Drilling holes in piston. The holes seem a little bit too large due to the chamfering. 5mm drill. A drill of 1 or 1. Apr 3, 2013 · Put the piston on the rod and slide the cylinder on. A move that I've used for years to control heat in ported vintage chainsaws. Dec 27, 2015 · I looked at a highly modded 809 today that had a hole drilled just under the rings on the intake side. Jan 22, 2018 · The punch marks were then spot drilled on the Dore Westbury miller and then drilled through with a 1. It looked to be about 1/2 inch hole. Thanks for watching!! Mar 9, 2007 · If you have a bridged exhaust port, and that bridge has not been relieved, you should drill the holes. This is common on cylinder reed cylinders but never seen this on a case reed engine.