Pulled my spark plugs and inserted PVC pipe threaded stubs while I cleaned and painted my 26/27 engine. During reassembly, I removed the PVC plugs and started to insert my plugs. All were very snug going in and just felt "gummy" and I wasn't comfortable that I had them all seated properly.
I pulled them out and made sure the threads on the plugs were clean. I felt the threads on my head and they felt clean. I got a short piece of gas pipe that was the correct thread and ran them down through the head. start easily and then very tight. All pistons were somewhat down in their cylinders, so I wasn't concerned about running a pipe down into a picton head, but I never got the feel that I was all the way through the threads. My first 3 cylinders felt better and the plugs seem to go in further, but I don't know how to tell that they are "all the way" in. The 4 plug doesn't feel like it's going in as far as the first three.
What's the best way to make sure my head threads are good and clean and that my plugs are correctly seated.
I'll hang up and listen, but available to answer any questions.
Clean the threads up with a 1/2" NPT pipe tap. Any hardware or plumbing store will have one. Probably your local Napa parts house too.
Robert, the stock threads are pipe threads so they are tapered, as long as they go in good and snug there is really no worry about the depth. I use a little pipe dope on the threads for sealer and have no problems. Without sealer of some kind(many opinions on this forum) you may have some blow by around the threads which will cause some oil pumping. As for cleaning just get a 1/2 inch pipe tap and go easy, no use in making it go all the way through, just enough to clean the threads. Good luck. KGB
Robert, Those threads are 1/2" taper pipe and the plug will not or should not go all the way through the head. They are meant to gradually tighten as the tapers mesh. They should not come to a dead stop like more modern plugs. Hope this makes sense and helps you out. Jim
If it's stock it 1/2 inch pipe thread. Pipe thread is tapered, the plugs will only go so far and get tight. There should be no way to run a piece of 1/2 inch pipe in so far as to hit anything, you would run out of threads on it before hand. You are not trying to get all plugs all the way down, just till they are tight. Then stop.
RE; 1/2 inch pipe tap, if you use one, you are only looking to "CLEAN" the threads not cut new ones. I would just put the plugs in as it sounds like the threads are fine.
Keith and I were typing at the same time but to clean the threads you could also take a piece of pipe or an old plug and grind or cut grooves across the threads so it would act as a tap. Jim
Great, guys. Thanks for the comfor level. I guess I was imaginiing modern plugs where they bottomed out againt the seats.
I did the pipe thing and gut two grooves in the threads with my angle grinder so that it would be able to push out any debris.
The plugs are 80 percent or so in their seats when they start getting snug, so it sounds like all is kosher. The thread dope or perhaps plumbers putty in the threads sounds like a good idea to prevent any blowby. Another thing unique to the T.
Thanks for putting my mind at eas that my spark gap would be all over the place and affect the timing or combustion.
Now, when that new timer arrives, I can wire it all back up.
"The thread dope or perhaps plumbers putty in the threads sounds like a good idea."
The "thread dope" is OK, but please don't try "plumbers putty" as it will harden up.
The best way to clean up spark plug threads is to make a "thread chaser" tool from a worn out spark plug. You can cut two or three notches in the threads at 90 degrees to the thread direction. Then use a bit of motor oil to lubricate your tool. Tighten it slightly more than you would tighten a spark plug. It will clean out the rusty threads and cut them a bit deeper.
The best way to clean up spark plug threads is with a pipe tap.
If the threads are really bad:
Rental stores usually carry a wide variety pipe thread taps along with the other plumbing tools that they rent out.
For a few dollars, you can rent a pipe tap instead of paying $50 to $70 or more for a new one.
I've rented pipe thread taps to clean and chase threads when I've done plumbing work around my house.
Also, for a spark plug I think anti-seize from the auto parts store might be a better option than pipe dope. However, I am no expert.