Author Topic: Spark plug changing information  (Read 1128 times)

Droneranger

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Spark plug changing information
« on: June 11, 2021, 12:51:35 PM »
Here is some information from NGK on changing spark plugs that should correct some advice given in earlier posts.


culzean

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Re: Spark plug changing information
« Reply #1 on: June 11, 2021, 01:19:14 PM »
Here is some information from NGK on changing spark plugs that should correct some advice given in earlier posts.

Never used a torque wrench on any spark plug ( or anything else except important things like big end bolts or cylinder head bolts where you need to actually stretch the bolt a fairly accurate amount when tightening it 'preload' ).  For normal car sized spark plugs the 'hand tight and then 1/2 turn' for a fresh crush washer and '1/8 turn for a used washer' ( if you are refitting a used plug) is all I do.  Used to use a light smear of copper grease on the older passivated zinc plated non-iridium plugs because they could give problems with  seizing up,  but with long life plugs they have a tri-valent coating that is specially designed not to stick in aluminium heads, so haven't bothered with lube for last 10 years+.

Torque values are always for a dry thread. 
« Last Edit: June 11, 2021, 02:56:51 PM by culzean »
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culzean

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Re: Spark plug changing information
« Reply #2 on: June 11, 2021, 05:41:07 PM »
Hand tight is using either the box spanner or socket extension with no tommy bar or ratchet handle in place, just snug the spark plug down by finger pressure - you only want to get the crush washer touching the cylinder head - then fit the tommy bar or attach the ratchet drive and move it 180degrees.  Do you have you calibration checked on torque wrenches every year, are they quality maker.  A cheap or uncalibrated torque wrench can be very misleading. Do you always screw the wrench below the required torque and then take it up to required torque,  Do you store torque wrench with spring slackened off ?

Off spark plugs for a second -  the motor industry generally, and engine builders in particular use automatic torque+ angle to ensure correct tightening.  This means a small torque to make fastener face contact the seating  ( pretty much equivalent of 'hand tight' ) and then rotate the fastener through a known angle,  this is way more accurate than a torque wrench on its own.  All a torque wrench is measuring is friction between the threads, and once the faces are together it measures friction between the face of the fastener and its seat. Many fasteners in motor industry in engines do get lubricated with a specified lubricant before tightening, any deviation from lubricant affects friction which affects torque.  I rather use threadlock on brake fasteners than torque wrenches.

I worked for a supplier of assemblies to many car companies and we used the low torque + angle method on fasteners, many of them were automatic electrical powered devices that would lock out the assembly cell if correct angle was not achieved.

https://www.enginerepairshop.com/torque-specifications.html
« Last Edit: June 11, 2021, 05:56:20 PM by culzean »
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Westy36

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Re: Spark plug changing information
« Reply #3 on: June 11, 2021, 09:32:20 PM »
Copper slip on threads is bonkers. Good post!  :D Good point re cold engine too. Well worth remembering, although in winter it's tempting to change the plugs when the engine is warm so your hands don't freeze!

Fair point about how tight is hand tight? For me it has been down to servicing my own motors for 30yrs and experience. Touch wood never had a problem, but first turn of the key post plug renewal always comes with a little mild apprehension! Torque wrench is safest for sure though.

Wheel nuts. F. tight is how tight.  ;D ;D Hard to over tighten yourself I would imagine. For sure, wheel places with their air guns can be over zealous, but I doubt anyone would over tighten their own nuts.

What is worth remembering, is to check they are tight again after several miles.
« Last Edit: June 11, 2021, 09:35:01 PM by Westy36 »

fashionphotography

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Re: Spark plug changing information
« Reply #4 on: August 05, 2021, 06:12:48 PM »
the reason why garage mechanics put copperslip on threads and have done for many years is it prevents them from seizing up... simple...

culzean

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Re: Spark plug changing information
« Reply #5 on: August 05, 2021, 07:00:28 PM »
the reason why garage mechanics put copperslip on threads and have done for many years is it prevents them from seizing up... simple...

Plugs usually difficult to get out if they have been left in too long, like the rear 4 plugs om MK1 Jazz, which are ignored by dealers and independent garages.  The iridium / platinum long life plugs have a special thread coating ( because they are designed to stay in engine 70,000 miles + ) that does not bond with aluminium of head.   I did use the lightest smear of copper grease on 'normal life plugs' having had fun removing some in the past ( fitted by others ) - some I had to do a small turn out and then a small turn back in because they were that tight ( and the steel wall where thread joins hexagon is surprisingly thin ) - with liberal applications of penetrating oil and wait for it to get to work before daring to try to unscrew any more, copper grease does help, but not needed on modern plugs ( or plugs that are changed regularly )..
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

fashionphotography

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Re: Spark plug changing information
« Reply #6 on: August 05, 2021, 08:05:37 PM »
the reason why garage mechanics put copperslip on threads and have done for many years is it prevents them from seizing up... simple...



very true.. not everyone goes for the long life plugs though..
there seams to be a myth going round about not using copperslip on plug threads ?
anyway nothings as much fun as trying to get the plugs out of the Ford Kent engines such as the KA.
times i had to try and weld an old cylinder head bolt into what left stuck in the head  to get them extracted..

Plugs usually difficult to get out if they have been left in too long, like the rear 4 plugs om MK1 Jazz, which are ignored by dealers and independent garages.  The iridium / platinum long life plugs have a special thread coating ( because they are designed to stay in engine 70,000 miles + ) that does not bond with aluminium of head.   I did use the lightest smear of copper grease on 'normal life plugs' having had fun removing some in the past ( fitted by others ) - some I had to do a small turn out and then a small turn back in because they were that tight ( and the steel wall where thread joins hexagon is surprisingly thin ) - with liberal applications of penetrating oil and wait for it to get to work before daring to try to unscrew any more, copper grease does help, but not needed on modern plugs ( or plugs that are changed regularly )..

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