Impact to remove spark plugs

[willbur]

Greetings All-
seeking opinions/advice regarding using an impact wrench to remove very tight spark plugs in an aluminum head. Been in for 19 years- but only 41K. If I mess up on this, alot of work removing head for repair or buying new.

 

[Hall]

Have you already tried with a hand tool and know they're "very tight" or you just presume they will be ? Got them soaking in penetrating fluid ? I think it's Eric from S Main Auto that uses an impact on some infamous Ford 3-valve (???) heads. Apparently it's almost normal for the plugs to break off in these but he's had better luck using an impact and they not break.

 

[Lapham3]

I used my low torque right angle Milwaukee impact to vibrate them a bit and break them loose. Did that just once with a situation similar to your situation.

 

[joekingcorvette]

Blow out the plug area with compressed air. Soak them overnight with PB Blaster. Use a hand wrench and turn them about 1/8 of a turn to loosen the plugs. The tighten them back about 1/8 of a turn. Keep going back and forth and they should come right out without damage to the threads. I did this on my 05 Ford F-150 5.4 and didn't break any of them.

 

[IndyIan]

A few bangs with a weaker electric impact would probably be beneficial, I've done it with a transmission plug in a cast aluminum pan, went back and forth a few times, and it finally popped loose, and left the threads in the pan.
Just letting a 400lb+ electric one go full tilt in one go with no penetrating oil might not work out so well...
Electric ones usually hit harder for their ratings, than air, due to the design of the impact mechanism, so a 200 ftlb one has a sharper strike. I know on my drain plug I had a 2' breaker bar and was getting up near 300ftlbs on it and no budging, but my 200ftlb impact got it with no damage after a few 1 second pulses looser and tighter, its just breaking the corrosion layer.

 

[totegoat]

Why replace at only 41K if the vehicle runs fine?

 

[Dave9]

^ Possibly because if they don't come out now, they never will and eventually that'll be a problem. Plus if it's been 19 years, might have an unusual driving cycle with lots of short trips, where there's more deposits than the average 41K plugs would have.

I'm wondering about access, if there's room to get an impact wrench in then is there a good amount of work area?

I just wouldn't want you to get burned, but if the engine still runs, the coefficient of expansion is higher for aluminum than a steel plug thread so heating the engine up a little should help. Very warm, but not hot. At the same time you always want the engine cold again before putting plugs back in.

I wouldn't use an impact because that's less control over the amount of torque than doing it by hand. That's unless you simply can't generate enough torque by hand... comes back to access again, a straight shot to them on an inline 4 cylinder can be easier than something like a V-engine with a tight engine bay, where you can just use a longer breaker bar.

You can also use a hammer to gently tap on the breaker bar, apply some more penetrant, wait, repeat.

 

[Tman220]

At that age and 41K it seems to be it's a seasonal, nice weather type of vehicle which doesn't see a lot of rain, or salt. What makes you think you will have any trouble removing these spark plugs in the first place? Unless it's a 3-valve ford modular??
I would personally give it a shot with a socket and elbow grease first. An impact will almost guarantee damage to the threads if they are indeed stuck, which I doubt given the mileage and age.

 

[Barkleymut]

what kind of car/engine are we talking about?

 

[atikovi]

^ Possibly because if they don't come out now, they never will and eventually that'll be a problem.

Time to sell it then.

 

[tnt_motorsports]

I have only ever used a socket and ratchet to install and remove spark plugs. FWIW I anti-seize plugs when they go back in as well.

Just my $0.02

 

[Jimmy_Russells]

Have you tried when the engine is hot?

 

[atikovi]

Have you tried when the engine is hot?

Metal expands when hot. The plug will expand inside the hole. The head will expand tightening around the plug. Probably not a good idea, especially on aluminum threads.

 

[Jimmy_Russells]

Metal expands when hot. The plug will expand inside the hole. The head will expand tightening around the plug. Probably not a good idea, especially on aluminum threads.

Ahh yes so this is why when people have stuck bolts they use liquid nitrogen to free them up

/s

 

[atikovi]

Ahh yes so this is why when people have stuck bolts they use liquid nitrogen to free them up

/s

That's a new on on me. Will have to check Autozone or NAPA and see how much a gallon nitrogen costs.

 

[Dave9]

Metal expands when hot. The plug will expand inside the hole. The head will expand tightening around the plug. Probably not a good idea, especially on aluminum threads. ... That's a new on on me. Will have to check Autozone or NAPA and see how much a gallon nitrogen costs.

The opposite. Yes the plug will expand but being steel, will expand less than (coefficient of expansion roughly half as much as) the aluminum head. When the head expands, any holes in it do as well.

Rather than nitrogen, the cans have something else (HFC-152a refrigerant, solvents and oils), but same purpose, freeze spray to reduce fastener temperature to contract it.

https://www.autozone.com/greases-and-gear-oil/lubricant-grease/p/crc-freeze-off-super-penetrant-11-5oz/898352_0_0

 

[atikovi]

The opposite. Yes the plug will expand but being steel, will expand less than (coefficient of expansion roughly half as much as) the aluminum head. When the head expands, any holes in it do as well.

Then why does nearly every manufacturer say to remove plugs from aluminum cylinder heads when the engine is stone cold? And why do you assume the plug hole expands when heated? If the aluminum around the plug expands, why wouldn't it expand inwards toward the plug? That would be the path of least resistance.

 

[Dave9]

^ Because the manufacturer doesn't want the liability of someone burning themselves, and they probably assume the person would then install new/cold plugs in a hot engine which is a no-no, will be overtorqued. There's also that the strength of aluminum starts decreasing with temp rise, past a certain point but I couldn't tell you the specific temp for whichever alloy is being used, other than that if it's not really hot, it can't be too weakened yet or it would never hold up in engine use at full temp.

I don't have to assume plug holes expand, this is basic physics that it will. Heating slightly decreases density while a hole getting smaller would require an increasing density.

https://physicstasks.eu/2107/change-in-the-metal-plates-size-during-heating

 

[atikovi]

^ Because the manufacturer doesn't want the liability of someone burning themselves, and they probably assume the person would then install new/cold plugs in a hot engine which is a no-no, will be overtorqued.

No, it's so you don't tear out the aluminum threads in the head.

I don't have to assume plug holes expand, this is basic physics that it will.

https://physicstasks.eu/2107/change-in-the-metal-plates-size-during-heating

I would think a cylinder head on an engine is a whole different scenario that an unsupported metal plate. The head is clamped down with 8 or 10 bolts to hold it firmly in position.

 

[Dave9]

^ That's only if you get the engine too hot, then not for the reason stated in the video but rather that it softens the aluminum.

How the coefficient of expansion affects a hole in a piece of metal is universal, the hole will always expand. The head is clamped down, but don't you think that what it's bolted to, is hotter still and also expands? It has to be engineered to allow for that or else things break and/or fasteners loosen.

You can test this yourself, find a piece of cast aluminum (whatever), and put a hole in it just large enough to put a fastener through, then notice increased slop after heating it. If you heat the fastener to the same temp too, then it has to have a lower coefficient of expansion, like a spark plug's steel threads do vs aluminum.