• From: Minneapolis, Minnesota
  • Registered: 2005-10-15
  • Posts: 288

Re: Spark Plug Torque, Anti-Seize, Thread Chasing, Rolled Vs Cut Threads

Ryan,

If the surface of the Champion spark plugs threads were so rough as to cause significant wear, then there should be a predictable number of times that you could remove and replace a spark plug before significant thread damage occurs.  I've R&R'ed at least 50 spark plugs in one spark plug hole while indexing my spark plugs.  The hole seems just fine.  How many times does one realistically remove and replace spark plugs over the life on an engine.

You argued before that you need to heat cycle the engine for a valid test.  Heat cycling shouldn't make that much difference, unless you were overtorquing your spark plugs or having corrosion problems.  Anti-seize compound significantly reduces or eliminates the corrosion problem.  Using a torque wrench with the proper setting for the lubricity of the anti-seize compound used will greatly reduce the possibiity of distorting the spark plug hole threads.

Ryan wrote:  "More surface area = less pressure, and vice versa.  A course finish means higher point pressures, means increased wear, lubricant or not."

With 18 ft lbs of torque, the spark plug threads are very lightly loaded, which means not much pressure and not much wear, especially with a lubricant such as anti-sieze compound.

One manufacturer of threading equipment claimed that their rolled theads were twice as smooth as their cut threads.  For discussion, Let's assume this is also true for spark plugs.  If you can remove and replace a Champion spark plug 500 times before the spark plug holes threads were damaged by wear, and you could R&R an NGK spark plug 1,000 times before significant wear damaged occured, would it make any difference?  Some day when I'm really bored, maybe I'll do a test and find out.

If you don't think my findings are acceptable for a case study, let's see your data.  At least I've done some actual testing.  At this point you are assuming that NGK spark plugs have smoother threads than Champion.  That is certainly possible.  But until you have actually measured the thread finish of the two spark plugs, you're just guessing.

I also find it interesting that if cut spark plug threads were causing so much damage to aluminum cylinder heads, that the spark plug manufacturers with rolled threads wouldn't pick up on that and advertize that their plugs are so much superior.

The biggest reason that rolled threads are used for screws and bolts, is that it is cheaper to make bolts and screws that way.  Most applications are not so critical that it would make a difference.  If I'm going to get anal about threaded fasteners, I'll pay more attention to something critical like rod bolts.

As far as stress risers in the soft Aluminum threads, get real.  The cutting of the spark plug threads themselves would have caused stress risers many magnitudes of order greater than what the spark plugs could do the the threads.

If you really want to get anal, there are thread designs that are far less likely to cause stress fatique than the thread designs we use for cutting spark plug holes and making spark plug threads.  For that matter, the thread design used for most bolts, nuts and threaded holes is inferior to what they could be using, from a stress fatique standpoint.

You previously insinuated that I don't know how to index spark plugs.  I use a the same junk cylinder head and install the spark plugs with the anti-seize compound.  After the spark plug is torqued to 18 ft bs, I note the position of the spark plug electrode.  I can install any of my calibrated spark plugs in my engine, and if the spark plug is not in the correct postion I can determine how many degrees change is needed and select a calibrated plug that will install in the position I desire when torqued.  Once the spark plug holes in the cylinder head are also calibrated, I can pick the right calibrated spark plug every time.  Calibrating your spark plugs ahead of time is an efficient way to be able to index spark plugs.

Whether or not my spark plugs are indexed in the optimum position or not may be debateable.  However, they will all be in the same position.  I want as much uniformity as possible.

Scott Novak

32 Reply by rcb78

  • rcb78
  • Guest

Re: Spark Plug Torque, Anti-Seize, Thread Chasing, Rolled Vs Cut Threads

Hmm, didn't you say you were some sort of tech or something?  One would think you'd have a better grasp on what makes up a valid test.  What you have done is in no way scientific, period.
18 [ft*lbs] lightly loaded, who are you kidding?  For a 14x1.5 fastener (stock plug thread size), we'll assume SAE grade 5 since plugs don't need to be strong, you're looking at a yield strength of around 92,000 psi (SAE spec).  Torque spec is 75% of yield at around 90 [ft*lbs] for a zinc plated fastener, that's 69,000 psi.  Now translate to 18 [ft*lbs] and you get 13,800 psi in tension on that fastener.  Hmm, 13,800 psi, lightlly loaded, I don't see it.
Nice,, twice as smooth, twice the life.  Go back to school, it doesn't work that way.
I'm done.  You've proven you can't back up your claim.  You're the one trying to prove something here, no one else.  If you can't accept your wrong, then I can't help you.  --Ryan

  • From: Minneapolis, Minnesota
  • Registered: 2005-10-15
  • Posts: 288

Re: Spark Plug Torque, Anti-Seize, Thread Chasing, Rolled Vs Cut Threads

Ryan,

Depends on your definition of lightly loaded.

18 ft lbs is about 80% less torque than the 90 ft lbs you cited.

18 ft lbs is about 38% less than the Bentley manual's recommendation of 29 ft lbs torque for spark plugs. (Which I admit seems excessive.)

Scott Novak

  • From: Minneapolis, Minnesota
  • Registered: 2005-10-15
  • Posts: 288

Re: Spark Plug Torque, Anti-Seize, Thread Chasing, Rolled Vs Cut Threads

Ryan,

You haven't even claimed to have even seen a single case where cut threads damaged a spark plug hole.

You haven't given us measurements of the surface finish of a cut spark plug thread versus a rolled spark plug thread to prove than the rolled threads are actually smoother.

You haven't given us results of any testing that showed that rolled spark plug threads have lower friction that cut threads, while being torqued.

You haven't given any evidence to show that rolled spark plug threads cause less wear on spark plug hole threads, that have been lubricated with anti-seize, than cut threads.

You've given no evidence whatsoever to back up your claim that cut threads will cause significant damage to aluminum spark plug hole threads.  Only hearsay that cut spark plug threads are bad and should not be used.

Nobody else here has claimed to have seen a spark plug with cut threads damage aluminum holes threads.

On the other hand, in over 30 years of using Champion spark plug with cut threads, I have never seen any damage the the spark plug holes.  After removing and replacing over 50 Champion spark plugs in the same hole, in an worn out junk head, I haven't seen any damage.

If cut threads play any part at all in aluminum thread damage, it it probably very small in comparison to the damage caused by:
Over-torquing.
Failure to use anti-seize compound.
Cross-threading.
Failing to clean the spark plug threads with a chaser, and the resulting bad habit of wrenching spark plug into the holes, which increases the risk of cross-threading, instead of screwing them in by hand.

I have seen way too many cases of incorrect failure analysis.  I believe the idea that cut threads significantly damage spark plug holes is one of them.  Until I actually see some credible evidence, I'm calling it an Urban Myth.

Scott Novak

35 Reply by rcb78

  • rcb78
  • Guest

Re: Spark Plug Torque, Anti-Seize, Thread Chasing, Rolled Vs Cut Threads

Scott Novak wrote:

Ryan,

Depends on your definition of lightly loaded.

18 ft lbs is about 80% less torque than the 90 ft lbs you cited.

18 ft lbs is about 38% less than the Bentley manual's recommendation of 29 ft lbs torque for spark plugs. (Which I admit seems excessive.)

Scott Novak

Fine, you want one more go around, I'm game.  I did in fact cite 90 [ft*lbs] as a reference, but only to show you how I arrived at 13,800 psi achieved with ONLY 18 [ft*lbs].

I don't have to give evidence to back my claim unless you just don't have a clue, something I'm beginning to suspect.  YOU found a source agreeing with my claim that the surface finish is rougher by 100% no less.  That one little piece of information backs all my claims no matter how you try to twist things around to suit your pride.  Quit getting so pissed off everytime you're called on bad or incomplete information.  I'm not doing this just to push your buttons, I could care less about you and all your misconceptions.  I do however have a problem with anyone who gives erronious or incomplete advice.  This hobby is already dying, no need to help it along.  --Ryan

  • From: Minneapolis, Minnesota
  • Registered: 2005-10-15
  • Posts: 288

Re: Spark Plug Torque, Anti-Seize, Thread Chasing, Rolled Vs Cut Threads

Ryan,

Are you not reading carefully or deliberately trying to distort what I said?

I said that a manufacturer of thread cutting equipment claimed that their cut threads were twice as rough as their rolled threads.  That does not mean that Champion's threads will be rougher than NGKs threads.  For all you know Champion could have smoother threads than NGK.  Or Champion could have threads 10 times rougher than NGK.  YOU DON'T KNOW!

If you are going to claim that NGK has smoother threads than Champion, PROVE it with some measurements, or at least with advertised specifications from NGK and Champion.

Secondly, even if NGK has smoother threads than Champion, you still haven't given any evidence to show that Champion's cut spark plug thread will cause any significant damage to aluminum spark plug hole threads within the expected life of the cylinder head.

You have made claims without any evidence, or even bad personal experience with Champion spark plugs, to back it up.

All you have given us is your personal OPINIONS which you have tried to pass off as fact.

If you have some credible evidence, let's see it.  Put up or shut up.

Scott Novak

37 Reply by gest

  • gest
  • Guest

Re: Spark Plug Torque, Anti-Seize, Thread Chasing, Rolled Vs Cut Threads

Can the two of you please go to a neutral corner and take a time out?

You've each said all you have to say and further repetition is becoming tiresome.

Neither of you has to have the last word.  We heard that about five posts back.

Give it a rest.