Consequences of wrong spark plug gap?

Decolliber · 05-22-2004, 06:57 PM

Just got through replacing spark plugs for the first time since top end rebuilt two years ago. Noticed that the rebuilders (who had put in new plugs) left the WR7DC Bosch plugs with too wide a gap (.036", which is how they come out of the box) instead of regapping to the correct 0.028-0.032" gap. Does not seem to make any difference to the running of the engine.
What are the possible consequences of having a gap too big or too small?

CarreraS2 · 05-22-2004, 07:03 PM

As long as the engine was running fine, I don't think there is ANY consequence.

If a plug was gapped so wrong that it wasn't firing, you'd notice it. The engine would run really crappy on less than 6 cyls.

The difference you are talking about is a small one.

emcon5 · emcon5's Garage

Gap will grow over time as the center electrode erodes.

Don't sweat it.

Tom

johnsjmc · 05-22-2004, 07:40 PM

The gap will eventually grow from normal erosion of the electrodes.This used to be about .001 per 1000 miles with leaded gas. The gap growth is much less with unleaded The high output ignition systems will compensate for the wider gap by producing a higher voltage to continue to fire the plugs. If the gap gets too large the high voltage can leak out of the spark plug wires to ground especially in damp weather.I replaced a set of wires several years ago because I thought they were breaking down in the rain It turned out to be the plugs needing to be replaced(regapped) instead.

azasadny · azasadny's Garage

My plugs were gapped too wide and I had serious cold start problems that ended as soon as I regapped the plugs and installed new plug wires.

Sonic dB · Sonic dB's Garage

I gapped mine at the proper .27 or .28 (i forget) spec....and when I went to change them last week, the gap had grown to over .35 on most of them. its normal.

jluetjen · jluetjen's Garage

BTW - A wider gap can be good some times since it exposes more of the mixture to the spark which increases the likelyhood of combustion. On the other hand, I believe that if the gap gets to be too great that the increased resistance can burn out the ignition.

RoninLB · 05-23-2004, 05:38 AM

a dyno could show the proper gap. Slowly increase the gap and top hp will slowly increase. at some point hp will start to fall. then readjust to previous gap. I never did this. I only read about it. Naturally the wider the gap the more load on the ignition.

Reaction · 03-09-2012, 10:54 AM

The gap will for sure increase as you drive the vehicle and that's normal. Most of the time you won't have to gap your plugs if you purchase the correct plugs that are recommended by the manufacturer. All this info should be on the spec sticker when you pop your hood.

DRACO A5OG · DRACO A5OG's Garage

Oh good, I was concerned after 2 years I changed cap, rotors and plugs and found the gap wide on all pre-gapped plugs. I attributed it to heat cycles, glad to read this is normal.

I think I may service the plug gaps every 6 months just to be sure. great more labor of love, does this never end???

rnln · 03-09-2012, 12:04 PM

I usually double check my gap, .028, but once I read a thread in here, I tried .039 - .04. I can not notice any different at all. I has been in there at least 2 years. I drive the car couple times a year.

911pcars · 03-09-2012, 01:54 PM

Mechanically bent metal has memory. That is, when closing a gap to adjust, then heated, the side electrode will tend to revert to its previous position (wider), and vice versa.

Sherwood

ratpiper71T · 03-09-2012, 02:05 PM

Steve W. recommended a .040 gap with MSD. Just a guess, but I'm willing to bet some $ he has done just that.

Quote:

a dyno could show the proper gap. Slowly increase the gap and top hp will slowly increase. at some point hp will start to fall. then readjust to previous gap. I never did this. I only read about it. Naturally the wider the gap the more load on the ignition.

dshepp806 · dshepp806's Garage

Come to think of it, I've never measured the gap on "removed" plugs,..but have certainly found better performance when changing the plugs out more frequently....(as well as distributor and rotor button).

Always at .028,,,,....

Best!

Doyle

DRACO A5OG · DRACO A5OG's Garage

Hell, coppers are cheap enough, huh?

dshepp806 · dshepp806's Garage

Precisely, DRACO!!!!!!!!!!!!

Bob Kontak · Bob Kontak's Garage

Gaps set at above the 0.040" - like at 50-60 thousandths - will give the juice a good reason to find a better ground point. That means that if your wires are tired the large gap may cause arcing between wires or to a metal ground (e.g., air conditioning support bracket) or into your hand because it is easier for the voltage to land there rather than jumping the electrode gap.