Shdggsdv

I appologize if this is a fairly beginner question, but I took my heads to a speed shop and they gave me this 3/8" pipe plug thing and said that'll work. Brought it back and found out that it only threads in 1.5 turns before it feels like it's crossthreading.

I measured it with my thread tester set and the 5/8" threaded in the hole no problem. I went to Oreillys and picked up a 5/8" plug and it didn't thread through?

I'm a little lost here and I'm sure I'm missing something. Here's an album showing the stuff

www.imgur.com/a/wBGBe

lars

They're pipe threads, and what they gave you is correct. A 3/8" pipe plug has threads which nominally measure .63, which is 5/8 (but they're tapered). Pipe threads will screw in about 2 turns and then jam up. That's what they're supposed to do. There is no such thing as a 5/8 pipe plug. If there were, it would measure about 7/8" on the outside.

Lars

Tim Ware

lars , obviously, is right. Pipe threads are tapered. But... the amount the plug screws into the head is determined by how far the tap was inserted during machining. By tapping the hole deeper, the taper increases. So you can thread the plug deeper if you re-tap the hole deeper. Be careful. You can actually exceed the recommended number of threads required for a good seal. I like about 3-4 threads.

cv67