The Stovebolt Site Forums The Shop Area Engine Shop helicoil on oil galley?

Well I did something stupid. :o While doing the full oil conversion on my 235, I was tapping for the plug on the front of the oil galley. I thought I was perfectly straight while running my tap into the front oil galley, turns out I was not. I ran the tap in approx. 1/4 inch before it went tight. The plug will only go in about two threads before it gets really tight. My thought is to drill it and put in a helicoil type insert. Maybe I should just drill to the next size up plug. Any suggestions? Has anybody made this mistake?
Thanks jason

Did you use a bottoming tap so you cut enough threads for your plug? If you were using one of the other two most common type of taps did you hit an interference (something on the other side of the hole) before the thread was fully cut? I assume you are tapping a NPT type thread.

Thanks beltfed, No I did not use a bottoming tap. maybe that is the reason the plug is not going in all the way. I did not see any obstructions keeping me from going any deeper with the tap. tap is for 3/8-18 npt.

jason,

If you were indeed using a pipe tap as beltfed mentions, and your tap drill size was proper, the pipe tap has to go in a whole bunch more than it appears to the casual eye for the plug to fit properly. They make short taper pipe taps for situations where there is an obstruction that would prevent a standard pipe tap from achieving full (almost) penetration .

Does this make sense!

Stuart

Thanks Stuart,
One thing I did that I am know questioning is not drilling the oil gallery, as I thought this was the proper size already. This might explain the tap binding up on me, if the hole was to small.

Helipackmech,

The hole must be drilled the proper size for the whole deal to work right..especially with a tapered pipe tap. Because your tap only allowed the plug to go in two threads or so, it might be possible to drill the hole the proper size, then tap it again with the same tap. I don't think I have seen a Heli-coil in a NPT configuration.

Stuart

Stuart
Where I got off track on the drilling is when I removed the freeze type plug from the oil galley it had 37/64 stamped in it. The 3/8 tap needs a 9/16 drill bit from what I understand, so I just figured it would not need drilled. I did find a helicoil insert kit from msc indusrtial supply co. I will try to drill an re-tap first.
Thanks Jason

Grind the first 2 or 3 threads off the tap. Re-insert it into the hole you've already tapped, and work it in about 1/4 turn at a time with lots of lube. I've got a a set of modified taps I use for threading the ends of oil galleries on smallblock V-8's. The hole needs to be opened up to the size that will allow the plug to engage several threads. Use a sealer, or LocTite, and don't over-tighten, as you can crack the cast iron with a too-tight tapered plug.
Jerry

1.Make sure tap drill size is correct. Run a 9/16" drill in the hole. Likely problem is undersize hole.
2.If there are no obstructions in the bottom of the hole use the tap you've got and it needs to go in at least 2/3 of the length of the teeth on the tap. Then snug a pipe plug in there and back it out counting turns. If it goes 3 turns and then falls out it's perfect. If not go in with the tap again. Back up and use lubricant each turn as npt threads rip easily.
3. There is no such thing as a bottoming npt tap but as Stuart pointed out they are available if you ask for a short projection pipe tap. This is the same thing as Hotrod Lincoln is talking about but if you are unfamiliar with reconditioning drills/taps buy one as no clearance can result in a broken tap in there.
4. If it's completly thrashed go up to the next size and use a reducer. Even if a npt helicoil exists it will likely leak.

Good luck.

Curt B.

I stand corrected by I.B. Hoggin. It is indeed a 'short projection' tap. Sorry for any confusion.