Thanks Doc. My pistons don't have the sturdy pin bosses like the one in your photo, so I decided to drill it in one shot, at angle from the bottom of the ring groove upwards to the pin boos. This required a smaller drill bit to obtain a good angle while avoiding nicking the top of the ring groove (actually I still did, you can barely see the nick in the second picture). The size I decided on is about .060", so please tell me if you think it worth the effort at this size, I thought it would be OK to go smaller since I don't have the restriction of the 90* intersection that yours shows.
Now, what's the best way to de-burr these holes? I erred on the light side for this practice hole by using the worlds softest brass wheel, the tiny kind that are made for dremmel tools, but I mounted it in a standard die grinder with a fine throttle control on it so I could take it easy. The burr in the pin bore came off with little effort so I doubt I did any damage or enlarging of the bore. The handful of pin bores I measured on these pistons seemed a wee bit tight to begin with, but I struggled with getting a good feel for the made in Chinexico snap gauge I was using for that so who knows how accurate I was. I know for a fact one of the pins actually felt tight though. Any fears here? Am I ruining these things?
You can see my first attempt was a little cockeyed, it came through at a slight compound angle but I think I can fix that for the others. Either way, I think the oil will get there no?
I was shooting for the best angle up to the pin boss so that meant going in from the very bottom of the ring groove. I'm not sure if this is a big deal, but I think the lower scraper ring will partially block this hole right??
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