I'm considering Doc's pin oiling mod >HERE< for my replacement castings and have a few questions.

What size are these drilled to and what about de-burring in the pin bore, is that an issue?



Also, I'm not sure if I'm understanding or seeing this right but it looks like two holes are drilled here in the pin boss area to intersect with the cross drilled hole from the oil ring groove; one drilled down through the pin boss and another one just outside of the pin bore, in the lower flange of the piston head, sort of looking like it would spray on/near the end of the pin? Is this correct and if so, is the second one near the pin end needed or just super over-kill? TIA

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1966 Coronet Deluxe

I tend to use 3 / 32 drills for this. (.093)

You need to get a drilled passage from the oil ring groove to the pin bore... do it any way you feel most comfotable in doing.
The pistons in the photo already had a oil hole at the bottom of the pin boss so I went thru that hole, to access the other side.

Careful deburring, after drilling, is a "must" and doing the deburring actually takes me more time then the drilling operation.
DD

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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1966 Coronet Deluxe

Looks great, good drilling job.
The smaller hole is not a problem... that passage will quickly fill with oil from the oil ring groove and then has to pass thru .001 of pin clearance so there will be ample supply.

As for deburring, just remove all the loose material and chamfer the edges of the new hole, then check your work with the pin. All is fine if the pin passes thru freely.
DD

Thanks again, I feel a lot better about this now!

About the deburring, I also tried my usual shortcut by using a larger drill bit to put a small chamfer on the exit hole but because of the angle it sort of tore out on the side of the hole rather than leave a clean chamfer. I tried to get a photo of that but it doesn't show up, it's near microscopic but still bothers me. I think that's because the angled/oblong exit hole, I'm not working with a clean 360* opening. So back to my brass wheel idea; this seems to work fine and quickly removes the upset area around the exit hole allowing for a smooth feel on the pin going through, but I don't have a chamfer so I'm looking for advice there if you think it's absolutely necessary. I don't feel comfy using a stone or burr (for aluminum) in there and wonder if I'm better off just leaving it with a clean exit hole?

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1966 Coronet Deluxe

Start with a small round ball cutter or stone (Dremel), just over the hole diameter.
High speed steel, "single" or "double-cut", both work.
1/16 or 3/ 32 ball are the sizes to try. (ebag 350576995851 for 6 bucks)

A brake, wheel cylinder hone can also be of help but make sure it has fine stones and use it by hand... not powered by a drill.
Or roll some 600 grit sand paper around a dowel.
DD

OK, I'm on it, thanks.

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1966 Coronet Deluxe