Spark Plug Replacement

[ribaree]

Hi,
Anyone know the torque setting for spark plugs ?

Cheers

[Scaredycrow]

"tight but not too tight"

[bd581]

DON'T DO THAT!!!!!!!!!!!!!!!!
Bad idea.

The actual number is 18NM. Which is absolutely bugger all. Not much more than finger tight.

Over tigtening (which taking it 5mm-1cm further than the point where you just feel it go tight is) will result in the plug gap opening. The thread will stretch which pulls the side electrode and alters the gap.
If you have seen a head crack, its not because of overtightning of the plug, just a co-incidence.
You'll break the plug off inside the head way before that will happen.
Just ask any old mechanic about champion spak plugs, they were notorious for breaking off in the head

[Scaredycrow]

DON'T DO THAT!!!!!!!!!!!!!!!!
Bad idea.

The actual number is 18NM. Which is absolutely bugger all. Not much more than finger tight.

Over tigtening (which taking it 5mm-1cm further than the point where you just feel it go tight is) will result in the plug gap opening. The thread will stretch which pulls the side electrode and alters the gap.
If you have seen a head crack, its not because of overtightning of the plug, just a co-incidence.
You'll break the plug off inside the head way before that will happen.
Just ask any old mechanic about champion spak plugs, they were notorious for breaking off in the head

Agreed. I'm curious where you got the 18NM number from? Share some doco?

[Doug_MPS6]

Agreed with BD581. Specifying a turn "distance" on a wrench is not much help. It depends on the length of the lever - and that also determines the torque applied. Dangerous territory. Plug torques are usually low, around 15-20ft.lb, just a nip up. See Spark Plug Installation Instructions

BTW, I discovered (from Melville Mazda) that the MPS6 plugs are only replaced at 100,000kms. I assume this to be the real gen but would like confirmation.

[bd581]

Number came from just the first workshop manual i picked up out of the cupboard. Holden Rodeo V6.

That number won't vary a whole lot between cars. Point is, you don't tighten them much.

You can cause all sorts of problems overtightning plugs.

Just "nip" them up. Don't ever use a large wratchet to tighten them. 3/8 drive at the most

[Duk]

Tighten it with a rachet applying a consistant force, once you hit the normal seated position, you wont be able to turn the plug anymore if you dont exert any more force.. Its just feel , im a bit biased because i work in the industry.... That being said, the sparkies i change everyday have crush washers on them, and you can feel the washer bite and crush, and thats it.. For the denso replacements i got for the mps, they had no washer, soo it was just tighten until you feel it bite, and give it a little nip. done...

[Doug_MPS6]

DUK, specs for washered and unwashered conical seating plugs are different and can be found on a variety of websites, including the one I listed above. Best way to tighten them up is to use an accurate torque wrench if possible but often access can be difficult. Avoiding a full-fisted grip and using one or two fingers is a good way to avoid over-tightening too.

[lup15]

workshop manual says 10-14nm

[projectrracing]

workshop manual says 10-14nm

that is low. i'm surprised the plug don't shoot out with combustion happening underneth them.

[andy b]

the MPS6 plugs are only replaced at 100,000kms. I assume this to be the real gen but would like confirmation.

I thought it was every 70,000km as per service schedule?

[rd415]

MPS6 Manual has tightening Torque of 10 to 24 nm

Tightening torque 10-14 N·m - this spec was cut and pasted straight out of MPS3 manual

Conclusion - THEY AIN'T TIGHT

I used to demo to students in 3rd year the effects of even slightly overtightening spark plugs on an oscilloscope, (part of training to read oscilloscopes) quite amazing the variation in spark line with different students tightening carefully gapped spark plugs. Around 5kv difference in the spark lines is normal overtightened plugs only slightly it's much higher.

For the layman the spark line is a series of lines (one for each cylinder) on the oscilloscope that shows the voltage required to jump the plug gap. It is almost impossible to get exactly the same KV on each plug

[bd581]

Can somebody explain whe the post describing the incorrect way to tighten spark plugs was deleted making a lot of the comments made make very little sence for people using this information it the future?