A few basics. Spark plugs do not 'wear out' with 'old age' i.e. 7 years.
It is 'use' that wears them out. The mileage done dictates how much has eroded from the points and with electronic ignition, even a significantly wider-than-standard gap will fire. So if the car won't start - it is highly unlikely that all 4 plugs have failed totally and at the same time.
Before potentially snapping a plug or stripping a thread, try
all other ways with the help of your ex-AA man - to get your engine problem sorted and started - because removing a 'tight' plug from an alloy cylinder head is best done with a
hot engine . The chances of damage are much higher with a cold engine.
If you do succeed in removing plugs without damage, the first thing to buy is a tube or tin of Copaslip. Apply it to the new plug threads and also get a small blob (the size of an emoticon [
] ) on the end of a small screwdriver and apply it to the threads in the head itself by rotating said screwdriver. Fit plugs and use a torque wrench rather than guesswork to tighten new plugs.
Anytime you remove plugs in the future, put another small smear on threads. The same goes for virtually all steel bolts into the alloy block - unless Porsche specify another product. I have been rebuilding all-alloy Rover V8's for about thirty years and Copaslip is a vital ingredient in stopping corrosion of steel threads tapped in alloy castings. With the 924S and 944 both tending to shear bolts on the water pump, if you are fitting a pump make sure threads are cleaned with a tap, copper grease thread
and the shank of the bolt so it will not seize in the plain section of the hole through the pump body.
Copaslip is also brilliant for putting on the locating register of Porsche alloy wheels.
I have just had to spend quite a time kicking alternate sides of a back wheel to break the 'bond' where a totally ungreased alloy wheel had corroded and locked solidly onto the ferrous hub. Previous owner or servicing garages were lacking in basic maintenance.
