Ok, well first off. I'm converting a Chevy Caprice HeaterCore into a watercooling radiator.
Well, I wanna use 5/8" barbs. The barbs I have are 3/4" on the thread size...I HAVE to put these in the top of the rad for my case design. I sealed the previous rad holes with WelBond Glue (it's waterproof), and then crimped them off.
Well, the largest metal bit I was willing to pay for was a 5/8" bit. Which is fine, because when I build my waterblocks, I'm going to use a ring saw to cut off the threaded side of the barb, and solder it in place.
Well, I tried soldering on my radiator, but the fins' solder started to melt, and some of the fins were peeling away, so I decided that soldering was a no no.
So what I've done, is I drilled out the top of the rad with the 5/8" bit. But to get a start point done, I just use a small bit. (I'm using a radial drill press for this)
Well, obviously 3/4" won't fit in a 5/8" hole, so I used some tin snips to make 16 cuts and then bent up the "tabs" to make the hole bigger. Then I placed the threaded side in, and pounded the tabs back in place.
Since solder was a no no....I bought this great Ace Marine Epoxy from Ace Hardware. I then epoxied the barbs in place. I did it in two coats, just to make sure I had a nice even layer.
When it dried, I had a leak. So I added a third coat, still had a leak. I thought I just screwed up, and I couldn't fix it. Well, I thought about that UV dye lite to trace it, but I didn't wanna waste any just on a radiator... Then I thought about trying to shine a flashlight inside, to see if light came through.
Well apparently when I made my first pre-drill with the smaller bit, I punched through the bottom of the top part as well. So I have no filled one of the air flow holes with the marine epoxy, and it's a complete seal
Moral: If it still doesn't work the 7th time, keep screwin with it.