If you are having to do that you are using the wrong taps. Spiral tap and spiral point tap allows you power tap it, means using a machine to drive the tap in directly and it’s much faster than turning back every 2 turns.
But if you just need to chase the thread then a form tap should do the job. Form taps do not cut, it just uses pressure to form the thread. I was able to restore worn out thread this way.
But for spark plugs you really want to take the head off to be safe, so you don’t end up with chips in the cylinder. Worst case you may need to helicoil it.
Gotta talk to machinists if you need to tap holes. You can easily get taps here, there’s a shop near Taipei bridge MRT station that sell used taps cheap, if you need big sizes that might cost an arm and a leg especially for a one off job. They got lots of different sizes, from M4 all the way up to M25+ and their imperial equivalent. Taps run anywhere from 40 to 300nt each, depending on size and weight (they sell HSS tooling by weight). Taiwan is only terrible for woodworking stuff. Being that Taiwan does lots of manufacturing machine tools are in excess.
I like this idea for starting a spark plug into its hole:
I’m assuming you have access to an air compressor in order to clean out the cylinder after thread chasing. What would be cool is if you could get one of these dual use air guns with a custom tube small enough to go thru the threaded hole so you can vacuum rather than blow into the cylinder:
I got a “FORCE Professional Tools” Spark plug hole thread chaser in the nice Kaohsiung tool shop.
(its not actually the best Kaohsiung tool shop, but the laoban in that one gets a bit trigger happy with the M word when shown pictures without the correct Japlish “Comin in ere with your fancy foreign fantasy tools” stylee, so I tend to leave it till last)
350NT
“Applying company with 13/16"standard deep socket” which American atavism seems to be about 21mm in the modern world.
I’ll probably try it tomorrow if I can find the socket. If it’s no good I’ll probably try carving up a spark plug.
Hoping shaving foam and grease will limit chip ingress, though I’d be happier if I had compressed air to blow it out.
Thanks. Unfortunately I don’t have a working compressor.
I did mostly rebuild a scrap one a while ago, but it needed a couple of compression fittings, standard industrial components, on a made-in-Taiwan compressor, but fittings that no one in Ktown would admit to ever having heard of…
And the shop is going to charge big bucks to fix it. If it were me I would remove the head and do it that way, and who knows what other parts are damaged.
that’s about 60,000 right there.
The car’s probably worth 10,000nt if you sell it to a scrap yard.
If it only had 2 cylinders firing before this you might as well take it apart yourself. Maybe do better to just part it out yourself.
Can you post a photo of this lovely auto that has us all so concerned?
Had a 71 Mercedes 220D blow an injector into the cylinder. Banging like crazy. Immediately took it to the experts. They said nothing was wrong. Kept banging and they scoped it finding the injector.
I think they were able to avoid removing the head. I can’t remember but it was quite fine after. I’m guessing your block is a little softer.
