Spark Plug Inspection

[John L.]

Hello all, I have a 66 big block in which I installed new spark plugs 15 years ago and have not removed them since. The car runs fine but I am curious to take them out and give them a look. There's about 5,000 miles on them. Now my question, is it generally recommended that that after some period of time, be it 5 yrs, 10yrs, etc, that plugs should be removed not only to examine them but also avoid seizing issues? Their Autolite plugs and don't believe I used anti-seize when they were installed. thanks

[Ken A.]

Re: Spark Plug Inspection

The rule is: If it will still pull 6500 in 2nd gear, then close your toolbox. They are AG32's, right.

[John L.]

Re: Spark Plug Inspection

No the plugs are 403's, just looking at the heat range index on the Autolite web site and these plugs are in the middle of the heat range, resistor plugs with 3/4 inch reach. Would someone know their equivalent heat range to an AC plug (44, 45?)

[Duke W.]

Re: Spark Plug Inspection

If you insist on Autolite plugs simply use their online cross reference for the AC 45XLS, or if Autolite doesn't offer a non-resistor plug, cross the R45XLS. The original AC plugs(43N I think) were heat range three, which is way too cold for normal road and highway driving. AC heat range "5" will stay cleaner/last longer in normal road use. Chevrolet was very conservative on heat range. I guess they thought everyone would be doing a couple of laps at Sebring on their way to work in the morning. For normal use AC heat range 5 or equivalent in another brand is best regardless of horsepower rating, but install heat range three if you plan to hot lap a race track or run the 92-mile Silver State Classic Challenge open road race at top speed.

Seizing can be an issue with time, particularly with Al. heads, but not so much with CI heads. Since these are gasket type plugs if you reinstall them you should use new gaskets although used gaskets will usually seal with proper torque. If you do use anti-seize compound, use it very sparingly. I've seen plugs with anti-seize that looked like it was globed on with a soup ladle.

Back in the sixties when I had to remove and clean the AC 44 plugs on my 340 HP SWC every couple of thousand miles due to high rev breakup I bought a box of 100 AC Spark Plug gaskets. That was before I figured out that the 44s were 1) too cold and 2) the breaker plate was wobbly, which caused a major loss of dwell angle at high revs that reduced spark energy below the minimum to light the fire. Live and learn!

I also recommend installing spark plugs with a torque wrench to the recommended torque value in the service manual. This should be easier to do on a BB than a SB.



Duke

[Frank D.]

Re: Spark Plug Inspection

I heard tales of poor fuel distribution and other such myths on my dual quad '61 and after 5,000 miles I pulled the plugs. As you can see -- very nice on modern fuel with ethanol.