Technical Stripped spark plug hole thread...

[Pugglt Auld Jock]

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Expanding taps were patented in 1870

If you don't know they exist, you don't know to look for, ask for them, I guess the back tap became popular with the rise of aluminium heads 1990s

Looking at the prices £5 upwards, Sealy ones are around £15

I've come across expanding reamers and used them, but never thought about an expanding tap. I first saw this type of expanding tap some years ago, which, of course, is intended very specifically to clean plug threads and overcome the swarf problem. However an expanding tap for use in the normal way? Never knew they existed. Every day's a school day as they say.

 

[velvet]

They should go in dry if you are going to torque them up using a torque wrench

Oiled will over tighten them and risks damage

They are coated, no need to oil read link in post 5 should explain everything

Start them by hand they are at an angle



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although even with an ali head , it can feel dry and stiff..as you say too much is no good