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Torque Spec For Spark Plugs?

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#1 Airspeed-Alive



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Posted 18 April 2009 - 01:15 PM

Just wondering if anyone knows off hand how much I should torque the spark plugs in our 03 Silverado 5.3L.

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#2 bubba33



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Posted 18 April 2009 - 05:45 PM

I have no clue never used a torque wrench on plugs before. I have just used a 3/8 ratchet and snuged them up, maybe a 1/4 turn when it gets tight.

#3 mggray



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Posted 21 April 2009 - 06:40 AM

This is a guide I found on NGK's website:

1. Installing Spark Plugs

Torque is one of the most critical aspects of spark plug installation. Torque directly affects the spark plugs' ability to transfer heat out of the combustion chamber. A spark plug that is under-torqued will not be fully seated on the cylinder head, hence heat transfer will be slowed. This will tend to elevate combustion chamber temperatures to unsafe levels, and pre-ignition and detonation will usually follow. Serious engine damage is not far behind.

An over-torqued spark plug can suffer from severe stress to the Metal Shell which in turn can distort the spark plug's inner gas seals or even cause a hairline fracture to the spark plug's insulator...in either case, heat transfer can again be slowed and the above mentioned conditions can occur.

The spark plug holes must always be cleaned prior to installation, otherwise you may be torquing against dirt or debris and the spark plug may actually end up under-torqued, even though your torque wrench says otherwise. Of course, you should only install spark plugs in a cool engine, because metal expands when its hot and installation may prove difficult. Proper torque specs for both aluminum and cast iron cylinder heads are listed below.

Spark Plug Type
Thread Diameter Cast Iron Cylinder Head (lb-ft.) Aluminum Cylinder Head (lb-ft.)
Flat seat type (with gasket) 18 mm 25.3~32.5 25.3~32.5
" 14 mm 18.0~25.3 18.0~21.6
" 12 mm 10.8~18.0 10.8~14.5
" 10 mm 7.2~10.8 7.2~8.7
" 8 mm -- 5.8~7.2
Conical seat type (without gasket) 18 mm 14.5~21.6 14.5~21.6
Conical seat type (without gasket) 14 mm 10.8~18.0 7.2~14.5 <= Should be this plug.

Edited by mggray, 21 April 2009 - 06:55 AM.