![]() Either way, he got my brother’s car running again, but gave him the condition that he never try to change spark plugs again, or at least to never remove the one he installed. For some reason, a Heli-Coil wouldn’t work, he said. After my dad tore the threads out of the first spark plug hole, my brother chased him away from the project and drove the car on three cylinders to a friend of mine’s house, where my friend cut new threads and installed a different spark plug he had laying around with Loctite. My father likes to use a torque wrench on everything, and he ruined my younger brother’s opinion on them by insisting, against my brother’s will, upon installing spark plugs in his first car using a 1/2" drive torque wrench. The given spec will be at the bottom of the torque wrench’s range, which is typically less accurate than the middle of their range. If you do use a torque wrench, use a 3/8" or 1/4" drive tool, NOT a 1/2" drive torque wrench. Snug with a short 3/8" drive ratchet is good for spark plugs. As long as it holds compression, and doesn’t work its way loose with time, it’s tight enough. If you hear a compression leak, or feel it when you hold on the plug wire boot, the plug needs to be tighter. If the car has exposed plug wires, you can tighten the plugs and run the engine. Pretty soon you just learn how it feels when it’s ready. I’d advise learning with a torque wrench, and start on the low end of the torque. He said to tighten it snug, and turn on the water and see if it leaked. He told me I didn’t have to knock it out of the park when tightening a threaded connector. When I had a plumbing project, a plumber gave me some good advice. Just turn it for as long as it turns easily, then turn it a little more. It’s a lot harder to overtighten the plugs with that tool. That won’t always break the old one loose, though, so a socket and ratchet may be needed for that. I use one of these to tighten, when it’ll fit. This also falls into the grenade category.) (Not spark plug related but consider the rocker arm sideplay spec on a Harley Davidson Shovelhead engine. If a torque wrench is used it should be an accurate 3/8 or 1/4 drive tool and one should adhere to the low side of the tolerance range. On one application an 8 pound reading was given and another manual stated 17 Ft. so it’s a grab bag anyway of what is allegedly correct anyway. I’ve seen specs for a certain application given as a certain amount in one book, something different in another, still something different on an internet site, etc. It’s quite possible to pull the threads with either specification, especially on a short reach or shallow thread depth spark plug. One book of mine gives the torque on an aluminum head Ford 4.6 at 7 to 14 Ft. Feel is far more trustworthy than an iffy torque wrench (especially if it’s a 1/2" drive at low settings) or a given spec which will vary depending on the source. Speaking for myself and other mechanics I know, none of us use a torque wrench. ![]()
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