Spark Plug Tap.... What size tap??

[MIZZOUNNC]

I had a spark plug back out. The first 4 to 5 threads on the spark plug are worn down. A new spark plug will not start on the treads, meaning, those need to be rethreaded.

I have searched without success here, to find the tap size. NAPA gave me a 14mm which appears to be too small.... it threads in, but its loose. Does someone know the correct tap size?

 

[OneRedNSX]

I would think you would actually be looking for a thread chaser and not a tap. The tap will have a tendency to remove additional material (not what you want, could result in making things worse) but the chaser is designed to clean up / re-align existing threads that may be damaged. I would imagine that a chaser would also create less debris for you to worry about since it is not 'cutting' anything...

They make chasers that are specifically for spark plugs and you can get them at most automotive stores. Just double-check it with your spark plug size.

Personally, I think the guy at NAPA is not too knowledgeable about what he is talking about and almost made a big mistake giving you the wrong tool for what you want to do... That might be acceptable practice when you are working on a 5.0 mustang head where you can buy another one for less than the tap costs but I would never resort to using a tap on a nsx head!

Maybe somebody else can chime in here and give their opinion...

 

[EdinKali]

If some of the threads are damaged I wouldn't bother just chasing it. You may risk it blowing out later on down the road.

I suggest using a thread-sert/heli-coil made specifically for spark plug threads. It can be done without removing the head and is a permanent and reliable fix.

 

[Honcho]

Heli-coil for sure.

 

[OneRedNSX]

Yea, if its too far gone to repair the threads heli-coil is definitely the best way to go.

 

[A.S. Motorsport]

+1 on the helicoil common repair procedure.

 

[ralph cerbone]

Check out tool K&D 2125 ,it is a thread chaser ,with four threaded sleeves (3/8,7/16,1/2,3/4 ) you chase the damaged threads ,install the appropriate sleeve on the spark plug (ours would be 3/4), they give you a loc-tite compound to put on the outer threads of the sleeve ,you then thread the plug in to seat the sleeve ,remove plug to make sure the sleeve is seated , it worth a look !