"torque angle" vs. torque wrench comparison

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Hi all:
A few weeks back, all of you were very helpful with tips on spark plug replacement for my 95 Maxima. The job went very well and all 6 plugs are now replaced.

Now to the question... NGK says that in lieu of a torque wrench, the "torque angle" method can be used. For the plug I used, they say 1/2 to 2/3 of a turn will produce their recommended torque of 18-21.6 lb ft of torque. My factory service manual calls for 14-22 lb ft of torque so I decided 18 lb ft would be a good midpoint selection for torque. For this job, because I didn't want to take any chances with my aluminum heads and needed one anyway, I bought a new Precision Tools split beam 8-50 lb ft torque wrench. They are apparently one of the best manufacturers out there - building them from scratch in the USA since 1938!

Since I'm a naturally curious person, I wanted to compare the amount of turn at the point I reached 18 lb ft. It wasn't very straightforward because of obstructions in the engine bay I had to remount the torque wrench/extension-socket upwards of 3-4 times so some of the summations I reached for the rear three plugs probably aren't exact - for instance 3 approximately 1/4 turns plus a bit more. But for the front three, I was able to reach 18 lb ft in one continuous arc. During the turn(s) I was careful to keep the long extension centered in the spark plug hole with my fingers of my left hand so as not to crack the insulator and being mindful not to apply any counter-torque - just keep it centered. I noted that to reach 18 lb ft, it took about 270 to 300 degrees of turn compared to NGK's "torque angle" value of 180 to 240 degrees of turn. And, what makes it even more interesting is if the NGK torque angle method produces between 18 and 21.6 lb ft of torque, one would presume that 18 would be reached at the 180 degree mark, and 21.6 reached at 240 degrees, and I was 270+ for 18 on the torque wrench. Note no antiseize or crow feet extenders were used which would have altered things

I asked NGK, and like I suspected, they said to basically defer to the torque wrench as long as I was confident it was calibrated properly which I would have no reason to doubt as it was brand new. But I'm still left mystified as to how they can tell folks they can rely on their torque angle method when, at least in my case, it didn't seem to jive at all.

Has anyone done a similar experiment? Thoughts on my observations?
 
It's not surprising that it took more torque to get the same amount of bolt tension as angle torque. You're putting plugs in a 25 year old car! There's no way the threads are in the same condition as when the car was new. You would have to remove the head, thoroughly clean the threads with a brush wheel and solvent, then run a tap through them--and then, you'd be able to do an adequate comparison. The reason for the delta between the torque wrench and angle torque is almost certainly related to the fact that the threads have more friction than when new.

Keep in mind, torque values are just a proxy for bolt tension. What really matters is the bolt tension, and for that angle torque is almost always more precise.
 
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Practice tightening and measuring fasteners' torque. You'll get a pretty good idea of what # lbs of torque feels like. I never try to use a torque wrench on a (semi-modern, cramped) V engine, just not worth the bother, too convoluted trying to get in there with extensions and swivels, torque wrench way too long, etc.

I'm sure someone will say the sky is falling if I don't, but I'm pretty good at estimating the torque a fastener needs up to ~100 ft lbs.
 
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Originally Posted by JOD
NissanMaxima said:
Hi all:
Keep in mind, torque values are just a proxy for bolt tension. What really matters is the bolt tension, and for that angle torque is almost always more precise.


THIS - SO MUCH THIS....
 
Are you positive you had the plugs fully turned down until the crush washer was touching before you started torquing? That's the only reason I can think of your discrepancy. My plugs are the non-gasket taper seat type, so I cannot attempt to duplicate your trial.

Thanks for sharing.
 
Originally Posted by tundraotto
Originally Posted by JOD
NissanMaxima said:
Hi all:
Keep in mind, torque values are just a proxy for bolt tension. What really matters is the bolt tension, and for that angle torque is almost always more precise.


THIS - SO MUCH THIS....


Yes, yes. Turn angle is much more consistent than torque.
 
Thanks all. I had not thought of thread condition as a factor here. But if there is essentially some "counter torque" from the thread condition, wouldn't my 18 lb ft be achieved sooner in terms of the amount of rotation ultimately observed? Just like anti-seize would delay the rotation point where any set torque value would be achieved and hence their recommendation to reduce torque by 20% if using anti-seize.

But in any case, what about having torqued to a rotation point of 3/4 to 7/8 of a turn compared to their maximum torque angle of 2/3 of a turn? I even attempted a calculation based on thread pitch and if I'm right, the additional rotation even up to 7/8 of a turn past finger tight would insert them to about 0.26 mm deeper than at 2/3 turn. That's only ten thousands of an inch. I would think there would be enough crush potential in the crush washer gasket to accommodate this.

As for being full turned down, yes. After the first one, I first inserted the socket and extension alone to check finger tight as I had used the rubber hose trick to get them in finger tight. Good point though!
 
Originally Posted by NissanMaxima
Thanks all. I had not thought of thread condition as a factor here. But if there is essentially some "counter torque" from the thread condition, wouldn't my 18 lb ft be achieved sooner in terms of the amount of rotation ultimately observed? Just like anti-seize would delay the rotation point where any set torque value would be achieved and hence their recommendation to reduce torque by 20% if using anti-seize.



Not necessarily. Thread deformation is what's going to alter the reading. Cleaning and running a tap through will help, do a degree. Basically, the threaded part has the potential to become "looser".

There's enough margin in most spark plug assemblies that I don't think it's a huge deal either way, but this is likely why you experienced what you did--and why I much prefer angle torque when suitable.
 
Originally Posted by A_Harman
Originally Posted by tundraotto
Originally Posted by JOD
NissanMaxima said:
Hi all:
Keep in mind, torque values are just a proxy for bolt tension. What really matters is the bolt tension, and for that angle torque is almost always more precise.


THIS - SO MUCH THIS....


Yes, yes. Turn angle is much more consistent than torque.



But how specs will list and publish angle? Compared to torque specs?
 
@user52165:
This is why I followed the torque spec in my 400+ page factory service manual. It said nothing about angle torque and the section was under Maintenance so was clearly intended to instruct for replacing spark plugs at the service interval. I noticed the torque angle was somewhat beyond 2/3 turn but continued to use 18 lb ft on the rest of the plugs putting my faith in my official Nissan FSM and also putting my faith in the fact I had chosen the midpoint of Nissan's maintenance torque specs of 14-22 lb ft.
 
"torque angle" procedure is often a 2 step process:

1. Torque to a low torque value specified by the manufacturer
2. Turn fastener through the angle specified by the manufacturer.
 
Originally Posted by SubLGT
"torque angle" procedure is often a 2 step process:

1. Torque to a low torque value specified by the manufacturer
2. Turn fastener through the angle specified by the manufacturer.


Right. Torque angles are a torque followed by an angle. If anyone can link me to an FSM that specifies only an angle, I want to see it.
 
Originally Posted by SubLGT
"torque angle" procedure is often a 2 step process:

1. Torque to a low torque value specified by the manufacturer
2. Turn fastener through the angle specified by the manufacturer.


Correct, I also have never seen an angle given with no initial torque being set. So even angle specs depend on a standard torque wrench for initial accuracy.
From what I have seen this is usually for stretch bolts or nuts with some sort of hindrance eg nyloc, jet nuts or distorted thread nut, some of these are commonly found on hubs and CV axles. Some bolts that use an OE thread locker tape or thread locker under the flange like on some crank bolts use this x lb.ft + x degree also.
 
Originally Posted by kschachn
I think the only place I've seen an angle given without an initial torque is on spark plug boxes.
In that case, there's still an implied initial torque---the point at which torque to rotate the plug suddenly increases because the gasket has made contact. That point is distinct enough that it isn't necessary to list a specific torque value.
 
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So I'm left a bit confused here. What are the experienced mechanics here doing? Are you relying on your own sense of torque and not using a torque wrench, or simply following an angle approach given on the spark plug box? To me, this angle approach leaves a lot to be desired unless one is using a tool with a angle display. I took careful note of the torque wrench placement and sometimes it was a bit before 12;00 and other times a bit after 12:00 due to alignment between the spark plug socket and the spark plug. For the rear three it was even more challenging to comtemplate relying this approach as I had to reposition the torque wrench 3+ times. Therefore, judging where to exactly stop (say at 6:00 for NGK's 1/2 turn or 8:00 for NGK's 2/3 turn) is not easy due either to starting spot even when a full arc was possible, or adding up segments for multiple turns. I am an extremely careful person and wanted to do this right and hence deferred to my official Nissan factory service manual which says nothing about degrees to turn and only gives a spec range of 14-22 lb ft in the maintenance section. I'm pretty sure a Haynes manual would also strictly specify a torque value. It somewhat distresses me to think that despite all my careful planning and execution using the best tools and taking my time, something could have been damaged here on a car I have owned since new.

I was looking at my emails to NGK before I started this job and I even asked them if they themselves had compared their own torque angle values to supposed torque levels such rotations achieve, and the technician said he was not an engineer and had no idea how that was derived. In another email, the technician (think it was a different fellow that answered) said these compression washers are not an exact science and he simply torques to 20 lb ft personally leading me to conclude a quality torque wrench would be the safest way to do this job. A final inquiry to NGK about my experience resulted in a reply that as long as the torque wrench was calibrated, 18 lb ft is 18 lb ft regardless of where I ended up in terms of rotation.

In any case, if we assume 2/3 is the maximum amount the spark plug should have been turned, what is the forum's conclusion about turning it to approximately 7/8 turn max. From my calculations from thread pitch of the 14 mm plug of 1.25 mm/revolution, I calculate going from 2/3 turn to 7/8 turn would be an additional 0.26mm or 0.010". That doesn't seem like a lot to me personally - and if any damage were done, wouldn't that be just a bit of thread stretch at best?
 
NGK isn't concerned about torque. They are concerned about how much you crush the washer. They just want it to seal and not blow out. If you had chased the threads before installing the spark plugs, you probably could have screwed them just a little bit deeper and would have reached your torque with a little less angle.

It's not worth worrying about, you are within the acceptable range. You aren't going to damage the threads, just the degree of how much you chrush the washer. Notice that they gave a range of degrees and the manual gives a range of torque. If, instead of concentrating on a specific torque value, you used the recommended 1/2-2/3 turn. I believe you would find that it would fall within range of torque specified in the manual.
 
Originally Posted by user52165
Originally Posted by A_Harman
Originally Posted by tundraotto
Originally Posted by JOD
NissanMaxima said:
Hi all:
Keep in mind, torque values are just a proxy for bolt tension. What really matters is the bolt tension, and for that angle torque is almost always more precise.


THIS - SO MUCH THIS....


Yes, yes. Turn angle is much more consistent than torque.



But how specs will list and publish angle? Compared to torque specs?


Ex. 55NM + 90%
 
Originally Posted by NissanMaxima
....the "torque angle" method can be used. For the plug I used, they say 1/2 to 2/3 of a turn will produce their recommended torque of 18-21.6 lb ft of torque.

When do you 'start' the 1/2 to 2/3 of a turn ? That's the tricky part. When it's "snug" ? What does "snug" mean ? Three different people will have three different levels of snug, I'll bet.
 
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