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Spark Plug removal & temperature of head
Topic Started: Mon Jul 2, 2018 9:57 pm (130 Views)
Billy Smalls
Newbie
[ * ]
Hi
So I want to do a compression test and need to get the engine up to normal running temperature. That's fine, only there seems to be a big difference of opinion on taking plugs out hot. Theories about threads distorting etc. Most say remove plugs only when head is stone cold.

This is my first aluminium head, so thought I'd ask for comments or observation?

Cheers
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Greek Taxi
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More than part of things
[ *  *  * ]
No idea about hot/cold, but I'd do this:

Remove the spark plugs when cold. Clean up the threads and apply a smear of copper grease.
Put them back in - 11lb ft torque for the M102 engine.
Run the engine up to temperature.
Take the spark plugs back out.

This way, you'll only potentially face a problem of an over-tight spark plug that doesn't want come out when the head is cold.

Also, vacuum out the spark plug recesses - a lot of grit and other crap can fall down there. Tape a piece of hose to a vacuum attachment and you can get right in there.
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Billy Smalls
Newbie
[ * ]
Thanks Mr. Taxi - the plugs are now copper slipped and hand-tightened. I was super cautious getting them out, so used a little plus-gas and did in fact warm the engine beforehand.

Going to do the test tomorrow. The plugs are all nicely tanned with no oil or soot, so I'm quietly confident.

Cheers mate
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martinw190
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Part of things
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Good advice from Mr Taxi there. :)

You should find that most things come apart easier when hot anyway, so it's never been an issue in my experience.
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Billy Smalls
Newbie
[ * ]
Cheers. Only to say that putting steel plugs back into a hot aluminium head may not be a good idea as aluminium expands and contracts at a different rate to the plugs, so if attempting to unscrew when cold could be tricky? just a thought....I may be over-complicating things!! ha ha
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stwat
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You're over thinking this.
I've removed/replaced many plugs in these cars over the years, hot or cold I have never had any kind of an issue.
The main issue to be mindful about is the possibility of cross threading. But you seem mechanically minded enough to be able to feel if was starting to occur.
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Billy Smalls
Newbie
[ * ]
cheers, yes almost certainly overthinking things!! ha ha

I always start a plug-screw-in by turning the plug anti-clockwise to find the thread, wait for it to pop into the groove, then clockwise. I think most cross-threading happens when the plug is put in at an angle - you really have to lean down into the engine bay to ensure it follows the angle of the holes....and it can be a deceptively shallow angle....

and rest....
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