guys, i have some aluminum heads from a 91 vette. i bought them from the guy who rebuilt my engine. he installed the heads on my 350 camaro engine. now i'm putting all the top end of the engine back on. i have everything all buttoned up. yesterday i was putting the plugs & wires in,and found that the cylinder #8 (the hardest plug to install,because of the headers)spark plug hole seems to be stripped,or crossed threaded.the plug will go in, and i can snug it up with my fingers but it will become loose again if i try to move the plug left or right,or up & down. i really don't want to undo all the top end and pull that head off. what can i do short of taking that head to a machine shop? my friend suggested wrapping teflon tape around the plug,but i'm not sure about that. what do you guys think? any replies will be greatly appreciated!

 

Use a Helicoil.

 

yeah, i never thought of that. i've never used one b-4, not sure exactly how to do it. do i use the same size as the hole or same size as the plug?

 

Take your spark plug to the parts store and tell them you want a helicoil kit to fit it.

 

thanks man, what do you think of my friend's suggestion? wouldn't teflon tape break down because of the gas?

 

No, but teflon tape is for sealing thread-sealed fluid connections. It won't do anything for your mechanical problem.

 

Also note that the spark plugs for those heads are a 3/4" reach, flat gasket seat. Which are different from the spark plugs that the iron heads used.

The Autolite 3926 are the stock 'Vette plugs. Probably be better to drop a couple of heat ranges and use the Autolite 3924 plug.

RBob.

 

Good luck getting helicoil into #8. It's not going to be fun.

 

Is it actually possible to get a helicoil in here without removing the head?

 

Is the engine in the car?

 

It may be possible, but I'd pull the head. It will be easier and safer in the long run.

 

Hey Apeiron, today i tried screwing a shorter plug in that #8 hole,and it snugged up finger tight and din't move. The original plugs that i was using are NGK FR-4's they have long threads which are supposed to be used with aluminum heads. the short thread plug i used was just an old Champian cast iron head plug that i had lying around. I wonder if i can just use a new set of AC Delco's that are designed for cast iron heads? The engine IS in the car, so trying to use a Helicoil or tap & die set is going to be a major pain!

 

no. jv9999, it wouldn't be easier to pull the head off. i recently spent a lot of time closing the top end up. putting on the upper and lower intakes, the alternater and all of the brackets, the distributor, etc... all of that would have to be undone to pull the head off.(maybe i'm just too lazy)

 

In that case, you could probably do it if you pulled the exhaust manifold.

 

Can you pull the header off use the helicoil then put the header back on?

 

yes. after explaining my perdicament(spelling?)to a buddy who has his own high performance shop, that is exactly what he suggested. in fact he told me to call him back when i have the header off and he will come over to tap it out for me. i'm glad i thought to call him. just got off the phone with him.

 

No you can't. A cast iron head has a tapered seat around the plug hole that seals with a matching tapered section on the plug. An aluminum head has a flat seat and the plug seals with an aluminum crush washer.

"Finger tight" isn't much of a test of the fitness of threads anyway.

 

yeah, i know. but if i tighten it with a wrench, i believe it will lock down. ok how about this, a plug thats designed for aluminum heads but have short threads like the cast iron plugs. is there such a creature?

 

There are, but if you use a shorter-reach plug, the spark will be firing back inside the plug hole instead of out in the chamber where it'll do some good.

 

so would a hotter plug solve that problem? you seem to be very knowledgable about this stuff, i'm sure you can figure out something for me!

 

No, plug temperature wouldn't address that at all. The right thing to do is fix the threads and use the correct plug.

 

i have a MSD coil and 6a box that i plan to install. will that help?

 

No. Fix the threads.

 

ok i guess i have to pull the header off and take care of this problem using a helicoil kit.
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thanks Apeiron, you have been very helpful, keep up the good work! by the way do you drag race?

 

The factory L98 AL head will accept either plug style, it just needs to be a long reach plug.

 

yeah Madmax, the problem is the long threaded plug won't lock down. i'm just gonna have to fix the problem like Apeiron said. good nite fellas. it's midnight here in Georgia now,and i do have to go to work tomorrow.