Another option is to use an old piston with an old top ring installed. Put the piston to be gapped in the cylinder just almost at the top of the deck. Use the old piston to press the ring into the cylin-der until the uncompressed ring in the piston stops you. Now the ring should be square to the cylin-der bore. Of course, this only works with flat-top or dished pistons where the ring you are pushing into the bore can make contact all the way around the top of the piston.