After experiencing stripped threads on my old 88 iS 10+ years ago, I began hand tightening all my spark plugs and giving it an extra tug to be sure not to overtighten the spark plugs on all my cars. I have even seen this method suggested by manufacturers like Denso. Sounds like a safe practice right? ...wrong. I learned the hard way that loose plugs are just as bad as plugs put in too tight. There's a spark plug torque spec for a reason. .If you torque them too loose, they will back out and cause pre ignition which can also damage plugs and aluminum threads in addition to leaking cylinder pressure.
Had the plugs in my M52 back out, producing an audible knocking noise. I feared the worst but when I pulled the plugs, most of them were barely hand tight. The cylinder pressure was pounding them out. Luckily, I was able to torque them down without any issues and the noise is gone. My turbo m20 would experience misfires but I attributed that to spark plug temp ranges, gaps, old ignition so I changed all of that and guess what...it still misfires so I started looking at torque specs. Recommended torque spec for M20 is 17-23 ft lbs and my plugs were way less than that. I had hand tightened them before but now they were way less than that. Surely they backed out since I installed them but plugs shouldn't back out to begin with. Using a torque wrench on spark plugs seems kind of silly but it actually makes a lot of sense. Too tight and you risk stripping the threads, too loose and they will back out, cause pre ignition/misfires and potentially damage the threads, etc.
Obviously some things are more critical than others but torque wrenches should be used where ever possible IMO. Broken bolts/stripped threads could all easily be avoided with this good practice.
Had the plugs in my M52 back out, producing an audible knocking noise. I feared the worst but when I pulled the plugs, most of them were barely hand tight. The cylinder pressure was pounding them out. Luckily, I was able to torque them down without any issues and the noise is gone. My turbo m20 would experience misfires but I attributed that to spark plug temp ranges, gaps, old ignition so I changed all of that and guess what...it still misfires so I started looking at torque specs. Recommended torque spec for M20 is 17-23 ft lbs and my plugs were way less than that. I had hand tightened them before but now they were way less than that. Surely they backed out since I installed them but plugs shouldn't back out to begin with. Using a torque wrench on spark plugs seems kind of silly but it actually makes a lot of sense. Too tight and you risk stripping the threads, too loose and they will back out, cause pre ignition/misfires and potentially damage the threads, etc.
Obviously some things are more critical than others but torque wrenches should be used where ever possible IMO. Broken bolts/stripped threads could all easily be avoided with this good practice.
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