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Below is a collection of Jim Grant's Tech Tips sorted by Vehicle Make. These Tech Tips were answers to questions submitted to Jim by users over the course of many years.
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  Jim Grant's Tech Tips

91 Nissan SE-V6 Pickup Truck, Non-Removable Spark Plugs
Q: I have a '91 Nissan SE-V6 pickup truck. I had the 120,000 mile inspection/service performed. The schedule calls for spark plug replacement. When I went into pick up the truck they told me: "We could not remove the rear spark plug without use of excessive force and risk breaking the plug as that would cause an expensive head removal to remove and replace the plug. The plug was firing all right so we left it in and you can decide what to do later. However we are sure the plug is not cross threaded." The same service department had installed those spark plugs during the 72,316 mile service. Which brings these questions; 1. Since a spark plug is continuous metal, how could it break, leaving part of it in the cylinder head? 2. Can they, in fact, determine that it was not cross threaded? 3. Since they installed the plug would they not be liable for any damage or repair necessary to remove and replace the plug? 4. What course of action do you suggest?

A: A spark plug does have a continuous metal housing but, it becomes very thin at certain points. Forcing a frozen spark plug is almost a guarantee of snapping it off in the cylinder head. The length of the threads on the spark plugs for your vehicle is nearly 3/4 of an inch long. If the spark plug was cross threaded during installation it "never" could be fully installed. This condition would be visible at the spark plug and, once removed, there would be indications as well. The problem you are experiencing is not uncommon to engines with aluminum heads, it happens. All it takes is a small burr or piece of the aluminum threads to break, causing the spark plug to bind as it's being removed (which is not the fault of the installer). Sooner or later you'll have to find out what happened, the spark plug will have to be removed. With some luck and an experienced technician the spark plug can be removed without causing costly damage or the need to remove a cylinder head.

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