The Stovebolt Site Forums The Shop Area Engine Shop correct spark plug, and an answer about that little gasket

Happy Friday. Should be a good weekend to work on our old trucks, though still a little warm.

Regarding my '51 1/2-ton 216 straight-6, below I have links to web pages that show 3 spark plugs, with specs, from Autolite, and I ask which you believe is most appropriate.

This is Autolite model 86 (scroll up after landing on the web page), the plug I've been using the last few years (about 4 miles on 'em, but a whole lotta fouling), from NAPA.
This is Autolite model 85, the plug NAPA sold me yesterday (I'm changing out my plugs).
These two are very similar and I don't think I care about the difference between the two.

This is Autolite model 303, which is what I find when I use Autolite's product finder for my make, model, and year.

The differences are that 85/86 have a "tip configuration" of "Mid Projection", whereas 303 has a "Short Projection", and 85/86 have a "terminal type" of "Solid", whereas 303 is "Removable". Also, 303 is what the website recommends for my truck. 85/86 are recommended for V8s from 1955-57.

Any thoughts on whether it really matters?

Finally, regarding the mystery (for many of us), of which way the plug gasket should be oriented, check out this web page. Many of you will be surprised, as I was.

Looks like I've been doing the plug gasket wrong my entire life.

So is partial turn past finger tight equal to quantitative torque settings? Are those substitutes for folks that don't have a torque wrench? Must also admit I never have used a torque wrench or followed partial turn guidance. Sure would be a little nervous about finger tight + 1/16 on my weedeater, much less SBC.

Why are you using Autolite plugs in a GM vehicle? I have always used what the manufacturer called for due to variations in heat range across the brands. If I am not mistaken I believe Chevrolet engineers called for AC plugs.

Interesting info. Personally I have never torqued a plug or paid attention to how far it turned after "hand tight". I just tighten them kind of tight but not too tight. The idea of hand tight, then turn a specified amount is a real bogus idea. A plug could stop anywhere due to strength of hand, due to hanging up on threads, due to dirt/grease in hole, due to hot motor, due to anything......and not be at a point called "hand tight". With gasket seal plugs, many companies say hand tighten until gasket touches the head, then 1/2 turn. Good luck with that. I say: Use a socket wrench with one hand only on the head of the wrench until plug is tight. Snug is a good word with gasket seal plugs. Don't have your hand on the handle of the wrench. It is nothing like tightening a bolt. NOT the same.

Any plug will provide a spark if the computer says it fits your application. Does not make any difference what brand. All the brands have various designs and materials. Various "models" of plugs. This "Hot" and "Cold" B.S. has nothing to do with the spark. A spark is a spark. A 216 is not in the world of precision performance plugs. As D.G. Denny says, it's closer to a lawn mower engine.

I always compare the old to the new regarding length of threads and overall stickout in case the counter guy made a mistake. I always do my own searching on all parts. I never accept a part that has been opened, dirty box or repackaged.
If the proper plug is fouling, I would blame the motor.

AC Delco is a R45(s)

Hey there, Fixit58. I went into NAPA asking for the AC 44-5 (per spec), and the parts guy, who is a second-generation store owner, said he couldn't get those but he could get the Autolites, and "there's not much difference because they're all made by NGK these days". (I'm guessing the 'N' is for Nippon, i.e., Japan). So I said "ok". But I do think I'll return them (never installed and in clean boxes), and look for the exact recommended plug. But I wouldn't think it matters a great deal. ???

Stock plugs used in the early days were AC-44 with .035 gap The AC44 has been discontinued but occasionally shows up on eBay.
Delco plug numbers de-code as follows: R=resistor type, 4=14 mm thread, next digit (4 or 5)=heat range (higher number is a hotter plug), S=extended tip. The R45S plugs are middle of the road heat range & should work fine if your engine is in good condition. Heat range is simply how fast heat is carried away from the plug. I believe the AC R45S is the correct modern plug for our “unmodified” 216 motors.
Harold

I've always run AC Delco R45's and have found them very easy to buy at most any FLAPS. Never knew to ask for the "S" version.

I've been told that by using the "S" version you get a cleaner burn and less fouling because the tip is a little deeper in the combustion chamber.
Harold

Try E3 plugs available online or at FLAPS. I use them on my 54-235.

The S type plugs are a modern replacement in o-head valve engines but should not or cannot be used in flathead engines.