I need to install a 1/2"-14 bushing (reducer bushing 1/2" to 1/8") into a hole in a GMC engine block. I purchased the recommended 45/64" drill for the 1/2" NPT tap. The bushing is tapered - and I can thread it into the tapped hole about (barely) 3/32" to 1/4" in. However, it protrudes too far from the block surface and I would like to turn it in further for a closer but not flush fit.
(the tap only makes it into the hole about 3/8" at best possibly less)
This bushing is placed on the block forward of the fuel pump, and it serves as the drain hole for the oil filter mounted above there. If I can thread it deeper into the block I can have a straighter line from the bottom of the oil filter to the reducer and eliminate a 90 degree bend or reduce a possible constriction for the oil to drain into the block.
The issue I have with the 45/64" drill bit is that it easily slides through the existing hole and therefore the diameter is not large enough to turn the tap or the bushing deeper into the hole. I will need a slightly larger diameter drill bit (or a tapered hole) rather than 45/64 - and wondering if a 23/32" tapered bit would be the preferred option. Or, is this risky? and I should try to come at this oil drain problem from a different approach - and problem solve the drain line and live with a bushing that is proud of the block 3/8 to 1/2"
Questions:
Is there a tapered drill bit that can account for the taper on the tap and bushing so I can thread it further into the block?
Or, is there a un-tapered 1/2"-14 bushing that would thread further into the block? I plan to use a thread seal on this.
Is this what I need to accomplish the task?
https://www.ebay.com/itm/45-64-HSS-Taper-Length-Drill-Bit-DWDTL45-64/133299922924?_Last question: Are these tapered bits 45/64" at the point or do they taper from a smaller diameter at the point to 45/64" ?
Need advice from the experts about these things. Appreciate the help.
Tom
