Little education here and do not feel bad as we all had to learn. All engines are very similar on how they are made and put together. The top two are Zenoah #1 many use Zen and falling close behind is Chung Yang most just call them CY. There are some others on the market like HY but the Zen and CY are the top two. Most parts will swap one to the other. The name should be on the engine on the bottom of the cylinder on the clutch (power take off side}. Many times it is on the pull starter and some Zen have it on the plastic cooling shroud near the spark plug. Like I said most parts are interchangeable so it could be a mix of both if someone has messed with it.
Then you have basically two major categories 2 bolt most common as they have been out years longer then the 4 bolt that came out much more resonantly. This refers to how many bolts hold the cylinder on. Then there are different displacements most common stock motors 23,26,27 and 29cc. All of them are rounded up to the next highest CC. Like the 29 is really 28.5cc but rounded up to the next highest cc called a 29.
Now the standard modified engines that go up to 30.5cc but we will not get in to that just now. There are bigger engines but are not what I call a standard engines and take mounting kits special pipes, modifications to install and so on.
Zen are fairly hard to tell what size with out taking apart but on a CY be hind the fly wheel on the bottom of the cylinder will have something like 28-34 which means it has a 28mm stroke with a 34mm bore which makes it a 26cc which in reality 25.4cc but like I said they round it up to 26cc. If the engine has been modified the stroke part could be wrong but the bore will stay the same. This will give an idea on most stock engines. Maybe others can add something.
