Getting ready to pull the heads and reading ahead a bit on things I need. I like to follow RAVE as close to the T as possible... so I suckered up and bought 4 new secondary air adapters from Rover Jaguar Parts @ $55/ea.

In RAVE, it says to clean the deposits using a 5/8"-20 TPI UNF 2A thread tap, which of course I can't find anywhere online as 18 TPI seems to be standard. Anyone know where to get one of these... or should I just have the machine shop do it when I take the heads in to be planed and valves re-sealed? I'm guessing they'd have that tool, right?

 

This will get the job done, but it ships from China and will probably take a couple of weeks.

https://www.amazon.com/Threading-Mac...s=5%2F8+20+tap

If you're pressed for time, or if you want the closest tolerance to the prescribed thread size and pitch, this is a good bet, albeit three times as expensive.

5/8-20 UNS, H3, 4 Flute, Bright Finish, High 04846143 - MSC

Good luck.