Mike,
You can pick up a comression gauge pretty cheaply at any auto supply store. Just make sure it has the same thread as your spark plug.
Take out all the spark plugs and install the gauge in one cylinder. Crank the engine with the mags off for a few seconds and note the PSI, then do the same in the other cylinder.
On a new engine the readings will be between 100-120 PSI. Anything above 80 PSI is acceptable. Whatever the reading is, both cylinders should be about the same. Big PSI differences between cylinders could indicate stuck rings.
When you remove the exhaust manifold to examine the piston and rings, also look at the cylinder walls for scoring or aluminum deposits. You will notice two or three vertical scores on the cylinder wall directly opposite the exhaust port. Don't worry about those. That is where the ring gaps are located and they will leave marks on the cylinder wall.
Sorry about the radiator size mixup. Your rads are bigger than the rotax rads.
Bill.
