Real risk of head damage when changing spark plugs

[rationull]

People warn all the time about overtorquing or cross threading spark plugs in aluminum cylinder heads. The service manual for my car calls for 18 ft*lbs of torque on the plugs which isn't a whole lot but it's enough that you've got to snug them pretty good. I always use a torque wrench on them so I feel like I'm safe but the fact that people make such a big deal out of it makes me extra careful anyway.

Is it really that easy to screw this up, or is it just a problem when you don't screw them in by hand first and then proceed tighten them as hard as you can with a half inch ratchet with an 18 inch handle?

 

[cchase]

It's easier to take the time to do it correctly than deal with the consequences.

Aluminum is soft, so the risk of stripping or cross-threading is high (if you don't have a good sense of feel).

 

[Smokefan1977]

Its really that easy, especially with 04-08 F150 5.4L engines. I torque everything that has a spec when doing a job

 

[bepperb]

I think it's more common for the plugs to corrode/weld themselves to the head and cause damage on the way out, than for a person to damage them on the way in.

 

[Astro14]

Originally Posted By: bepperb
I think it's more common for the plugs to corrode/weld themselves to the head and cause damage on the way out, than for a person to damage them on the way in.


Amen...very common, the longer they're in the head, the worse the problem. Further, if you use an antisieze compound that lubricates the threads, it's easy to exceed the strength of the threads near recommended torque...

 

[JOD]

Originally Posted By: rationull
People warn all the time about overtorquing or cross threading spark plugs in aluminum cylinder heads. The service manual for my car calls for 18 ft*lbs of torque on the plugs which isn't a whole lot but it's enough that you've got to snug them pretty good. I always use a torque wrench on them so I feel like I'm safe but the fact that people make such a big deal out of it makes me extra careful anyway.


That feeling of safety is just that--a feeling. It certainly isn't reality, particularly when you're threading a spark plug into a used cylinder head. What are the conditions of the cylinder head threads (generally, there will be less friction on an older head--but how much??)Are the torque values specific to the coating on the plug threads?? Unless you're using an OEM plug, probably not. Plus, add in the variance in friction torque common to all bolted systems. No thanks on using a torque wrench to tighten spark plugs.

Personally, I think the angle torque guidelines here are a lot safer: http://www.globaldenso.com/en/products/aftermarket/plug/basic_knowledge/installation/index.html

That feeling of safety while using a torque wrench has resulted in a lot of broken stuff (I can't say cylinder heads specifically, but in general). It implies a level of precision which simply isn't there. If torque wrenches came with error bar readings which accurately reflected their variance, I bet we'd see a lot fewer people using them, and a lot more people looking up angle torque specs.

As far as spark plugs either stripping or shooting out of the head, it really seems to be a problem common to a few models of cars, so I think it's a cylinder head design issue more than anything.

 

[qdeezie]

I think it depends on the engine and your "feel" when tightening them down if you aren't using a torque wrench. If you've done it for years and years, you know the proper "feel" when it's tight enough.

 

[Astro14]

Originally Posted By: qdeezie
I think it depends on the engine and your "feel" when tightening them down if you aren't using a torque wrench. If you've done it for years and years, you know the proper "feel" when it's tight enough.


mmmm....my feel comes from having exceeded the limit a few times and feeling that sickening reduction in resistance...I'll stick to the wrench, checking thread condition...and reduce applied torque by 10% when using anti-sieze...

 

[Trav]

Try a little (very little) never seize and 15ft*lb. Make sure you use it only on the threads and start them by hand.

 

[Boomer]

An old trick to avoid cross threading when screwing in a plug...put a length of small ID rubber hose (vacuum line typr) on the end of the plug where the spark plug wire attaches. Now insert the plug into the threaded hole and trun the rubber hose gently. This alows the plug threads to find their way into the head threads and prevents cross threading as almost no torque is involved. You stioll need to worry about the final torque.

 

[beast3300]

I've never had a problem with aluminum heads. I take spark plugs out of engines of all kinds, hot, warm, cold. And install them in all conditions. Especially when diagnosing driveability. I don't think the aluminum is as fragile as some of the websites have you believe.

 

[eljefino]

Yeah the aluminum is fragile, that's why the plug threads are 3/4" long! Look at the plug for a flat head briggs, it's about 3/8.

Most new plugs have a squishy gasket; if you get a feel for this gasket crushing you'll be fine.

 

[Eddie]

Modern heads out of Al are pressure cast and are quite strong, except for ham fisted people who refuse to use care and a torque wrench.

 

[rationull]

Originally Posted By: Boomer
An old trick to avoid cross threading when screwing in a plug...put a length of small ID rubber hose (vacuum line typr) on the end of the plug where the spark plug wire attaches. Now insert the plug into the threaded hole and trun the rubber hose gently. This alows the plug threads to find their way into the head threads and prevents cross threading as almost no torque is involved. You stioll need to worry about the final torque.


That's exactly what I do. I'm having a hard time believing this is really that risky if you're careful and torque to spec. In my case the spec is 18 ft*lbs with antisieze. A beam-type torque wrench should be accurate enough for that kind of thing I'd think.

Are the threads in an aluminum oil pan made of steel or aluminum?

 

[chad8]

Originally Posted By: Astro14
Originally Posted By: bepperb
I think it's more common for the plugs to corrode/weld themselves to the head and cause damage on the way out, than for a person to damage them on the way in.


Amen...very common, the longer they're in the head, the worse the problem. Further, if you use an antisieze compound that lubricates the threads, it's easy to exceed the strength of the threads near recommended torque...


I know i am a jerk for saying this ,but If you need a torque wrench for spark plugs , you shouldn't be changing them .The same goes for lugs. Let the pros at wal-mart do it for u.
The real trick is getting a welded plug out without damaging the head. Heat, pb blaster , and a good impact wrench set real low. knowing when to tighten first and when to loosen is critical.

 

[spasm3]

I always , always change plugs on aluminum heads when they are stone cold. At least 6-8hrs without being driven. I know its controversial but i always use a small amount of anti seize compound. Works for me.

 

[rpn453]

Originally Posted By: Boomer
An old trick to avoid cross threading when screwing in a plug...put a length of small ID rubber hose (vacuum line typr) on the end of the plug where the spark plug wire attaches . . .


Seems unnecessary. I really don't think it's possible for my fingers to cross thread anything but the tiniest of threads, like maybe those ones holding the arms to the frame of eyeglasses. I consider myself a reasonably strong guy, but I'd need a wrench and some significant force to install a spark plug sideways. I also think that having something flexible in between my fingers and the plug would reduce my feel for how it's threading.

Anyway, I've never considered changing plugs to be a risky activity, except when removing ones that have been in for a long time without anti-seize. Those can feel pretty nasty coming out sometimes! I do use a torque wrench and anti-seize, and I check the calibration of the wrench occasionally. Be gentle at all times, thread them in fully with finger strength only, and remember to blow out the holes with compressed air before removing the plugs from the cold (or at least cool) engine.

 

[hattaresguy]

Torque wrench for plugs? Seriously if you work on engines long enough you should develop a feel for the right torque. Spark plugs just need to be tightened until the crush was crushes, which you can feel if you know what your doing.

Lastly the problem isn't aluminum heads, its poor designs, *cough* Ford, or people who leave them in to long. If you look at most manuals they say 100k miles or 5 years. Most people just ignore that 5 year part, which is why they weld themselves in.

Seriously those Ford 5.4's are pretty bad though, a lot of the guys that work for me have them and they are always spitting out plugs. Ford should have recalled all of them.

 

[ltslimjim]

You know, this reminds me, when I changed the plugs on the little Civic a while back, cylinder #4 seemed to feel like it has the makings of being cross-threaded already. It felt like it was over-torqued before. To describe it, I was counting how many complete revoltions I could make the plug turn by hand until it started completely seating, though not snug, and then use no bigger than a 3/8 socket attached to turn it with a general ratcheting motion until it feels like it would need some effort/force to get tighter. At that point, I perform no greater than a 1/2 turn and I'm finished. Not all of my weight, but a small amount of strong arming it for a 1/4-1/2 turn only.

By the way, I do this with the engine cold or having sat for a very long time(8+ hours), at least. I did the same thing for each plug/cylinder and #4 was the only one to 'feel' weird. It wouldn't surprise me if it needs to be worked on eventually, I did apply anti-seize for the first time, FWIW. This may have altered my previous spark plug removal/replacement experiences. I'm still new at it and it wouldn't surprise me if I goofed up somehow. I generally make sure I start them by hand at the right angle so I don't cross-thread them, but I suppose it's possible I may have begun to strip the threads on a previous app. I just don't think I did anything wrong this time, and it felt like a pre-existing condition at cylinder #4, I had put Bosch into the car, but found out later the compatibility issues(especially with the VX) and a mechanic threw in some NGKs for $15, so I said w/e go ahead. So, this was only the 2nd time I've touched the plugs on the Civic. The call for replacement every 30,000 though they may make it longer under some circumstances.

 

[buickman50401]

Originally Posted By: chad8

I know i am a jerk for saying this ,but If you need a torque wrench for spark plugs , you shouldn't be changing them .The same goes for lugs. Let the pros at wal-mart do it for u.

Really? Did you really write that and actually mean it?