The Stovebolt Site Forums The Shop Area Engine Shop Spark plug gap

I was reading the thread about the HEI ignition and the recommended gaps were anywhere from .045 to .060. Is there a point on a gas engine that is too much? The reason I wonder is, that on a propane engine you should run around .025. I had a 318 Chrysler with electronic ignition on an irrigation pump that I fought for years trying to get it to start and run right. It always started hard and always seemed to have a half ways miss in it. I can't tell you how many ignition components I changed trying to get it get it to run right. I was running about .045 on the plugs. I thought the wider the gap, the better. One day, out of frustration I called probably the second best mechanic in the county and he asked what the plug gap was. I told him, and he said it was far too wide for propane. He recommended .025. It made a whole different engine out of it. It started instantly, sounded perfect at all rpms and loads and took less fuel. He was truly an excellent mechanic. He could tell by looking at the plugs almost anything that was wrong with the engine.

He died 2 years ago coming up in June. I sure miss that guy. As good as he was as a mechanic, he was even better as a person.

Im using the pertronix set up on my 1950. 235 12v, They recommend .005 over factory.

As did other members on this forum when I posted a similar question.

I have them set at .040 now.

Good Luck

Chev. specified .045 with their HEI ign. The Petronics uses stock or near stock coil & the plus.005 sounds right. If you get too much gap it is easy for the spark to leak out before it gets to the electrods. Some GM cars used .060 & .080 gaps & had starting problems in cold & damp weather.

we are running a Langdon HEI unit in a 1957-235. We followed Toms advice as to the gap and type of plug. What we don't know (never having an HEI unit) how many miles before we need new plugs? The plus in my wife's car will go 100K before changing!!

Thanks for the advice and Happy New year to all!

Steve

Spark plugs last a lot longer then they used to because the no lead gas does not have the erosion effect the lead had. We used to replace plugs on these old trucks about every 10,000 miles. You can't run them 100,000 like the modern car's though. About 25,000 would be about right. You can inspect 1 or2 at random occasonally & check for foriegn deposit buildup & erosion. If they are OK keep going.