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Most car makers use aluminum alloys inside the cylinder heads of most cars, so it’s very important to tighten spark plugs to the correct torque. If you overtighten spark plugs that have an aluminum cylinder head, it can cause the shell of the spark plug to distorts, which leaves you with a broken seal between the porcelain and metal components – leading to a combustion leak.
If you continue to work a spark plug after this happens, the contraction and expansion can cause the spark plug that is overtightened to come out from the cylinder head, threads included. If this happens, you’re looking at the cost of $500 to $1,000 for repairs.
However, if you under tighten a spark plug, that spark plug can come loose. When this happens, the high pressure that’s inside the combustion chamber can cause the spark plug to blow right out of the engine, taking with it the threads. In other words, you can cause substantial damage to your engine by overtightening or under-tightening your spark plugs.
You can’t perform guesswork with the amount of torque needed for spark plugs. Think of the costly repair work that would need to be done if you were to trust your gut on the correct torque of your spark plug. So, you should always use a torque wrench to find the correct torque for your spark plug.
What Torque Wrench Should I Buy?
The cheapest type of torque wrench is the beam style. They are also accurate throughout their rated range, but they can be hard to read if the spark plugs, you’re working on are located on the rear bank. You should purchase a beam style torque wrench if you’re installing spark plugs on the top of your engine or on a small engine and hope to save some money.
The second most affordable torque wrench is the click style. However, a click-style torque wrench is most accurate in the middle range of its rated torque. This means that since some recommended spark plug torques are as low as seven foot-pounds, and it can be hard to find a 3/8-inch drive torque that has seven foot-pounds in the middle range. This usually means that you’ll have to purchase an inch-pound torque wrench.
Converting Inch-Pound Readings to Foot-Pounds
If you’re working on a spark plug that has a recommended torque level in foot-pounds, but you’re using an inch-pound torque wrench, you need to know how to convert it to match the tool you’re using. To convert the foot-pounds to inch-pounds, all you need to do is multiply the foot-pounds recommendation by 12. So, if you’re working with a spark plug recommendation of 6 foot-pounds, it converts to 72 inch-pounds.
If the recommended toque is in inch-pounds, and you need to convert it to foot-pounds, all you need to do is divide the inch-pounds by 12. So, if you’re working with a spark plug that has a recommended 108 inch-pounds, that converts to 9 foot-pounds.
If you’re not sure about the specification that you need to tighten a spark plug, look at the chart below to help you figure it out.
When to Change Spark Plugs
How frequently should you change your spark plugs? Not every spark plug is rated for 150,000 miles; in fact, many car makers recommend changing spark plugs at intervals of 30,000-miles. So, you should always follow the recommendation that can be found in your owner’s manual.
If you don’t remember the last time you replaced your spark plugs, you can take them out and check their condition and gap. When you’ve put the labor in to check a spark plug, you might as well go ahead and change them to create a new baseline for future use.
It makes sense to replace your spark plugs early too. For instance, if you’ve got 60,000 miles on a set of 100,000-mile spark plugs, they’re already 60 percent worn and starting to take a toll on your engine’s performance and gas mileage. Perhaps the worst thing that can happen is that the amount of wear on the spark plug can cause it to seize in the cylinder head. Removing a seized spark plug is an expensive job, particularly if you the threads were damaged too.
So, what are the benefits of changing your spark plugs? When you think about the gas mileage falloff and the possibility of seized spark plugs, early replacement of your spark plugs makes sense.
Using a torque wrench to replace your spark plugs is very important. It helps prevent you from overtightening or under-tightening the spark plug, which can lead to stripped threads and the possibility of the spark plug popping out.
Torque wrenches come in a variety of sizes, so to know which one you should use for your spark plugs, it’s best to look at the user’s manual or the back of the spark plug pack to see if they tell you what torque to use. If they don’t, you can use the table we’ve provided above to figure out what you should use.
Remember that torque wrenches can come in inch-pounds, foot-pounds, or Newton-meters. If you need to convert from foot-pounds or inch-meters, all you need to do is multiply or divide by 12 to find the correct amount of torque you need.
Another thing that you should note is early replacement of your spark plugs. It’s best to replace your spark plugs before you need to make your engine run smoother and protect your car from having seized spark plugs – which can result in costly repairs.
No matter what you do, changing your spark plugs and using the right-sized torque wrench is essential. Hopefully, from this article, you’ve learned how to figure out what size torque wrench you need to change spark plugs, and also the importance of changing your spark plugs.