I ran a JP 2 for years and it had the convex face. When screwed in it would seal against a face and when screwed out the back side would seal against another face to stop exhaust fumes leaking up the threaded shaft. It was a hand start unit. Worked well.
Blue
Thanks for that, Blue. So it was a real Lister part, just one we are mostly not familiar with. I may have to just try that rather than use a standard COV.
Because:
I have tried to remove the "main plug".......the concave part that fits into head.......no joy. Used the wooden plug method, but it would not come free. Even though a bit of oil squirted caused the engine to fire. Repeated this a few times, but the plug would not free up.
I put a bit of clay into the Main plug stuck in the head and also into a normal main plug that came with a new COV. Molded to shape, the dimensions are easily seen to be different. The new, normal main plug is about 1/4" shallower than the unusual one in the original photos. Looks as if the main plug part is specific to the type of COV.
Any one have some alternative ideas for removing a reluctant main plug?
All suggestions welcome!
Cheers,
Hugh