how much tight to tighten spark plugs have to be

how much tight to tighten spark plugs

Spark plugs are very important since they’re the one that starts the ignition of the engine so a vehicle like a car can start running.

According to experts, sparkplugs are tightened between 8-40nm (nanometer) and should be installed according to the manufacturer’s recommendation.

It’s important to have the spark plug be in the right torque and carefully installed because it has a very important role to play in an engine.

How Tight Should Spark Plugs Be? The Correct Measurement

As seen by Philipps Vision’s YouTube video, if it’s too loose, it can cause:

  • Misfires
  • Performance Issues

And on the other hand, he said that if it was over-tightened, you’ll end up

  • Stripping the thread
  • Cause damage
  • It’ll be harder to retrieve if they break

That’s why he mentions that you need to tighten them with the proper spec and with the proper torque perfectly, so that you get the best performance from it in your vehicle.

In the past, cars had iron cylinders where you can install plugs by turning them by hand with new copper washers.

After they were installed, you could turn them with a plug wrench until they felt resistance, you then twist the plugs an additional ¼ to ½ turn to compress the copper washer.

With today’s car technology, cars have aluminum cylinder heads which is better than the copper version in the past.

Overturning or tightening the spark plug too much in an aluminum cylinder head can entirely damage the spark plug thread, requiring an entire spark plug replacement.

So, the best solution to avoid this (overturning the spark plug) is to follow the recommended torque mentioned by your manufacturer.

According to ngksparkplugs, torque is one of the most critical aspects of spark plug installation.

Torque directly affects the ability of the spark plug firing end to dissipate heat to the cylinder head.

Here’s a table that they have provided so that it will be easier for us to have a general understanding of the torque with the thread diameter specs and spark plug type:

Spark Plug Type Thread Diameter Cast Iron Cylinder Aluminum Cylinder
Flat seat type (with gasket) 18 ø mm 25.3 ~ 32.5 25.3 ~ 32.5
Flat seat type (with gasket) 14 ø mm 25.3 ~ 32.5 18.0 ~ 21.6
Flat seat type (with gasket) 12 ø mm 10.8 ~ 18.0 10.8 ~ 14.5
Flat seat type (with gasket) 10 ø mm 7.2 ~ 10.8 7.2 ~ 8.7
Flat seat type (with gasket) 8 ø mm 5.8 ~ 7.2
Conical seat type (without gasket) 18 ø mm 14.5 ~ 21.6 14.5 ~ 21.6
Conical seat type (without gasket) 14 ø mm 10.8~18.0 7.2 ~ 14.5
Conical seat type (without gasket) 12 ø mm 7.36 ~ 14.75

We still recommend you check your manufacturer’s recommendation because they are going to have the perfect measurement for the torque details you need.

Use the table above as a mild guide on the torque instructions with the spark plugs, whether you have a cast-iron cylinder or an aluminum cylinder, it can be found on the table above.

Avoid over-torquing at all costs, it can cause the metal shell of the plug to stretch, the threads can also crack and/or break off.

What Happens When Spark Plugs Are Too Loose?

If the spark plugs are loose, the vibrations aren’t absorbed. Moreover, if it’s loose, it’s going to be looser with more distance, affecting the performance of the cylinder.

You also run the risk of having a high-temperature combustion gasses leak, it will leak pass the plug and melt the thread.

What Happens If Spark Plugs Are Too Tight?

If the spark plug gets broken, it’ll be harder for you to remove it and might even end up damaging the bolt hole.

A damaged bolt hole is not going to allow you to install a new spark plug and will even cost you more on repairs. It can also damage the thread, this means you have to replace the spark plug.

How Do I Know If My Spark Plugs Are Too Tight Or Too Loose?

Try twisting the spark plugs, unless you already have them checked out in a car shop, then try twisting it.

According to repairsmith, if you can easily turn it around, then it’s loose, if you can’t turn it around with a wrench then it’s too tight.

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