycle engines out there. My guess is it's a 66/70cc. They seem to be the most common but even if it's the smaller version there's not that much difference in power output. To confirm you'd have to measure your bore and stroke.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"