How to re-tap oxygen sensor threads?
 

Aftermarket downpipe, a couple of slightly damaged threads. Most of the threads are undamaged.

Anyone know of a good way to fix this without needing to weld in another bung? Is there a tap out there I could buy/rent/borrow for chasing them out?

Dave

you should be able to find a tap, but it's going to be pricy. all the good taps are usually carbide or something like that and since it's big it's $$$.

my suggestion is find a SS bolt that is the same size and work that in and out a few times with some lubricant.

The most damaged piece of thread is visibly rolled over. So I'm afraid I don't expect the sacrificial bolt idea to work.

I suspect I need to find a small head for a dremel that can grind away the damaged sections of thread.

Dave

Negative - here is the tap you need, 18mm x 1.50 thread. Here it is at Amazon - http://www.amazon.com/1-5-High-Speed.../dp/B0006G4N7Y. It is not that much.

This is a common tap. You could simply go by your local machine shop and asked a guy there to chase your threads. Take em a dozen doughnuts.

Later

I don't know what size tap you'd need...but I'm sure it is available. They are not that expensive. I think I have an old sensor laying around, I'll grab my metric T&D set and measure the threads and let you know if you like. Ace Hardware or Sears will have the largest selection of individual T&D's unless you live near a specialty tool distributor.

Sears also carries a fractional/metric thread chaser kit for $70, may have the size needed in that...can't cut threads in raw material like a T&D...but works well. A tap will cost you a quarter of that or less. Sears has a T&D metric 39 piece set (009-52383) for $100 that includes the M18 X 1.50...then you'd have just about everything you'd need for the car except for a couple 1.00 pitch T&D's...but I don't think Mazda used a lot of fine pitch threads.

Ah, Tom beat me to it...that size tap is common. Check the above sources...you can also check their on-line sites...free delivery to store if not available in store.

Another note, Helicoil (if needed) makes a repair kit for that size thread:

http://www.bollhoff-rivnut.com/en/de...r_helicoil.php

Just go down to your local Ace Hardware and buy a 18mm x 1.50 tap or you may be able to do the rent-a-tool deal at your local parts store for a spark plug thread chaser, which happens to be the same size.

Rock on. I was concerned this would be some obscure metric fine pitch tap.

I'm sure I can find someone with the right tool.