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. Proper torque specs for both aluminum and cast iron cylinder heads are listed below.""" Of course, you should only install spark plugs in a cool engine, because metal expands when its hot and installation may prove difficult. Serious engine damage is not far behind.Īn 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. This will tend to elevate combustion chamber temperatures to unsafe levels, and pre-ignition and detonation will usually follow. A spark plug that is under-torqued will not be fully seated on the cylinder head, hence heat transfer will be slowed. Torque directly affects the spark plugs' ability to transfer heat out of the combustion chamber. Torque is one of the most critical aspects of spark plug installation. Here is some good info from NGK on why torquing them is important. Wait, I take that back, once I overtightened one plug, and it had a hairline fracture to the insulator part like mentioned in the article, and I had a constant misfire till I replaced that plug. Why are they listed so high here, but my manual says 11 ft lb's?Īlso, I am not sure what the manual is talking about, I have no aluminum shields on my wires near the exhaust manifold on the front, there were never any there when I got the car at 27kĮDIT: Never mind, I remember asking this same thing a while back, I remember that the techs just had it wrong in that part of the manual, 20 ft lb's is right.Ĭlick to expand.I had never torqued mine either, but I'm sure I always got them close to being just right, as I've only ever broken a bolt when using a torque wrench, not the other way around, lol Now I am a bit worried because I looked at the torque specs listed here, and they say 20 ft lb's, so effectively I torqued mine almost 2x spec recommendations, I thought it felt way too tight when I was tightening them. Care should he taken to ensure these heat shields are fully seated. NOTE : On the 3800 engine, aluminum heat shields are used over the spark plug boots on cylinders which are close to exhaust tubing. I was looking over my maintenance manual making sure I had replacement intervals right with this Car Minder Plus app I am using, and I noticed something that has me a little concerned, my AllData manual says this.
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