[Tigers] Anti-Seize on Spark Plugs

[genepadgett at comcast.net]

Curt, my gin and tonic is encouraging me to reply :>) 

I intended my post to focus on the real objective of determining "how tight" the plug should be. Torque is a proxy for that clamping force and for a given clamping force objective is a variable depending on the lubrication or not on the threads. As you seem to agree, lubricated threads, having lower friction between them, will turn further before stopping at a specific torque. However, the lubricated installation will have a greater tension in the plug body, being stretched more. Or so I submit. 

Perhaps you can rationalize your view with ARP specifying lower installation torque for their head bolts depending on whether the threads are lubricated or not and what is the lubricant.. 

As for Harley specifying anti-sieze, I submit that they, like ARP, have determined what is the desired clamping force (i.e., stress within the plug and sealing objective) given the effect of the specified lubricant and written their spec accordingly. Not unlike ARP and their head bolts. 

To the extent that anti-sieze is in any way a lubricant is a separate question, but I subjectively submit it has some lubricating properties above zero. Whether it is materially different than dry is a totally different question. 

Cheers (!) 

Gene 



----- Original Message -----
From: "Curt Hoffman" <choffman9 at cinci.rr.com> 
To: tigers at autox.team.net 
Sent: Wednesday, April 18, 2012 11:27:13 PM 
Subject: Re: [Tigers] Anti-Seize on Spark Plugs 

Very common automotive blog material as to whether torque is affected by 
anti-sieze. Shows up on every car list I am on. I have seen engineering 
papers written on it. I personally, also being an engineer, subscribe to the 
side that torque is a static measure while the lubricants tend to more 
affect friction in movement. There is very little movement at the end of the 
torqueing of a bolt and I find it hard to believe the antisieze would affect 
the value to any great degree. Since my Harley recommends antisieze on the 
plugs, and are very careful about torques for everything on the engine, I 
stick with the "no real affect on torque value" position. 

Curt 

-----Original Message----- 
From: tigers-bounces at autox.team.net [mailto:tigers-bounces at autox.team.net] 
On Behalf Of genepadgett at comcast.net 
Sent: Wednesday, April 18, 2012 6:14 PM 
To: rfraser at bluefrog.com 
Cc: Tiger's Den 
Subject: Re: [Tigers] Anti-Seize on Spark Plugs 

Just a caution to all about specific torque figures. The 15 - 20 ft- lb 
figure in the shop manual is probably a dry torque figure. Anti-sieze on the 
threads acts as a lubricant. It will result in a considerably tighter actual 
clamping force (and stress on the plug threads) at a 15-20 ft-lb torque 
reading than you would have at the same torque and no anti-sieze . 

Gene 
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