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Discussion Starter · #1 ·
Recently I was changing the plugs on my daughter's car, which has factory aluminum heads. I noticed a sticker warning not to change the spark plugs while the engine was hot or it could warp the heads. Is this really a concern?

I'll be doing a compression test on my 289 in the next few weeks, and I was planning to get the engine up to temp so the pistons and rings would seal well. Could this possibly damage my heads?
 

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I've never heard the head warping theory on doin plugs on hot aluminum heads. I have however seen the plug holes stripped out, because the aluminum expands so much more than cast when hot, it clamps down on the plug itself. Good hard twist, and pop, no more threads and your off to the machine shop for a repair.
 

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Discussion Starter · #3 ·
It was several weeks ago that I saw that warning sticker, and I think it may have stated it would "damage" the heads rather than "warp" the heads. Based on your info, stripping the plug holes might be what they were referring to.

Do any of you with aluminum heads avoid pulling a plug when the engine is hot?
 

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Striping in aluminum is common because it is so soft. Heating it only makes it softer and since it expands, the hole will actually be too small for the plug, causing at least a removal of some of the threads if not a complete stipping of the hole.

If you do by accident strip a hole, the head has to be removed and a steel sleeve put in it's place. I actally put a sleeve in each one of my heads before I put them on 351 because I didn't want to deal with the problem.
 

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how much did it cost to have the spark plug holes sleaved, I am looking to doing this on a set of my heads since they are for a street motor one less thing to worry about
 

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It cost about $20 for the kit with the tapping tool, and about $20 for all 8 sleeves. Lots cheaper/easier than removing heads and doing it to just one plug hole.
 
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