Spark plug seal

[Tiger]

Hello Gents
Having difficulty getting a good seal on the plugs.
I have fitted Champion D16 which have a chamfered edge the head is flat at the plug recess.
Anyone else had the same issue.
I notice the original AGK plugs have a flat edge.
Comments please
Regards
               Tim

[John Cornforth]

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.

[Colin Wilks]

I fitted D21s to the 65 engine after its rebuild and they all leaked badly. This was the first time it had happened to me so I was surprised. I replaced them with a new set and made sure the sealing surfaces were absolutely clean and no problems since. I think today's plugs are just not made as well as they once were. I suspect my leaks were down to insufficient torque and less than perfectly clean sealing surfaces.
The Champion website recommends:
Torque - new plugs 35 ft/lbs
Reinstalled plugs - finger tight plus 90°

[gezparton]

I have used copper washers available from Green Spark Plug which give a good seal.