LS Flywheel Bolt Torque Specs and Sequence

We can look at the flywheel as a giant rotating weight that absorbs the engine vibrations, preventing them from being transferred into the cabin. But even more crucially, the flywheel lowers the crankshaft and piston vibration, which is why it’s critical to torque it down properly to prevent the bolts from backing out, thus destroying both the engine and the transmission. So, here is what the torque specs are in an LS engine.

The LS flywheel bolt torque specs are separated into a couple of stages. In the third-generation LS and some fourth-generation ones, the first pass is 15 lb-ft, the second pass is 35 lb-ft, and the third and final torque spec is 74 lb-ft. In most versions of the fourth generation LS, the first pass is 22 lb-ft; after that, you turn the wrench another 40°, and that’s it.

LS Flywheel Bolt Torque Explained

All car engines have flywheel torque specs, but rarely are they ever as important as they are in LS engines. All LS engines have a cross-plane crankshaft which, by design, creates a lot of vibrations and powerful pulses going through the crankshaft. Then, considering that some LS engines have a displacement of up to 7.0 liters, it’s easy to see how flywheel vibrations can be a problem.

If the LS flywheel bolt torque is incorrect, they are more likely than not to back out and fly into the clutch assembly and end up destroying it. But keep driving for a while, and all the extra vibrations can destroy the rod bearings and transmission bearings, so it’s not worth the risk. Also, before you jump into the LS torque specs below and beginning looking for your car or engine, pay attention to the following instructions.

LS Engine “15 > 37 > 74 lb-ft” Flywheel Bolt Torque Pattern Explained

With the bolt pattern in question, each of the numbers represents a torque spec, so that’s 15 lb-ft, 37 lb-ft, and 74 lb-ft. The reason there are three different specs is that you first have to tighten all the bolts to 15 lb-ft (first pass), then again to 37 lb-ft (second pass), and finally 74 lb-ft (third pass). The LS 5.3 flywheel torque specs are the same.

The reason this is important is to tighten the flywheel as evenly as possible all around. In other words, you need to do all three passes to prevent the flywheel metal from compressing under the bolts unequally.

If you fail to do this, the flywheel metal will be more compressed under the last couple of bolts you tightened. In other words, that means the first couple of bolts you tightened will become loose and not to spec by the time you tighten the rest of them.

Also, for all LS engines with the “15>37>74” bolt pattern, GM recommends putting just a smear of blue thread locker on each bolt. Now, some people argue against this, but in the case of this pattern that doesn’t have TTY (torque to yield) bolts, we would say that GM’s recommendation makes more sense.

LS Engine “22 lb-ft + 40° (TTY)” Flywheel Bolt Torque Pattern Explained

The “22 lb-ft + 40°” bolt pattern may not make a lot of sense initially, but once we understand what torque to yield (TTY) means, it will be clear as day. Torque to yield means the bolt is designed to stretch to a certain length as it’s tightened to the required torque spec.

That means once the bolt has been stretched, it cannot be reused because if you tighten it to the same spec again, it won’t be tight enough because it’s already stretched. However, if you tighten it so that it stretches again, it will lose almost all its tensile strength, and it’s only a matter of time before it snaps. So, again, every time you remove TTY bolts, you have to replace them.

Now, how does the pattern work? The pattern at hand is divided into two passes. In the first pass, you tighten all the flywheel bolts to 22 lb-ft. After that, you turn each bolt for another 40 degrees, and if at all possible, you do it in one swing instead of going 20°+20° or any similar pattern.

To turn all the bolts exactly 40°, you need a degree torque wrench or a torque wrench degree gauge tool that fits over your standard torque wrench. But before you go out and buy a new one, check whether your torque wrench already has a degree setting because most modern ones do.

Third Generation LS Flywheel Torque Specs (1999-2007)

The third-generation LS engine is actually the first generation. The reason these are called third is all of them are based on the third-generation Chevy small block V8. The third generation only saw two versions of the engine, the LS1, and LS6 making it super simple to find your vehicle in the list below.

LS1

Flywheel Torque Specs – 15 > 37 > 74 lb-ft

Vehicles With the LS1 Engine

LS6

Flywheel Torque Specs – 15 > 37 > 74 lb-ft

Vehicles With the LS6 Engine

Fourth Generation LS Flywheel Torque Specs (2005-2020)

The fourth generation LS engines have a two-year production overlap with the third generation, so make sure you find your vehicle by name and model year instead of going by the generations only. Especially if you suspect you have a fourth-generation LS because not all of them have the same flywheel torque specs.

LS2 

Flywheel Torque Specs – 22 lb-ft + 40° (TTY)

Vehicles With the LS2 Engine

LS3

Flywheel Torque Specs – 22 lb-ft + 40° (TTY)

Vehicles With the LS3 Engine

LS4

Flywheel Torque Specs – No Flywheel (Automatic Transmission Only)

Vehicles With the LS4 Engine

LS7

Flywheel Torque Specs – 15 > 37 > 74 lb-ft

Vehicles With the LS7 Engine

LS9

Flywheel Torque Specs – 15 > 37 > 74 lb-ft

Vehicles With the LS9 Engine

LSA

Flywheel Torque Specs – 15 > 37 > 74 lb-ft

Vehicles With the LSA Engine

FAQs:

Q: What should flywheel bolts be torqued to?

The flywheel bolts should be torqued to anywhere between 60 lb-ft and 80 lb-ft, depending on the engine. But it’s important that you find the correct torque specs for your specific engine and tighten the bolts accordingly.

Q: What is the torque on flex plate bolts?

The flex plate bolts on an LS engine are the same as it is on the flywheel, and that’s 74 lb-ft. However, you should do it in the three-pass sequence that looks like this: 15 > 37 > 74 lb-ft.

Q: Is it necessary to torque a flywheel?

Yes, it’s necessary to torque a flywheel because there are no washers between the flywheel and the crankshaft. That means the bolts need to be stretched out to a specific length to secure the flywheel, which can only be achieved by tightening them to the manufacturer’s recommended torque.

Q: Do you lose torque with a lighter flywheel?

No, you do not lose torque with a lighter flywheel. On the contrary, you will gain both torque and horsepower with a lighter flywheel because the engine has less parasitic weight. However, the engine does lose some momentum, making it harder to spin the wheels with a clutch kick.

Q: What is the bolt thread pitch on an LS flex plate?

The bolt thread pitch on an LS flex plate is 1.5. The bolts are 11mm in diameter and are grade 8 steel. You can also find stronger aftermarket 12.9-grade bolts for an LS flex plate.

Final Words

To summarize, the LS1, LS6, LS7, LS9, and LSA engines all have a 74 lb-ft torque spec for the flywheel bolts. Also, the sequence in which you tighten them is a three-pass and is as follows: 15 > 37 > 74 lb-ft.

The remaining LS2 and LS3 engines have a TTY (torque to yield) flywheel torque spec, which is 22 lb-ft + 40°. That means tightening all bolts to 22 lb-ft and then tightening them another 40 degrees. And lastly, the LS4 engine never had a manual transmission which means it doesn’t have a flywheel.