12 Nm on the plugs? thats not very tight

beaver

beaver

Well-known member
UKGSer Subscriber
Joined
Oct 8, 2017
Messages
1,841
Reaction score
2
Location
Bradford
Have just replaced the plugs in my LC.. the dealer sold me 4 of them so I could do the full set :mad:

So, I put them down to 12 Nm and it didn't feel tight enough to me.. so backed off again, and did it again, and this time it went further... so at the initial 12 Nm its not fully crushing the sealing washer.. My thoughts are this could crush under use and the plug could become lose?.. Also, the ones I took out (BMW service) were not at 12Nm... they were quite a bit tighter.

So, they are now in at 15 Nm and the washer appears crushed and no where to go... Anyone else think this?
 
Hi

The 12Nm is the factory figure, I think the old air-cooled was 23Nm, so as you say rather lower.

Although in fairness, I don't think I've ever used a torque wrench on a spark plug.
 
Steptoe said:
Same here, i've managed for more than 40 years replacing them in cars bikes and airplanes.
Click to expand...

My guess is that at the first attempt the soft washer got compressed (as is meant to be). Second time it felt different because now you have an already compressed washer.


If I may suggest, try stopping at the prescribed torque and see what happens. It is my humble prediction that 12Nm might be enough. And for next set of plugs, try not to redo it. The washer works best if torqued only once. (washer goes from soft to hard when compressed).
 
knutk said:
My guess is that at the first attempt the soft washer got compressed (as is meant to be). Second time it felt different because now you have an already compressed washer.


If I may suggest, try stopping at the prescribed torque and see what happens. It is my humble prediction that 12Nm might be enough. And for next set of plugs, try not to redo it. The washer works best if torqued only once. (washer goes from soft to hard when compressed).
Click to expand...

Well the plugs on my classic bikes have been in and out more times than a dick in a brothel and I've never torqued the plugs, washers are the same ones and are still fine. Screw in 'till stop then tighten 1/8 turn. all done.

Torquing is becoming anal. I agree, big end bolts, cylinder heads, crankshaft nuts etc.,should be torqued but now it's "what torque for my wing mirrors, mudguard bolts etc" FFS if it feels tight it is tight.

BMW have torque figures for all the parts because the assembly tools are all set this way for speed of manufacture. Socket on - zip - socket off, no human thought whatsoever.
 
iandavid said:
Well the plugs on my classic bikes have been in and out more times than a dick in a brothel and I've never torqued the plugs, washers are the same ones and are still fine. Screw in 'till stop then tighten 1/8 turn. all done.

Torquing is becoming anal. I agree, big end bolts, cylinder heads, crankshaft nuts etc.,should be torqued but now it's "what torque for my wing mirrors, mudguard bolts etc" FFS if it feels tight it is tight.

BMW have torque figures for all the parts because the assembly tools are all set this way for speed of manufacture. Socket on - zip - socket off, no human thought whatsoever.
Click to expand...

Bravo Sir and well said :clap
 
Not forgetting that torque settings are dry, unless otherwise specified.

Sae have torque guide for diameter/material, always worth checking.

Assuming you know what it's made out of, the diameter and the pitch.

Otherwise do up fucking tight, then a smidgen more for luck.

Sent from my SM-G925F using Tapatalk
 
Engineer said:
Was one of those planes the one you crashed in? ;)
Click to expand...

Two pilot error = both crashed, hard impact. Tri-Pacer and EP9
One oil pressure lost, emergency landing in a field with body damage. Islander.
All in the UK

All my work was on twin beeches, Twin otter and DC3, in USA. :D
 
knutk said:
My guess is that at the first attempt the soft washer got compressed (as is meant to be). Second time it felt different because now you have an already compressed washer.


If I may suggest, try stopping at the prescribed torque and see what happens. It is my humble prediction that 12Nm might be enough. And for next set of plugs, try not to redo it. The washer works best if torqued only once. (washer goes from soft to hard when compressed).
Click to expand...

What.. maybe I didn't make it clear enough.. I took it out and looked, and the washed was still not compressed fully..... thats why I didn't like the feel of it?.. thats why it went more the second time as the washer compressed even more... are you saying plugs can only be used once?... I've had loads of plugs thats been in and out countless times. As others say, I've always done it by feel.. but thats more than 12Nm for sure to get it fully comressed. just thinking if it's not fully compressed, does it seal right... or can it come lose as it compresses / relaxes over time?.... I had the Torque wrench out so thought I'd do it to the book... but will revert to plan 'A' in future... turn until it stops, then a nip more... let's face it, the thread is about 1" long so would be hard to strip... :)
 
As long as we are talking about torqueing a steel bolt into steel threads, just about right will do.
Bolts into ligt alloys is a totaly different ball game.

Light alloys accumulates loads, thus even over torquing once will do permanent damage. Even if you don't notice it right away, whoever works on the bike some time in the future eventually will learn it the hard way.
As for reusing soft washers, same thing.
Second time in use it needs a higher torque to seal properly. Again, if steel into steel, no big deal. But steel into light alloys, all I can say is: Gentlemen, you are peeing in yor pants to stay warm..
 
mrtee43 said:
I must be missing something here. 4 plugs on an LC ?
Click to expand...

Yes.. didn't you know they had 4 plugs?.. My old Twin Cam had 4 plugs so sounded good to me :) and obviously the spares dept Allan Jefferies know they take 4 ;)
 
beaver said:
Yes.. didn't you know they had 4 plugs?.. My old Twin Cam had 4 plugs so sounded good to me :) and obviously the spares dept Allan Jefferies know they take 4 ;)
Click to expand...

I needed four candles for mine.. right fuckin palaver ensued...
 
beaver said:
... are you saying plugs can only be used once?... I've had loads of plugs thats been in and out countless times. As others say, I've always done it by feel.. but thats more than 12Nm for sure to get it fully comressed. just thinking if it's not fully compressed, does it seal right... or can it come lose as it compresses / relaxes over time?.... I had the Torque wrench out so thought I'd do it to the book... but will revert to plan 'A' in future... turn until it stops, then a nip more... let's face it, the thread is about 1" long so would be hard to strip... :)
Click to expand...


In a perfect world, the washer should be used only once, this goes for any soft washer (aluminum as well as copper). I know… we have all reused washer at some time or other. But second time around the plug needs to be torqued harder to avoid leaks.

As for sparkplugs, for the last 20 years my engines have not needed to remove the sparkplugs except for when change is due. I have always torqued them, and never had a problem by the plugs coming loose. Again, if the head has steel inserts for the sparkplugs, the torque is not critical, but if the sparkplugs are screwed into the alloy and the pugs are over torqued, sooner or later there will be a problem. Does the LC heads have steel inserts? Frankly, I have never checked, so I couldn't say...
 
knutk said:
In a perfect world, the washer should be used only once, this goes for any soft washer (aluminum as well as copper). I know… we have all reused washer at some time or other. But second time around the plug needs to be torqued harder to avoid leaks.

As for sparkplugs, for the last 20 years my engines have not needed to remove the sparkplugs except for when change is due. I have always torqued them, and never had a problem by the plugs coming loose. Again, if the head has steel inserts for the sparkplugs, the torque is not critical, but if the sparkplugs are screwed into the alloy and the pugs are over torqued, sooner or later there will be a problem. Does the LC heads have steel inserts? Frankly, I have never checked, so I couldn't say...
Click to expand...

maybe you want to try put a new plug in at 12 Nm.. then try torque it again and it turnes another 1/4 of a turn... are you saying this is correct?... I don't think so... the washer is still giving away under the pressure. if you keep on doing it, it will reach a point where it will not move again... but its very border line if you ask me.. 14-15 Nm solves the issue ;)
 
beaver said:
maybe you want to try put a new plug in at 12 Nm.. then try torque it again and it turnes another 1/4 of a turn... are you saying this is correct?... I don't think so... the washer is still giving away under the pressure. if you keep on doing it, it will reach a point where it will not move again... but its very border line if you ask me.. 14-15 Nm solves the issue ;)
Click to expand...

Frankly, I have never checked, so I couldn't say.

What I do know is that both aluminum and copper washers are softened, and once they have been exposed to pressure they will become harder. I have reused washers in cases where new ones where not available, but generally I use them only once (they cost next to nothing) and have not bothered to check how much they compress.
I put in a new washer, torque the screw to prescribed value and leave it alone. So far this way of doing it has never caused any problems.
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
You must log in or register to reply here.


Back
Top Bottom