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CCKW Spark Plugs - Suggest Torque Wrench Setting ?


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Guys, your wise counsel please.


Changed the spark plugs on the CCKW today as part of the comprehensive service I'm on with to try and baseline the condition of the vehicle and to get to understand it.


The gap on the old ones was old ones was about 50% too large, and they were pretty black, although the latter is to be expected given the short runs I've been doing.




The manual says says to tighten the plug until it bottoms then turn another 1/4 to 1/2 turn until firm.


For consistency I'd prefer to use a torque wrench. I'm thinking of a lowish setting, perhaps 15 lb. Your thoughts/opinions would be appreciated on the setting to use.


Kind regards to all



Edited by Vulture
Correct spelling mistake, and add photo.
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The main reason spark plug torque has become an issue is due to aluminum heads. In an old cast iron GMC 270 ripping the thread out is really not an issue (ok, but you really, really have to want to do it). But in an aluminum head its a very real issue.


Since the plugs are grounded by the treads you really only need to make sure they are clean for a good electrical path.


Make sure you use the crush washer and 1/4 - 1/2 turn past seated in good enough. If you must use a torque wrench 20ft lbs is a good target number.

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Most of the plug makers state keep oil / grease off because the heat carbons it up, in fact they state they are factory coated with a few microns of whatever and that is all that is needed.

In the case of difficult alloy heads - then I tend to use a slight smear of Moly Paul PCB.



Other than taper plugs , makers (who have done the tests) state the heat transfer is in the main across the gasket crush washer to the head - and you can adversly affect the heat transfer (& thus the plug heat range) by over crushing the washer. This may be the case with high performance alloy heads but with a CI head - I doubt if it is so important.


Modern alloy heads with plugs well sunk - best to have a bit rake around with a small pry and air line blow out before removal. To stop cross threading , use a extension from a bit of reinforced air line about 6" long to screw the plug home whilst counting the turns. If it does not go easy then probably there is heat distortion on the thread. Rather than use a plug hole cleaning tap , this is when it is best to use a bit of PCB and use the plug as a roll form.


No need for a torque-wrench , often access is bad to use correct , 1/2 turn for a new crush washer , 1/4 turn for a used one. taper seat plugs - follow the makers instructions for the angle..

Edited by ruxy
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Spin them in by hand then nip them up no more than half a turn with a nomal 1/2 in tommy bar made into a tee. Too tight might present difficulty next time you want to get them out, and unless they are flapping about a little loose is fine (watch for bubbles round the washer when its running).


As it happens an engine like yours will run for years with the plugs in hand tight, but follow the book and you can do no wrong. I see far more problems due to over enthusiastic tightening (although even then the monkey metal that plugs are made from is no match for decent Bethlehem cast iron!)


Just firm with a T bar is perfect.

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Oh and Champion J8Cs or AC 44 (or 45s if you need something a little hotter for burning that excess oil that short runs result in) are better plugs.....


My admittedly limited experience has been the opposite - mainly because Champion J8Cs oiled up quickly, whereas NGK ran hotter and stayed a lot cleaner :-D. Is there any particular reason why you do not rate the NGKs, Paul?

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I do rate them but this happened last week with a flathead V8 I was doing that had NGKs in rather than N10s. I could not work out why it kept misfiring even though it was set up by the book (or so I thought)


The answer was that the electrodes on the NGK were longer than they should have been and the valves were actually tapping the gaps down to about 8 thou! You can just see the witness mark on the edge of the valve in this pic.


Mind you they may have been counterfeit plugs as the market is flooded with them, so no offence to NGK. But dont blame me if I dont use them when I can find the original specified make and number!


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Thank you for your thoughts, this has been an informative thread. The overwhelming consensus appears to be not to over-engineer the activity on such a basic engine ! LOL :n00b: :nut:


Must confess I have already applied a dab of high temp grease to each plug. On the basis of what I’ ve read here I probably won’t do that again :red:


The debate over what plugs to use is very interesting. I picked up my NGKs from Rex Ward. Paul, I never appreciated that counterfeit parts were such a problem ! :wow: Good pic btw.


Kind regards to all, on this depressing overcast autumn day here in the UK. (How I wish it was summer, so much to do, and so little time available)



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I find it amazing that anyone should bother to make counterfeit plugs - they're not exactly high value items although I guess the volume sold is big. I get mine from a major auto elec parts supplier - sounds like it's best not to trust back street shops or the high street market then.

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If there is a market there are knock-offs.....


We had a knock-off generator when I worked in Iraq - with a CV12 engine in it! When we contacted Perkins (we were having trouble) we gave them the serial number and they said mmmmmm...............not one of ours guv..


If an engine runs well with dodgy plugs, grand. But whether its rotor arms, condensers, leads or plugs or anything else for that matter sometimes the quality just aint what it used to be, and if your engine is misbehaving then dont assume all is well just because you put new bits on it.

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