spark plugs torque - Mercedes-Benz Forum
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#1 (permalink) Old 05-15-2008, 07:56 PM
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spark plugs torque

98 230, will be changing plugs this weekend. Do I really need to torque the plugs? If so.....at what torque.
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#2 (permalink) Old 05-15-2008, 09:01 PM
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Originally Posted by mista View Post
98 230, will be changing plugs this weekend. Do I really need to torque the plugs? If so.....at what torque.
It is always a good idea to use a torque wrench. For many things.

The torque spec should be on the package or even the plug. I think 18 ft-lb should be good.
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#3 (permalink) Old 05-15-2008, 10:03 PM
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Originally Posted by rpiotro View Post
It is always a good idea to use a torque wrench. For many things.

The torque spec should be on the package or even the plug. I think 18 ft-lb should be good.
+1 on 18 FT-LBS.

Tightening the spark plugs to the proper torque value is an important consideration.

Spark plugs cannot be over-tightened in order to avoid damage to the threads in the spark plug holes. Conversely, they cannot be loosely tightened since otherwise the combustion chamber would not be properly sealed, and to allow proper electrical and heat conduction to the cylinder head.

NGK recommends a torque range of 18 ft-lbs to 21.6 ft-lbs for their plugs (14mm, aluminum alloy head).
You can go to their web-site for more info:
NGK Spark Plugs USA


Bosch recommends a torque range of 19 - 22 ft-lbs. for their plugs (14mm).
Go to their website for more info:
http://www.boschautoparts.com/Resour...SparkPlugs.htm

I prefer to use the lowest value of the torque range to facilitate loosening and to prolong thread life.

Anti-seizing compound is not recommended since it can adversely affect proper torque reading, and electrical conduction. Anti-seizing compound is not required to facilitate the loosening of spark plugs since the spark plug manufacturers have already taken the required steps in the design of the spark plug to make anti-seizing compound unnecessary.

Last edited by techyiam; 05-15-2008 at 10:09 PM.
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#4 (permalink) Old 05-16-2008, 01:52 AM
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#5 (permalink) Old 05-16-2008, 03:06 AM
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Originally Posted by Bazzle View Post
I personally always smear a very thin layer of moly (black) grease on the threads.

Bazzle
Here is one opposing view:

NGK Plug Pro

I go further than that. I don't use anti-seizing compound even on re-installation. But experience goes a long way when torquing a spark plug on re-installation.

Last edited by techyiam; 05-16-2008 at 03:09 AM.
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#6 (permalink) Old 05-16-2008, 05:20 AM
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I have to agree with Bazzle on this one.
The problem with the NGK statement is that most people haven't a clue as to what the plating on the spark plugs might be, and that's where the rub lies. Just because a plug has a bright coating doesn't mean that it's the trivalent coating that is applied to the NGK or other plug that you might be installing.

Installing your plugs with a torque wrench is a great idea, but torquing to the lowest numbers isn't always the best idea. You don't always know what you getting when you tighten the item.
The problem with torque wrenches is that many (talking mostly click stop style here) will go off of calibration if mishandled or dropped. They need to be recalibrated on a periodic basis in order to insure that they are giving you what you ask for. How many people do you know that have EVER had their torque wrench calibrated? (No smart ass remarks here thank you.)

Adding a very small amount of anti seize to the threads or even grease does some things as you install spark plugs.

1- Give you a standard for torque, because there will always be some oil, grease, or something on the head threads that will give you an erratic torque or tightness, even though the applied torque might be exactly the same on all plugs.
2- The bond between aluminum and steel can destroy plug hole threads which will require fairly expensive repairs to be made. In many cases the plug threads have already been upgraded with other than just threaded aluminum.
3- Be very sparing with anti-seize, and ONLY on the threads, it’s a conductor of electricity, and will foul a plug in a heartbeat….

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#7 (permalink) Old 05-16-2008, 06:19 AM
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Personally I use a little bacon grease on my plugs - they torque down nicely and you have the wonderful smell of cooking bacon when you drive the car

Bruce is 100% correct about the calibration on the torque wrench. If you purchase one from Griots garage it includes life time calibrations.
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#8 (permalink) Old 05-16-2008, 10:41 AM
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Originally Posted by Bruce R. View Post
The problem with the NGK statement is that most people haven't a clue as to what the plating on the spark plugs might be, and that's where the rub lies. Just because a plug has a bright coating doesn't mean that it's the trivalent coating that is applied to the NGK or other plug that you might be installing.
Is anybody still seeing seizing problems (what brand and part number)?

My experience has consistently shown that engine performance and fuel economy can be gain if the threads are thoroughly cleaned, properly torque, and no anti-seizing compound etc are used.

Last edited by techyiam; 05-16-2008 at 10:48 AM.
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#9 (permalink) Old 05-16-2008, 01:11 PM
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#10 (permalink) Old 05-16-2008, 02:02 PM
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OP has a 98 C230, and my guess is that most likely he will be installing plugs from either Bosch, NGK, or Denso. These plugs have the protective plating. I see over-torquing as the one of the main causes for thread damage in alloy threaded holes in general. An accurate torque wrench is really necessary. The torque range specified for the NGK's is between 18-21.6 ft-lbs. That is not that wide a range. One can under- or over-shoot without an accurate torque wrench. What I have found to give the longest thread life is to have the threads thoroughly cleaned, accurately torqued, and use no friction modifier. This is especially true when torqued to the lower values of the range. This applies not only to spark plugs but bolts in general in alloy components.

But of course if the mechanic is not going to clean the threads, then if there is stiction, it is better to have some friction modifier applied than for the mechanic to use brute force to "push" it through. For myself, I clean the threads until I can screw in the plugs all way in with a light consistent finger pressure. Yup, it is a lot of work. But it is better than repairing damage threads.

Last edited by techyiam; 05-16-2008 at 02:07 PM.
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