Sparkplug overtightened.

[shDK]

hi all.

i changed my spark plugs yesterday. and apparently i missread the torque scale provided by NGK.

i tightened them 25 nm(correct for plugs with a crush gasket) but since they are with tapered conical seat they should only be tightened 20 nm. today i unscreewed them and tightened them to correct 20 nm. the threads where fine.

my question is. is there a chance i have damaged the conical seat in the alluminium cyllinderhead? the engine runs fine. i think i will try to controltighten them 20 nm again in a few days to see if they come loose.

but what do you guys think? have i damaged the sparkplug seat in the cyllinderhead?

søren

 

[Fleetmon]

I really can't see how....you're only talking about 5 ft lbs difference

 

[147_Grain]

Highly doubt there is an issue.

 

[Trav]

Don't bother loosening and re tightening 5nm is only a couple of ftlb and well within the threads "normal range".
You are probably causing more wear to the threads and seat repeatedly disturbing them.

 

[bigt61]

Torque spark plugs? I've changed them for 40 years and never done that, including 3 to 4 times a weekend in 20+ years of racing. Just put them in snug and let them eat.

 

[supton]

I'm guessing it really starts to matter after 5 years / 100kmiles. 20newton-meters vs 25newton-meters, minor; hand tight vs "good 'n' tight" though likely does at high miles/age.

 

[shDK]

its not as much the treads i'm worried about. as it is the spark plug seat in the soft alluminium cyllinderhead. i can understand that the tappered seat sparkplug are more fragile then those with crush seals.

but thanks for your replyes

 

[Falken]

You're fine.

 

[Trav]

Originally Posted By: shDK
its not as much the treads i'm worried about. as it is the spark plug seat in the soft alluminium cyllinderhead. i can understand that the tappered seat sparkplug are more fragile then those with crush seals.

but thanks for your replyes



3.6 ftlb is not going to damage the seat one way or the other. You could over tighten them until you strip the threads and still probably not damage the seat itself.

 

[zzyzzx]

Originally Posted By: Trav
Don't bother loosening and re tightening 5nm is only a couple of ftlb and well within the threads "normal range".
You are probably causing more wear to the threads and seat repeatedly disturbing them.


Exactly what I was thinking.

 

[shDK]

yeah.. but i allready did loose and retighten them today at work. i coult screw them out by fingers so the treads are fine and without damage. was mostly the conical plug seat i was worried about.

 

[mount]

They're fine. But even if they weren't, what would you be able to do about it anyway? lol. Let 'er buck.

I would've left them in there instead of retorquing. Once they're tightened, if any damage was done, you're only going to make it worse. Same goes for any other bolt I tighten. I was tightening a bolt into aluminum on my Passat the other day, and I'm fairly sure it started to rip the threads out as I came to a stop. Wasn't going to back it out and find out though!

If by some chance it needs to be changed again, we'll deal with it then. I'll likely smoke a deer with it next week anyway making all this pointless.

 

[shDK]

I already took them out and retighten them to correct spec today. They seal perfekt and felt good and firm when tightening them. I am not planing to tighting them any further but just check if they will become loose.

 

[RF Overlord]

shDK, you are WAY over-thinking this. Relax and have a Tuborg.

 

[shDK]

Originally Posted By: RF Overlord
shDK, you are WAY over-thinking this. Relax and have a Tuborg.


i will.. actually i am having one rigt now. Can you buy tuborg in the US ?

 

[spackard]

spark plug is 14mm x 1.25 This means 14 mm outside
diameter and 1.25 mm from the crest of one thread to the crest of the next.
By converting 1.25 mm to inches you get .04921875. Which is how far the plug will move in one revolution. Dividing this into 1 inch you get 20.31746032 threads per inch.

So, 3.6lb-ft * ~20 TPI = 72lb-ft on the first thread.

 

[Trav]

Oh brother. Talk about over thinking things. So here is the big question..
How much is the first thread rated for max?

As long as your doing the math its 3.6878107463850003 Lb-Ft.

 

[TFB1]

Originally Posted By: spackard
So, 3.6lb-ft * ~20 TPI = 72lb-ft on the first thread.


But that'd only be true if there were no other threads to didtribute the load... Try holding a several hundred pound load by a bolt with only one thread and see how long it stays in place...

BTW there is no load on any of the threads untill the plug starts to tighten...


I'm with the guy who stated he's never used a torque wrench on a spark plug and I've owned vehicles since 1966..

 

[Trav]

Originally Posted By: TFB1
Originally Posted By: spackard
So, 3.6lb-ft * ~20 TPI = 72lb-ft on the first thread.


But that'd only be true if there were no other threads to didtribute the load... Try holding a several hundred pound load by a bolt with only one thread and see how long it stays in place...

BTW there is no load on any of the threads untill the plug starts to tighten...


I'm with the guy who stated he's never used a torque wrench on a spark plug and I've owned vehicles since 1966..


Maybe this is the same guy who worked for Ford and figured out Ford could get away with 3 threads on the plugs.