I thought these things were supposed to be a breeze. But the piston will not go in, even with some gental taps. It stops right at the first oil ring.

D16Z6 75.5mm overbore. Vitara pistons, 0.0035 p2w.

The piston slides right through the ring compressor without issue if it's off the block.

 

Continuous downward pressure on the piston while doing a swirl motion with the ring compressor. This will walk the rings into the bore.

Not a twisting but a swirling.

 

I think I found my issue. My machinest put no chamfer on the block.

 

Shouldn't need a chamfer with a tapered ring compressor as you have. A bit of finesse with the tool you have will get it to go.

Make sure your rings gaps are correct.