08-11-2022, 07:14 PM
Hi Tim
I am only aware of two types of plug seat, traditional ones with a flat part and a crushable washer (usually captive), and the less common "taper seat" ones without a washer (Ford once used to favour these, in 18 mm size).
At the transition between the thread and the flat part there may be a small chamfered area which might vary between manufacturers, but I presume this is accommodated within the crushed thickness of the washer. If it didn't, you would have to relieve the very top of the threaded hole in the head, but I have never found this necessary.
If you have used the correct torque and are still having sealing problems with the conventional washer type plugs, it may be that there is some roughness to the flat seating area on the head. It may be possible to reduce this by suitable machining/grinding/scraping.
I am only aware of two types of plug seat, traditional ones with a flat part and a crushable washer (usually captive), and the less common "taper seat" ones without a washer (Ford once used to favour these, in 18 mm size).
At the transition between the thread and the flat part there may be a small chamfered area which might vary between manufacturers, but I presume this is accommodated within the crushed thickness of the washer. If it didn't, you would have to relieve the very top of the threaded hole in the head, but I have never found this necessary.
If you have used the correct torque and are still having sealing problems with the conventional washer type plugs, it may be that there is some roughness to the flat seating area on the head. It may be possible to reduce this by suitable machining/grinding/scraping.