Heilicoil question.

[Guest Anonymous]

Was looking at new aluminum heads for older Z28. One of the selling points is the fact that each spark plug hole contains a stainless steel insert to prevent stripped threads. This seems like a good idea for those of us who ike to swap plugs on the fly - without waiting for every thing to cool down.

I have an original, 30+ year-old, aluminum E12 head bolted to my 72. I have probably pulled the plugs as many times as I have stepped on the brake pedal. Sometimes (especially the early days) I swapped plugs when hot - but I have never had a stripped thread problem. Nowadays, I wince when tightening plugs.

1. Do you racers out there routinely helicoil your heads to eliminate this possible headache? Am I becoming over conservative in my old age?

2. I noticed one of the spark plug makers advertise that their plugs' threads' are cold rolled and plated to avoid seizing. Does this eliminate the need for a dab of antiseize?

Tanks

[jerry]

yes, you are becoming conservative in your old age. just keep your threads clean and use a torque wrench. i recently thought i had stripped a spark plug hole but it turned out to be dirty threads due to carbon buildup. a threadchaser cleaned it up.

as for coldrolled and plated plugs. that's marketing. the plating is probably either zinc or cadmium. cadmium has an inherent quality of actually being a somewhat lubricant (lubricious, is the term, i think) as it oxidizes.

use anti-seize, regardless.

[Guest Anonymous]

Does this mean that using a thread insert like "helicoil" is not treated as preventative maintenance by those racers who routinely swap plugs during the "heat" of competition.

[john_a]

Does this mean that using a thread insert like "helicoil" is not treated as preventative maintenance by those racers who routinely swap plugs during the "heat" of competition.

No, using a Helicoil is not a good PM for spark plug threads.

They may be suitable for other locations, where you don't want to wear out aluminum, but for spark plugs you want nothing in the way of heat transfer (from plug to head.)

It's a salvage repair for plug threads, not an upgrade.

[Guest Anonymous]

Wondering out loud. Perhaps this situation no longer occurs or might only occur between trips down a straight 1/4 mile. But allow me to put foot in mouth with this question.

After you have tortured a cylinder head by repeatedly pulling and reinserting sparkplugs while the head is still hot, what do you do at the end of the season (or maybe even the end of the race) for weak or "suspect" sparkplug threads. Do you heliarc the hole and retap it? Toss an otherwise good head?

Not to disagree with you, but could you not compensate for the less-than-terrific heat transfer of stainless insert by running different i.e, hotter plugs?

I also looked at an Edelbrock catalog which did advertise stainless inserts in their aluminum heads. It may be that plugs for those heads have shorter thread lengths than an E12 head and are thus more susceptible to stripping.

Again, just daydreaming at work. (Please Dont tell anybody)

[bevans6]

I agree that a helicoil for the spark plug is a repair, not an upgrade. I like to use anti-seize compound on the spark plug threads - sparingly! - and have never seized one. But I have seen them seized on high-mileage engines that have not been maintained. Probably the best thing to do is change the plugs every so often - that will keep any corrosion at bay.

I do have a head on the shelf where there were helicoils in two of the spark plug holes. When I took the plugs out, one was seized to the helicoil and it came out with the plug. The other was just bad - the plug wouldn't thread in any more. I used the solid plug repair inserts to repair the bad helicoil repair...

Brian