Damaged Spark Plug Threads

[Patman]

I'm going to change my plugs this morning, and have decided to go back to my old method of dabbing some motor oil on the threads.

Just need to decide which motor oil to put on them now!

 

[Motorbike]

Something about a steel insert I don't like is the real possibility of it absorbing an unusual amount of heat since it's a disimilar metal.

I like the heli-coils and the type metal and I lock them in on the O.D with locking agent so they will not ever back out when changing the plug .

Many years ago while indexing spark plugs on race motors I caught on to the fact some spark plug brands/types have threads that stick past the threaded hole and into the combustion chamber . When this is the case on street engines that get the plugs changed every 30k or so the ultra hard carbon can build on that last thread causing it to act like it's seized and pull the threads out of the aluminum heads when removing .

Some aluminum is tougher than the next one since the exact same make-up is not used throughout the industry . Some make for a better thread than others .

The steel inserts are the ticket where the exhaust flange holes are though especially with headers that are removed often .

 

[john_ertw]

When applying anti-sieze to the new plugs how much do you put on? Do you coat all of the threads all around or is just a dab of the stuff good?

 

[427Z06]

quote:

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Originally posted by john_ertw:
When applying anti-sieze to the new plugs how much do you put on? Do you coat all of the threads all around or is just a dab of the stuff good?

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I use a small stiff well defined brush and lightly paint the 2nd to 4th threads from the business end of things. You don't want this stuff to get onto the electrodes or porcelain insulator.

 

[Shannow]

I always use antisieze on the threads. A tiny dab, then work it into the threads with my fingers.

I use the metal based antisieze, and am very careful to heep it away from insulators and electrodes.

I'll help a friend out with a helicoil if that's the way they they want to go, but usuallyrecommend a heat range or two colder, as there are more interfaces in conduting heat back to the head.

If you had 128 2 3/4" studs inserted into valve chests, with antisieze (allegedly), then left them in place for 10 years at 600psi and 1000 degrees F, how many would you be able to unscrew easily ?

 

[427Z06]

quote:

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Originally posted by Shannow:

If you had 128 2 3/4" studs inserted into valve chests, with antisieze (allegedly), then left them in place for 10 years at 600psi and 1000 degrees F, how many would you be able to unscrew easily ?

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I would say (hypothetically) all of them.

 

[Shannow]

Close - 6.

 

[Hirev]

You would be amazed at how much more trouble free getting plugs out of aluminum heads is if you get the motor as warm as you can stand it. I learned this working on bikes in the 70s. Especially if they were tapped at the low end of the tolerances.

 

[XS650]

quote:

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Originally posted by Hirev:
You would be amazed at how much more trouble free getting plugs out of aluminum heads is if you get the motor as warm as you can stand it. I learned this working on bikes in the 70s. Especially if they were tapped at the low end of the tolerances.

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Conversely, don't tighten your replacement plugs util the heads are cooled off. The shrinking aluminum will get them in a death grip that requires you to take them out hot for sure next time.

 

[Hirev]

Also use a torque wrench to install them if you possibly can.

 

[sprintman]

Copper based anti-seize all arond the thread. I use Penrite which has a US distributor. On my 26th vehicle now and do most of my own maint.

 

[427Z06]

quote:

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Originally posted by Hirev:
You would be amazed at how much more trouble free getting plugs out of aluminum heads is if you get the motor as warm as you can stand it. I learned this working on bikes in the 70s. Especially if they were tapped at the low end of the tolerances.

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Unfortunately, what you recommend is hard to do on this engine. You have to take off too much stuff off the top of the engine to get to the plugs. It was 94F ambient when I pulled the plugs.