OVERKILL
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Originally Posted by Ws6
Originally Posted by HM12460
It's a GT, so it has the 4.6 2 valve s.o.h.c. engine factory rated at 260 horsepower. Ford fixed the intake manifold issue for the '02 model year, but I am wondering if the 2003-04 model year with this engine had the spark plug ejection/stripped threads issue? Please comment if you have any knowledge or first hand experience with this.
My Dad went through millions of miles on 2V 4.6L Ford mod motors. Never once did he have an issue with stripped plugs. Of course, millions of miles and a dozen cars is still a pretty small sample size, realistically. I wouldn't stress.
It seemed to affect the cars (and 4.6L engines) less for whatever reason, I assume due to lower cylinder pressure from the shorter stroke.
But this wasn't an issue that just cropped-up, it usually happened after the plugs were changed because of damage (marring) that happened to the threads during plug removal. Ford's official torque spec, it has been argued, was too low and many places have advocated essentially doubling it to prevent the issue.
In a nutshell: There are only three threads at the bottom of the plug tube where it goes into the cylinder. Most (all?) of the OEM plugs only featured threads at the bottom of the plug body to align with this setup. It was determined by whomever engineered the heads that three threads were sufficient for the application. This made assembly of the engines easier because the plugs would "self centre" in the holes when they were slid in from above, due to the unthreaded section, decreasing the time required to install them. This was beneficial because the plugs are down a pretty deep angled hole. These threads, being in aluminum, and right at the combustion chamber interface with a bit of the plug threads protruding into the chamber, could easily become damaged when the plugs were removed by deposits that had accumulated on the plug threads. This would lead the threads suddenly failing and the plug dramatically blowing out. On the other hand, the argument that if you increase the torque spec that this doesn't happen is an interesting twist. Mine were all torqued to the original Ford spec and #8 definitely backed out by itself (became loose) before ejecting. It sounded like an exhaust leak (which I also had, confounding things further) and was present for quite a period. Had I picked up on what I was hearing before the plug launched, re-torquing it might have prevented the ejection.
Ford later redesigned the heads to have a full 8 threads, and all plugs sold for these applications had a fully threaded body after a certain time period.
Originally Posted by HM12460
It's a GT, so it has the 4.6 2 valve s.o.h.c. engine factory rated at 260 horsepower. Ford fixed the intake manifold issue for the '02 model year, but I am wondering if the 2003-04 model year with this engine had the spark plug ejection/stripped threads issue? Please comment if you have any knowledge or first hand experience with this.
My Dad went through millions of miles on 2V 4.6L Ford mod motors. Never once did he have an issue with stripped plugs. Of course, millions of miles and a dozen cars is still a pretty small sample size, realistically. I wouldn't stress.
It seemed to affect the cars (and 4.6L engines) less for whatever reason, I assume due to lower cylinder pressure from the shorter stroke.
But this wasn't an issue that just cropped-up, it usually happened after the plugs were changed because of damage (marring) that happened to the threads during plug removal. Ford's official torque spec, it has been argued, was too low and many places have advocated essentially doubling it to prevent the issue.
In a nutshell: There are only three threads at the bottom of the plug tube where it goes into the cylinder. Most (all?) of the OEM plugs only featured threads at the bottom of the plug body to align with this setup. It was determined by whomever engineered the heads that three threads were sufficient for the application. This made assembly of the engines easier because the plugs would "self centre" in the holes when they were slid in from above, due to the unthreaded section, decreasing the time required to install them. This was beneficial because the plugs are down a pretty deep angled hole. These threads, being in aluminum, and right at the combustion chamber interface with a bit of the plug threads protruding into the chamber, could easily become damaged when the plugs were removed by deposits that had accumulated on the plug threads. This would lead the threads suddenly failing and the plug dramatically blowing out. On the other hand, the argument that if you increase the torque spec that this doesn't happen is an interesting twist. Mine were all torqued to the original Ford spec and #8 definitely backed out by itself (became loose) before ejecting. It sounded like an exhaust leak (which I also had, confounding things further) and was present for quite a period. Had I picked up on what I was hearing before the plug launched, re-torquing it might have prevented the ejection.
Ford later redesigned the heads to have a full 8 threads, and all plugs sold for these applications had a fully threaded body after a certain time period.
