Join Date: Aug 2018
Location: New Brunswick, Canada
Motorcycle: 2011 GSX-R750
I drilled out a 12mm bung and tapped it for 18mm
On my 2011 GSX-R750, I successfully drilled out the stock 12mm O2 sensor bung--while still mounted on the bike (didn't even loosen header)--and tapped it for 18mm x1.5 thread pitch. First, I removed the stock sensor and put a 5/8" dowel 6 inches long into the hole to simulate the drill bit and see exactly where "straight" is. I could then use a corner of the crankcase as a landmark. (Note: If I had loosened the header, this marker wouldn't mean anything.) I then drilled it with a 16.5mm bit with a 1/2" chuck. I had to get a drill with a 1/2" chuck (most drills are 3/8") and a 90 degree elbow to drill around corners. Power Commanders require you leave the stock O2 sensor in place and drill a new bung hole and Bazzaz requires that it no longer be connected, so drilling the stock bung only works if you're going with Bazzaz.
Look, lean, and believe.
Last edited by Superbike Racer; 12-19-2018 at 09:34 AM.