Spark plugs are an essential part of your car’s performance and health. These small but mighty plugs create a spark of electricity that puts the engine’s pistons in motion, which means they’re responsible for getting your car moving! Like all parts, spark plugs need to be tightened every so often, but do you need a torque wrench to do so?
You do not need a torque wrench to tighten spark plugs. However, it is sometimes useful to have a torque wrench for proper spark plug tightening, as it makes the task of tightening easier and quicker.
The rest of this article will answer your questions about spark plugs and torque wrenches. Additionally, it details how to tighten your spark plugs if you don’t have access to a torque wrench. If you want to ensure that your engine is running as it should, keep reading!
Quick Navigation
- What Size Torque Wrench For Spark Plugs?
- What Happens if You Don't Torque Spark Plugs?
- How Much Torque for Spark Plugs?
- Types of Torque Wrenches to Use for Spark Plugs
- How To Tighten Spark Plugs Without a Torque Wrench
- Conclusion
What Size Torque Wrench For Spark Plugs?
The best size torque wrench for spark plugs is a ½ inch (19 mm) wrench. This size wrench is capable of the most major and common repairs, so it is sufficient to meet your spark plug needs.
Torque wrenches are available at many price points and in socket-drive sizes of ¼, ⅜, ½, ¾, and 1 inch (11, 14, 19, 29 and 38 mm). The best size for a car owner to invest in is a ½ inch (19 mm).
Smaller torque wrenches, with socket-drive sizes of ¼ or ⅜ inch (11 mm or 14 mm), are used for delicate fixes and installations, such as a temperature switch. Bigger ones, with a socket-drive size of ¾ or 1 inch (29 mm or 38 mm), are for bigger twists on crank pulleys. A ½ inch (19 mm) torque wrench is ideal for spark plug tightening.
What Happens if You Don’t Torque Spark Plugs?
If you don’t torque spark plugs, they may be too tight or too loose, and you’ll experience various issues with your car. Your car may be unable to start.
If your spark plugs are too loose, the plug will not properly seal off the combustion chamber, and the cylinder compression will be lost. This means that there will be excess oxygen inside the cylinder, which causes many problems for the engine.
Here are some other issues that can arise from spark plugs that are too loose:
- Pre-ignition. Pre-ignition occurs when the fuel-air mixture in the engine ignites before the spark and causes the engine to continue running even after the ignition is turned off. Pre-ignition can melt or burn pistons.
- Piston damage. Piston failure causes the engine to suffer and reduces overall vehicle performance. If piston rings are worn out, they allow oil to leak into the combustion chamber and into the crankcase.
- Head gasket damage. A blown head gasket is bad news for your engine and causes overheating, loss of power, oil contamination, white smoke coming from the exhaust, and external leaks.
- Plug electrode damage. Damage to plug electrodes causes hard starts, decreased acceleration, and misfiring.
- Valve damage. Damage to the valves in your engine can cause reduced power and poor fuel consumption and can even lead to your engine’s complete failure. Incorrectly tightened spark plugs can cause burnt valves.
- Misfiring. If your engine momentarily stumbles, it is certainly a nuisance, but it is also an indicator of larger problems.
You also want to avoid over-tightening your spark plugs. If your spark plugs are too tight, the following problems can occur:
- Damage to the cylinder head bolts. This damage can cause oil and coolant to mix, oxygen to leak into places it shouldn’t be, and lost compression and condensation.
- The plug itself cracks or breaks. Too much tightening can stretch the metallic shell of the plug and cause it to break, and as the plug is an essential part of your engine’s health, this would be bad news.
- Damage to the spark plug thread. The only way to fix this issue is to get an expensive repair.
- Reduced RPM. Low RPMs can cause your engine to have a gearing disadvantage.
Either way, not torquing your spark plugs, or torquing them too much, will cause further problems with your car and will most likely lead to an expensive trip to the mechanic.
How Much Torque for Spark Plugs?
How much torque your spark plugs need ranges from 8 to 38 lbs-ft (10.8 to 52.9 Nm). The variables that influence the amount of torque include the seat type, thread size, and the material of the cylinder head.
There are two kinds of spark plug seats: flat and tapered. Flat seat plugs have a crushable gasket that acts as the seal between the plug and the combustion chamber. Tapered seat plugs use the outer shell of the spark plug itself as the seal.
Torque is measured in pounds-feet. This is a force in pounds acting on a lever measured in feet.
Here is a general guide for how much torque to apply to spark plugs:
| Seat Type | Thread Size | Torque (Aluminum) | Torque (Cast Iron) |
| Flat | 10 mm (0.39 in) | 8-12 lb. ft. (10.8-16.3 N. m.) | 8-12 lb. ft. (10.8-16.3 N. m.) |
| Flat | 12 mm (0.47 in) | 10-18 lb. ft. (13.6-24.4 N. m.) | 10-18 lb. ft. (13.6-24.4 N. m.) |
| Flat | 14 mm (0.55 in) | 18-22 lb. ft. (24.4-2.8 N. m.) | 26-30 lb. ft. (35.3-40.7 N. m.) |
| Flat | 18 mm (0.71 in) | 28-34 lb. ft. (38-46.1 N.m.) | 32-38 lb. ft. (32.4-52.9 N. m.) |
| Tapered | 14 mm (0.55 in) | 7-15 lb. ft. (9.5-20.3 N. m.) | 7-15 lb. ft. (9.5-20.3 N. m.) |
| Tapered | 18 mm (0.71 in) | 15-20 lb. ft. (20.3-27.1 N. m.) | 15-20 lb. ft. (20.3-27.1 N. m.) |
You should always follow your car manufacturer’s recommendation.
Types of Torque Wrenches to Use for Spark Plugs
A torque wrench is an advantageous tool for the proper tightening of spark plugs, but it is unnecessary. You can tighten your spark plugs without one as long as you follow the manufacturer’s instructions.
A torque wrench is a tool that prevents the over-tightening of spark plugs, as well as screws, nuts, and bolts. John H. Sharp designed it in 1931, and it has been used to tighten spark plugs since its invention. A torque wrench differs from a basic wrench because it indicates how much force is applied through an electronic window, a click, a needle, or a gauge.
There are four kinds of torque wrenches:
- Electronic or digital
- Beam or deflection
- Dial
- Clicker
Here is a guide to types of torque wrenches and how they work, as well as my recommendation for a good wrench of that type:
| Type of Torque Wrench | How It Works | Product Recommendation |
| Electronic or Digital | Digital wrenches work from an electric sensor and inform the user how much force is applied with a digital display. It is easy to set a torque limit with this wrench. To use it, turn on the wrench, set the torque using the arrows, place the wrench on the plug, and adjust the angle up and down until you’ve reached the torque measurement. | I recommend eTork ½ inch Electronic Torque Wrench from Amazon. This electronic wrench has a Certificate of Calibration that ensures accuracy. Furthermore, the early-alert function, red LED light, and buzzer indicator ensure that you know when you’ve reached your target torque. |
| Beam or deflection | This affordable wrench has a scale, and once you’ve reached the desired level of torque, the scale stops. The main beam has a handle that you use to apply the force. | For a beam wrench, I like the TOOLUXE Beam Style Torque Wrench available on Amazon. This wrench has a powerful steel alloy and a durable finish that ensures it will last a long time, so you get a better bang for your buck. It also has a graduated tip, which prevents parallax error. |
| Dial | These wrenches are considered the most accurate, but they are wider than other kinds, so they may be more difficult to use in tight spaces. The dial has two meters (6.5 ft). One moves according to the applied torque, and the other sets where you’ve stopped applying force. | I recommend the CDI Drive Dial Torque Wrench on Amazon because it has a sturdy torsion beam that ensures accuracy and longevity. It also has a wide torque range, from 0 to 175 ft. lbs (238 N-m). |
| Clicker | This wrench gives an audible “click” sound when the right torque has been reached. This occurs because a spring-loaded lever breaks and makes the noise. The lever is adjusted when the handle is twisted. | The LEXIVON Click Type Torque Wrench from Amazon ships pre-calibrated for your convenience and has a reinforced ratchet gear head, so it will last you a long time. Its highlighted dual-range scale is easy to read, so you can identify your torque level even in low-light conditions (like your dark garage)! |
All of these types of torque wrenches are designed to prevent over-tightening, and they are adjustable, which allows you to preset the torque measurement. Once this torque level is met, the wrench will stop tightening, so you can rest assured that your spark plugs are at the right level of torque and not over-tightened.
You should always tighten your spark plugs according to the manufacturer’s instructions, so using a torque wrench is a good way to accomplish this with accuracy and precision. However, there are other ways to tighten your spark plugs properly without using this tool.
How To Tighten Spark Plugs Without a Torque Wrench
It is possible to tighten spark plugs without using a torque wrench, but you’ll be adjusting by feeling instead of accurate measurement.
One way to tighten spark plugs is to hand-tighten them. You may not be able to get enough force to get your spark plugs tight enough, but it is an option. You can also hand-tighten your spark plugs first before using a torque wrench to tighten them.
To hand-tighten flat or gasket plugs, screw them into a cold engine with your hand until they seat, and then use a ratchet and a socket to tighten the plugs a half turn.
For tapered plugs, you can also tighten the plugs with your hand until they seat, and then use your socket and ratchet to tighten them a quarter turn further.
The following video demonstrates how to change spark plugs with or without torque wrench:
With this method, you are relying largely on the “feel” and if the spark plugs feel tight enough. Experienced mechanics can do this pretty easily because they have practice, but it could be difficult to determine whether you’ve tightened the spark plugs enough or too much if you are a novice.
This method also varies by person, depending on their strength. Most importantly, avoid stripping out the spark plug threads.
Conclusion
It is essential for your car engine’s health and functionality that the spark plugs are properly tightened according to the manufacturer’s instructions.
A torque wrench is a great tool to use to accomplish this with accuracy, and it makes the task of tightening quicker and easier. However, it is not necessary to have a torque wrench. It is possible to tighten your spark plugs properly without one.
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