daverclasper Posted April 29 Report Share Posted April 29 Hi. I've always just tightened plugs, to a good hand/wrist pressure, using a T bar handled wrench. I've just read some blurb, implying that if a torque wrench is not used, one problem of under torqueing, is that combustion chamber heat may not escape enough through the plugs. Never heard this before?. What do you think?. Cheers, Dave Link to comment Share on other sites More sharing options...
Andrew Posted April 29 Report Share Posted April 29 Just tighten and feel the washer spread and that is enough. The rest is garbage Andrew Link to comment Share on other sites More sharing options...
Unkel Kunkel Posted April 29 Report Share Posted April 29 ‘ I’ve just read some blurb ‘ - can you tell us a bit more regarding this source ? Link to comment Share on other sites More sharing options...
dannyb Posted April 30 Report Share Posted April 30 I would have thought if it was that critical ther would be torque settings in the workshop's manual. Danny Link to comment Share on other sites More sharing options...
Nigel Clark Posted April 30 Report Share Posted April 30 It may be worth using a torque wrench when fitting plugs to alloy cylinder heads, like the Dolomite Sprint, 1850 or TR7, to reduce the risk of stripping threads. But for cast iron heads, as Andrew says, just tighten and feel the washer spread. Nigel 1 Link to comment Share on other sites More sharing options...
Ian Foster Posted April 30 Report Share Posted April 30 GT6 WSM gives 14-16lbft, which is actually quite tight. In my experience it feels quite different when you fit a new plug with an intact crush washer, compared to a plug that is being reused. Ian Link to comment Share on other sites More sharing options...
JohnD Posted April 30 Report Share Posted April 30 14-16 lb-ft is "quite tight"? For a spark plug or for other fasteners? Most specified torques on our cars are twice that, with the infamous crank pulley nut being six times more, and the rear hub nut nearly ten times! Other makes, EG Ford, have hub nuts at 300lb -ft! 'Hand tight' is about 10-12 lbs-ft, in other words tightened without leaning into it, using arm or shoulder muscles. 14-16 is about what you comfortably exert with the arm. I tighten my plugs until they don't go easily, then add about a quarter turn. John Link to comment Share on other sites More sharing options...
micklewis Posted April 30 Report Share Posted April 30 (edited) how tight .? well just torque to it over a coffee .? 3 x dugga duggas ? Most spark plugs (flat seat with gasket type) have a 'crush washer' or gasket which becomes compressed during the initial installation, this allows around half a tightening turn of the plug to be made once contact between cylinder head and gasket has been established. Once the gasket has contacted the cylinder head we would term it is 'finger tight'. Subsequent reuse of the plug will allow only one twelfth of a turn to be made after contact due to the gasket already having been compressed and as a result installation torque being reached much more quickly. Failure to observe this guideline may result in a damaged plug or cylinder head - to the extent of fracture or thread stripping. At best, an overtightened plug will not perform correctly - the spark plug's internal components will be 'stretched' and may not be able to dissipate heat correctly thus effectively increasing the heat range of the plug, making it run hotter and possibly overheat. Plug and engine damage may result.. If using a tapered (conical, without gasket) seat plug type, after contact of the 'shoulder' or mating surfaces of the spark plug and cylinder head is made, only one sixteenth of a turn should be applied. This applies to both new and re-used taper seat type plugs (common in Ford engines). In certain circumstances tapered seat spark plugs can be prone to seizing, this applies especially to certain models of Ford Fiesta and Ka. The best way to guard against problems of this type is to remove plugs midway between recommended service intervals and ensure that any corrosion is cleaned up before replacing. Flat Seat Type (With Gasket) Conical Seat Type Thread diameter 18mm 14mm 12mm 10mm 8mm 18mm 14mm Cast Iron Head 34-45Nm 25-35Nm 15-25Nm 10-15Nm 20-30Nm 15-25Nm 3.5-4.5Kgm 2.5-3.5Kgm 1.5-2.5Kgm 1.0-1.5Kgm 2.0-3.0Kgm 1.5-2.5Kgm 25.3-32.5lbs ft 18.0-25.3lbs ft 10.8-18.0lbs ft 7.2-10.8lbs ft 14.5-21.6lbs ft 10.8-18.0lbs ft Aluminium Head 35-40Nm 25-30Nm 15-20Nm 10-12Nm 8-12Nm 20-30Nm 10-20Nm 3.5-4.0Kgm 2.5-3.0Kgm 1.5-2.0Kgm 1.0-1.2Kgm 0.8-1.0Kgm 2.0-3.0Kgm 1.0-2.0Kgm 25.3-28.9lbs ft 18.0-21.6lbs ft 10.8-14.5lbs ft 7.2-8.7lbs ft 5.8-7.2lbs ft 14.5-21.6lbs ft 7.2-14.5lbs ft Edited April 30 by micklewis coffee 1 Link to comment Share on other sites More sharing options...
Unkel Kunkel Posted April 30 Report Share Posted April 30 Torque wrenches ‘ came into being ‘ to ensure consistent tightening by employees of water company pipe flanges in the US around 1919 , expanding in the late 30 ‘ s with relatively un- skilled workers in mass production of cars extending into war production of things like complex aero engines. The spark plug torque for new , clean dry thread sparking plugs for Triumphs is usually given as 25 ft lbs. Oil or grease can lower this figure by 25 %.dirt rust etc can influence it the other way and a re-used compression washer further confounds any pretense about precision. The correct amount of tightness, like the correct amount of pretty much anything is ‘enough - and no more ‘ but that requires a ‘ feel’ which is is a skill derived from experience. I had the great privilege of knowing a famous watch maker who did the most minute, microscopic work making components from scratch.He also had an wonderful car collection including some enormous veteran cars which he enjoyed working on. I asked him one day how he was able for him to shift from making watches to working on such big heavily- built old cars It was obviously his extraordinary skill, talent and dexterity ( he had enormous hands ,incidentally ) but he very modestly joked, ‘ Oh, just different sized hammers !’ Link to comment Share on other sites More sharing options...
Mjit Posted April 30 Report Share Posted April 30 (edited) Here's a YouTube video all about tightening NGK spark plug, posted by a company called Niterra...who used to be known as NGK Spark Plug Co. so might just know what they are talking about! Edited April 30 by Mjit Link to comment Share on other sites More sharing options...
micklewis Posted April 30 Report Share Posted April 30 1 minute ago, Mjit said: Here's a YouTube video all about tightening NGK spark plug, posted by a company called Niterra...who used to be known as NGK Spark Plug Co. so might just know what they are talking about! this is for modern alloy heads , ,figures as per my chart differenciate the difference between cast iron and alloy heads , mick Link to comment Share on other sites More sharing options...
bob_9447 Posted May 1 Report Share Posted May 1 Just screw in by hand until the Plug hits the head (cylinder head!), then a further quarter turn. That used to be the manufacturers instructions in the 60s and 70s. Link to comment Share on other sites More sharing options...
Mjit Posted May 1 Report Share Posted May 1 3 hours ago, bob_9447 said: Just screw in by hand until the Plug hits the head (cylinder head!), then a further quarter turn. That used to be the manufacturers instructions in the 60s and 70s. Which isn't much different to what the NKG video has for one of our spek plugs - "B*" plugs are 14mm so finger tight then 1/2 to 2/3 turn for a brand new plug (new crush washer) or 1/12 turn if refitting an existing one (pre-crushed crush washer). And @micklewis while you're chart does have different torques for iron/alloy heads for our plugs that 34-45Nm vs. 35-40Nm - so assuming you're aiming for the middle of the range basically the same. Link to comment Share on other sites More sharing options...
Piglet Posted May 1 Report Share Posted May 1 Torque wrench?? No no no. As mentioned do them up by hand then nip them up with a little turn of the ratchet. Alex Link to comment Share on other sites More sharing options...
Chris A Posted May 2 Report Share Posted May 2 22 hours ago, bob_9447 said: Just screw in by hand until the Plug hits the head (cylinder head!), then a further quarter turn. That used to be the manufacturers instructions in the 60s and 70s. That's what I was 'taught', or rather it was the common practice amongst us youngsters back then Link to comment Share on other sites More sharing options...
Mjit Posted May 2 Report Share Posted May 2 (edited) They should be torqued, and specifically to 20 lbf. ft. ...At least that's what it says on page 06.1 of the Triumph Spitfire IV Repair Operations Manual, 3rd edition! (though I wonder if anyone has ever done that) I think the "hand tight + quater turn" is what's usually printed on the spark plug box isn't it? Edited May 2 by Mjit Link to comment Share on other sites More sharing options...
PeteH Posted May 3 Report Share Posted May 3 (edited) In something like 60 years now. I don`t think I have ever used a torque wrench on a Spark Plug, Clean the thread, maybe a lick of Graphite? screw to finger tight, and a light "nip". Cannot remember ever having a Failure? or at least not one atributable?. I use torgue wrenches for other stuff. And always for wheel nut/bolts. Having experienced a wheel losing 3 of 5 due to Threads being taken beyond their elastic limit. Tyre fitters with "windy guns" are a ******* menace. P.s. Sailed with and Old Chief Engineer, who`s favourite quote, was " If at first you don`t succeed, get a bigger Hammer!". 😁 Pete Edited May 3 by PeteH Link to comment Share on other sites More sharing options...
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