51 8N side. Been about 3yrs/100 hours since I pulled plugs and checked the insulator color etc.. 1,2 3 came out easy as expected - but 4 wouldn't move. Careful application of pressure and some liquid wrench oil and it slowly started . . . but needed the wrench all the way till it came out. See pictures for thread damage. Autolite 437s.
I've been pulling/inserting plugs for 60 years so I'm 99.99% sure I didn't insert it cross threaded - I know that they go in by hand and then just tighten up the last half turn.
So - is this just a rust issue ? or what ? How do I clean the head threads - don't want to strong arm the new plug in. A YT search tells me I should be looking for a 14mm x 1.25mm plug tap but I've no experience in this area - what sort of problems am I going to fall into if I don't seek/follow forum advice/help ?
BTW - all 4 showed that combustion was healthy - almost makes me wish I'd left well enough alone - but NGK 3112 are waiting to go in .
I've been pulling/inserting plugs for 60 years so I'm 99.99% sure I didn't insert it cross threaded - I know that they go in by hand and then just tighten up the last half turn.
So - is this just a rust issue ? or what ? How do I clean the head threads - don't want to strong arm the new plug in. A YT search tells me I should be looking for a 14mm x 1.25mm plug tap but I've no experience in this area - what sort of problems am I going to fall into if I don't seek/follow forum advice/help ?
BTW - all 4 showed that combustion was healthy - almost makes me wish I'd left well enough alone - but NGK 3112 are waiting to go in .