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You need to remember the 4 cycle engine has 720° of crank rotation. There's Intake, Compression, Power, and Exhaust. So the piston is at TDC twice. Once is the end of the exhaust stroke. Once is the end of the compression stoke. If you watch the cam, the first lobe at the front of the block is cylinder 1, exh lobe. The second is the #2 exh valve. The 3rd is the #1 intake lobe. So watch as the piston comes up. If the pointed part of the 1st cam lobe is moving from pointing up to down when the piston is coming up, that's the exhasut stroke. The intake lobe will be coming around and heading "up" as the piston moves down after the exh stroke. When the piston beings to rise again, neither point of the lobes for that cylinder will be "up". Meaning the cylinder is sealed. That's compression stroke.