I changed the spark plugs in a Mazda3 this weekend -- the Mazda MZR engine which is essentially the same engine as the Duratec 23/20 used in the Ford Focus. These are taper seat plugs, and I think every other vehicle with aluminum heads I've changed plugs on uses gasket seat. The gasket seat plugs I've done call for somewhere around 20-25 ft*lbs of torque on installation, while the Mazda's service manual called for 8-10 ft*lbs.
I was surprised and had to double check when I read that spec. 10 ft*lbs is nearly "finger tight with a quarter inch drive ratchet"! Hard to believe the plugs will actually stay in, but then they seem to have plenty of threads.
Am I right in concluding that ~10 vs ~20 ft*lbs is a difference governed by the presence or absence of a crush washer to seal against the head? Is this because the taper seat offers a better seal and so less torque is necessary, or is it because the gasket simply allows more torque to be applied safely?
I was surprised and had to double check when I read that spec. 10 ft*lbs is nearly "finger tight with a quarter inch drive ratchet"! Hard to believe the plugs will actually stay in, but then they seem to have plenty of threads.
Am I right in concluding that ~10 vs ~20 ft*lbs is a difference governed by the presence or absence of a crush washer to seal against the head? Is this because the taper seat offers a better seal and so less torque is necessary, or is it because the gasket simply allows more torque to be applied safely?
