Setting the gap on spark plugs was one of the first things my father taught me to do when working on cars. This process was so simple. I was only 8 or 10 years old at the most and I learned to do it in about 5 minutes.
You might think that gapping spark plugs are a thing of the past. When your car, SUV, or truck needs new spark plugs you buy new ones and install them, right? Unlike spark plugs and points in engines of the past, you don’t need to gap spark plugs regularly.
That’s a nice thought, but it isn’t true.
OK, well ignition points are no longer necessary unless you own a classic car, but you will still need to gap those spark plugs, new or not.
Why? Think about it. The truth is that spark plugs are manufactured to fit a wide variety of engines. Not all these engines, by the way, use the same spark plug gap. The manufacturer will most likely gap the plugs to the most common setting.
An incorrect spark plug gap can cause misfiring, poor fuel economy, a loss of power, and it can cause the plug to wear out faster.
Let’s not forget if you have made modifications to your engine. If yo’uve added a turbo or a high powered ignition system, you will need to use a different setting from the manufacturer’s recommendation.
Last, I don’t know about you, but after working for years in the parts department for aftermarket parts and even at dealers, spark plugs can take a beating. We drop them, sometimes drop them and step on them, toss the boxes around, and more. You get the picture.
While you might think that this won’t affect the gap, think again. Even the mechanics at every dealer I have ever worked for check the spark plug gap on new plugs. They know that the plugs gap may have been inadvertently altered in the shipping process.
This is why you should have the perfect spark plug gap tool. While all spark plug gap tools do basically the same thing, they aren’t all the same.
If you are curious about what differences there are between spark plug gap tools and which one is the best for you and your vehicles, keep reading.
I’ve done all the research for you.
How to gap spark plugs without a tool?
What would you do if you did not have any tool to set the gap on a set of spark plugs?
If you are a serious old-timer (like me) you might remember a time when the points on your car got so burned that the car wouldn’t start.
If you’re stranded in the middle of nowhere buying a new set wasn’t possible. Did you remove the points, sand down the burned part with whatever you could find (a nail file? a scrap of sandpaper?) and then use a matchbook cover to set them temporarily?
I clearly remember doing this more than once, but gapping spark plugs without any tools? Channel lock pliers may work well.
For the average car, a gap of .025 would work just fine until you could get a true reading from a trusty feeler gauge or other spark plug gap tool.
I’ve also seen my share of people use a flat head screwdriver to pry the electrode open.
This isn’t a good idea, again, because while the electrode looks thick, it isn’t that difficult to chip or to break it off entirely. (Yes, this is experience talking!)
Hopefully, you never find yourself in this situation, but I’ve been around, and I know that it happens.
How do you read a spark plug gap tool?
First, you will need to know what gap your engine uses. If you are new to this, you can start with the gap that the manufacturer recommends.
Older model cars might use SAE readings, which look like this: .025 or .030. Newer models will most likely list their numbers by metric readings, which look like this: 0.6 or 1.8, etc.
Many spark plug gap tools have measuring capabilities for both SAE and metric.
Let’s assume that you need to gap your spark plugs at .025. Find the feeler gauge with that number or find that number on whatever spark plug gap tool that you have.
Place the feeler gauge or other tool between the two electrodes. The tool should have a little bit of resistance when you try to insert it between the electrodes, as well as when you pull it out.
If the feeler gauge slides in with no resistance and you can see that it is not touching the electrodes, the gap is too large. Most feeler gauges and other tools have a small opening on the ends to both close and open the electrodes. It should look something like a miniature bottle opener.
If the feeler gauge won’t go between the two electrodes, the space between them needs to be opened. Use the tool on the spark plug gap tool to open the electrodes, but just a very tiny bit. You can always make the opening wider if it is still too small, right?
Continue until the space between the spark plugs is the perfect fit. A larger feeler gauge should not be able to fit between these two spaces. A smaller feeler gauge will have no resistance. The correct feeler gauge will have a slight amount of resistance when you place it between the two electrodes.
What is the correct spark plug gap?
Every engine has a different setting, much in the same way that every person has a different shoe size.
Not only does the year and engine model matter, but how you drive and how many miles you put on your car also matter.
You can always start with the manufacturer’s setting for the spark plug gap. In general, that will be somewhere between 0.6-1.8M or 0.024 and 0.071 SAE.
Your owner’s manual or repair manual can help you with this information, or you can search for it. You can also speak to a mechanic about what they feel would be the proper gap for the spark plugs on your vehicle. It will depend on its age and your driving habits.
What happens if the spark plug gap is too big?
For those who say that that spark plug gap isn’t really important, they might think otherwise when their car won’t start.
Yep, a spark plug gap that is very big or wide may cause the engine to not start at all! More common though, the engine will develop a misfire problem, where that cylinder doesn’t fire at all.
When the gap is too large, the voltage must travel too far. The farther the voltage must travel, the weaker the charge becomes. This can cause quite a variety of problems. That includes misfiring, fouled plugs, and engine hesitation. It can also cause a no-start or hard start problem.
Can spark plug gap cause rough idle?
Yes. An excessive or wide spark plug gap can cause a rough idle. It also won’t allow the car to start at all or cause it to run very rough because the cylinder doesn’t fire.
A gap that is too small can cause similar problems, including missing, hard starting, and a rough idle.
Do spark plug gaps increase over time?
Yes, the gap will increase over time.
The gap can increase due to the continual heating and cooling of the spark plug. The electrodes can begin to wear down during normal operation of sending very high voltage between the electrodes. This can lead to gap to increase.
While you might be able to reset the gap to its proper setting, the electrodes will wear down to the point of no return and they must be replaced.
Keeping the spark plugs on your ride properly gapped is what remains important in the long run.