Re: '41 120 Sparkplug gap question

Posted by Ozstatman On 2017/5/6 19:37:02
Mea Culpa, just as Fred said: "The answer is that you gapped them incorrectly."

I sure did! But Your Honour, I'm pleading guilty with an explanation, here goes.

Over the years I've collected plenty of automotive stuff including 2 sets of feeler gauges. I'd actually never used one of the sets until I gapped the new plugs about a month a go. Set them to .030" or so I thought. Looking at that set of feeler gauges this morning found they are in mm sizes, so .30mm = .012"approx! When I regapped the plugs yesterday used my old set with .012"+.015" blades for a total of .027".

To answer your questions.

O_D, Any changes to the cylinder head since just before you've noticed this? - Head was surfaced 7 years ago when the engine was rebuilt and hasn't been off since then.

HH, I'd also be curious if the new plugs were the same as the old ones as far as reach and did the old use a gasket while the new did not? - New plugs are the same as old ones, UY6's, with one gasket on each.

Wes, Do you still have the previous plugs? If you do check the gap on them and I would look at them and see if you can see any difference between the new and old plugs. Plug gaps normally increase not decrease. - Old plugs seem to have opened up a bit.

Ernie, I would suggest pulling a couple of plugs and checking the gap. - Pulled 2 of the plugs this morning and they're still at .027". looking good!

Not an answer to a question, just something I want to say regarding my comment of, "On many previous occasions, for a range of 110's and 120's I've been associated with, have usually used .028" and this has seemed to work well." - The gauge I used when gapping those plugs was one of Wade's as all of that was done at the Workshop. The gauge was a wire gauge, being a ring with loops of wire around the circumference, one of which was .028", loved it. Didn't have to fiddle with blades to make up a thickness, very easy to use. If I ever see one at a swap meet I'll grab one for myself.

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