Spark plug torques (Was Spark plug socket)

[jim-larsen@xxxxxxx]

In the Oilheads-Digest V2 #33 Kent stated that Bosch has essentially eliminated torque-wrench specs. That is not so! Bosch actually recommends that when installing spark plugs to use a torque wrench and gives the correct torque that should be used in ft.-lbs.

See: http://www.boschusa.com/AutoParts/FAQs/SparkPlugs/

It then goes on to state that if a torque wrench is "not" available, hand tighten the plug until it is seated in the cylinder head. Spark plugs with gaskets should be tightened an additional 900. Spark plugs with tapered seats should be tightened an additional 150.

As Gator in Dallas stated, you also can wind up stripping out the spark plugs threads of the cylinder head. Gator is very correct with his statement!

Marco replied to Gator in Dallas with: Hmmm, you might be surprised. There's a table on page 1404 of Machinery's Handbook 25 that notes the accuracy of bolt preload methods.

Marco, you cannot compare torqueing a bolt with torqueing a spark plug. A spark plug is an assembly of parts. If undertorqued you stand the possibility of the spark plug loosening. Worse yet, if a spark plug is overtorqued you stretch the spark plug components to where the threaded portion of the spark plug pulls the outer electrode/s away from the center electrode which is retained by the spark plug seat. This has been instructed to me in every automotive and aviation maintenance class/seminar Ive taken since the 1950's.

Discussing properly torqueing items such as spark plugs, drain plugs, bolts, etc is like discussing religion and politics. You always have dissenters and know-it-alls who dont really know-it-all! I've read for years how people state that they can torque items by feel. I've always offered for those people to demonstrate that talent in front of their peers in my hangar and get within the required tolerance . I have torque wrenches that measure from ounces of torque right up through torque wrenches that measure right past 500 foot pounds of torque. I also have torque wrench testers that go up to 1,000 foot pounds of torque.

If a person has not manufactured their own thin walled spark plug socket by welding, grinding, or turning existing sockets in a metal lathe there are many thin walled sockets available. The following tools are what I use: A 3/8" Drive Snap-On 6 Point 5/8" Thin Walled Deep Socket, # S9706KA, and a Craftsman 3/8" Drive Extension that locks on to the Socket, # 44357.

Just setting the record straight,
Jim Larsen

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