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Doing some PM on new-to-me '89 760 TI. I removed the plugs to discover that #1 and #2 were not seated properly. At least that is what I think is going on.
The threads, base of the plugs, and even the insulator on #1 were stained with oily residue. The plugs in positions #3 and #4 did not have this condition, however #4 was tough coming out -- no sign of antisieze anywhere. It looks like since the plugs were not properly seated that Exhaust and combustion gasses have been 'blowing by' the threads. The electrodes looked fine so I cleaned the plug threads added antisieze and reinstalled the same plugs (Auto store only had 3 NGK BPR6EY, same as BPR6ES with "V" electrode. (Based on postings here, I electeded to exchange the BPR5EY that NGK recommends.)
The threads in the head are still "gummy" and it was hard to feel when the plugs were properly seated. They all torqued up and there is no indication that any of the threads in the head are stripped. I thought #1 was wasted for a couple of seconds, but it was just grabbing and letting loose as I tightened the last thread or so into the head. I think that since the plug wasn't seated fully before, the inner-most threads of the head were loaded with deposits.
Is there a good way to clean up the threaded holes so I can be sure I am getting the proper torque when I put in the new plugs. I was thinking of lacuer thinner on a brush but I am cocerned that the residue will tend to drip into the cylinder. I think chasing the threads is overkill and since the threads are not deformed, it could cause as much harm as good. Any other ideas?
Thanks for your help.
Dan
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