2001 ford F150 supercrew 5.4 engine 4x4 The truck now has 130000 miles on it and about 50000 miles ago it blew the plug out of the nr.4 cylinder. I got a tap to clean out the threads and re inserted the plug. About 5 days ago wlile driving home the plug blew out again still form the same cylinder. This time it took 75% of the threads from the head. Has this been a problem with this type of engine or am I just Snake bit?
Since the plug blew out 50k miles back running a tap back through the threads and reinserting the plug is not the answer. The threads are damaged goods at that point and it’s a miracle it stayed in as long as it did.
There’s been some problems with plugs blowing out of these engines but the main cause IMHO is overtightening of the plugs. The spec is around 15 ft. lbs. and that is too much for shallow threads on an aluminum head.
Other contributing causes could be the fact that a 1/2" drive torque wrench is not going to be that accurate at low settings; even if has been calibrated.
Another factor is that the majority of people do not use a torque wrench anyway and that includes most professional mechanics. In the latter’s case it can be said that many develop a “feel” for this stuff and can get it close without the use of a torque wrench due to repetition.
IMHO, 15 ft. lbs is too high anyway for a tapered seat plug on an aluminum head. Maybe more like 7-8. Snugged, basically.
There are several methods of repairing the plug hole with various inserts, etc. and this should have been done the first time it popped out.
Here’s one example.
http://www.timesert.com/html/sparkplug.html