Yes, I've searched and found many threads on cross-threaded spark plug threads. I do plan on buying a spark plug chaser. The one thing I didn't find is what size to buy. Are there only one 'size' threads on these things that include both types of spark plugs? Both for standard and resistor plugs?

I have the rear trailing plug that the threads are messed up. Either they were that way from when my son bought the car, or he did it. Not sure. Doesn't matter....well - it sort of does.

When he tried to put the new plug in, he only got it about 1/4 to 1/3 of the way in, so the threads furthest in should still be OK. That's why I was thinking the chaser might work.

And, since there is so little room in there, would one be a good one to buy?




And, how do they work? Does it expand somehow with it inserted so you can use the back threads and remove the chaser, cleaning the threads outwards as you go? I thought that's how it was explained on some other rx7club.com threads, but the picture above (and link to that amazon page) looks like a regular tap, doesn't it?

 

Thats because it is a regular tap. I would say that in the location its in, you are SOL. Unless you remake the thread, but thats a different thing


I have yet to find a way to start
from the inside out.

 

How about one instead?

 

Let me explain: Since you said the thread is messed up on the trailing, you effectively have only one side to work with; thus you cannot chase it. You can rethread it with an insert: helicoil i think

 

You can chase the threads and clean them up with a tap but it's going to be tricky to make sure the tap is going in straight. If the threads are beyond straightening you need to install a helicoil. You're in a bad place! Goodluck.

 

I am not sure what you mean by 'only having one side to work with'. And I am confused since you say I cannot cannot chase the thread, but another thread just above says I can with a tap. Will the end of the thread chase tool not fit in the opening? Still not understanding why the tool won't work.

 

Does the spark plug go in wrong everytime you try putting it in? If so, then the tap will more than likely also go in wrong. You want to start from the inside but that cannot be done as the other end of the of the sparkplug ends as a pinhole.
It can be done if you choose to try anyway but the chances of messing up the thread even more are very high

 

OK. I understand now why the thread chaser won't work for the trailing spark plug.

I have an idea for a better spark plug thread chaser for trailing plugs on the rotary engines.

The plunger/spreader is INSIDE the tube instead of at the end. This one doesn't have to go all the way through the 'head' like the one I bought.

There are only 2-3 threads at the end of my design so you can put it in as far as possible without hitting any of the bad threads. You tighten the **** to push the plunger/spreader towards the end of the device, spreading apart the 'splines' to match up with the good threads deep inside. Then, turn the device counter-clockwise to clean/straighten out the threads.

 

The only choice you have is threading it through that same side. First off, how deep are the threads cross threaded? If not all the way then you have to thread that took in straight, as your tapping hold it straight as possible and most of the time you can get it to transition with the existing threads.

If the threads are completely screwed, I really like time sert over help coil, but I'm not sure if that blind hole will keep you from installing one.
I would use some type of sealant on whichever thread insert you end up being able to use. I'm not sure what would be best in that situation, a special loctite?

Also keep in mind there are bottoming taps you can purchase that can tap almost all the way to the end.

Some heavy wheel bearing grease on taps can help keep shavings on the tap. Also maybe if you can do this process with a cyl leakage tester with air pressure to keep shaving going into the rotor.

 

Oh, and to keep the tap going straight I use a tap holder that fits on a ratchet and i turn at the head of the ratchet, not the handle

 

Whew!. I finally got the spark plug in straight.

I did modify the thread chaser similar to my drawing above. That helped get the tool started straight, and it worked enough to get the plug in. I was actually to turn the plug in by hand pretty easily as if the threads were never bad.

Thanks for all the suggestions.

On to the next project on the car: putting in new carpet...