In most LS engines, getting the right torque for the LS flexplate bolt is super essential. If it’s not done correctly, it can cause problems related to vibrations or even transmission failure.
Let’s discover the LS flexplate bolt torque to learn why it is so important. Besides, we’ll give you easy-to-follow tips on how to remove and tighten them properly. Let’s dive in for more details.
What Is Flexplate Bolt Torque?
Flexplate bolt torque is the specific amount of tightening force applied to the bolt heads that attach the flexplate to the engine’s crankshaft.
It’s important to tighten these couple of bolts according to the manufacturer’s recommended specifications.
This way, the flexplate stays firmly connected to the crankshaft and efficiently transfers engine power to the automatic transmission’s torque converter.
Proper flex plate bolt torque prevents problems like misalignment and vibrations and keeps the transmission safe.
It ensures the engine and the transmission work smoothly, making your vehicle perform better and last longer.
What Are The LS Flexplate Bolt Torque Specs?
The LS flexplate torque specs vary based on the LS generations. For the third-generation LS engine, the torque has three passes: 15 lb-ft, 37 lb-ft, and 74 lb-ft. For most fourth-gen, the torque is 22 lb-ft.
LS Flexplate Bolt Torque And Size
The LS flex plate torque/ flywheel bolt torque specs vary depending on the engine generation and design.
In the third-generation LS and some fourth-generation LS engines, the tightening process involves multiple stages:
- First pass: 15 lb-ft
- Second pass: 35 lb-ft
- Third pass (final torque): 74 lb-ft
In most versions of the fourth-generation LS engines, the LS flywheel bolt torque process is as follows:
- First pass: 22 lb-ft
- Then, turn the wrench another 40°
The LS flexplate bolt has a 12-point socket with a size of 3/4 inches.
The thread size of the bolt is M11 x 1.5, which means it has an 11-millimeter diameter with a 1.5-millimeter distance between threads.
Why Is LS Flexplate Bolt Torque Important?
LS flywheel torque specs are crucial for LS engines because they have strong vibrations due to their crankshaft design.
Correct torque prevents bolts from coming loose, which could damage the clutch and lead to transmission issues.
It also protects rod bearings and the transmission from excessive vibrations.
Proper torque ensures safety, reliability, and even compression, preventing bolt failures and maintaining drivetrain integrity.
Following the manufacturer’s flexplate guide is essential for avoiding costly damage and keeping the vehicle running smoothly.
Never underestimate the importance of proper flexplate bolt torque in LS engines.
How To Remove And Install LS Flexplate Bolt Properly?
Necessary tools:
- Torque wrench
- Socket set
- Loctite
- A degree torque wrench or gauge tool (for Fourth-Generation LS)
Third-Generation LS
Step 1: Preparation
- Disconnect the car battery to prevent electrical accidents.
- Raise the vehicle and secure it with jack stands for safety and better access to the flexplate area.
- Remove the transmission to access the flex plate if it is still attached.
Step 2: Locate the flexplate and bolts
- The flexplate is placed between the engine’s crankshaft and the torque converter.
- Identify the flexplate bolts, typically six in number, surrounding the flexplate’s center hole.
Step 3: Remove old bolts
- Use a socket wrench to remove each flexplate bolt one by one.
- Ensure the bolts are not damaged during removal.
Step 4: Clean bolt threads and holes
Clean the bolt threads and holes in the cross-plane crankshaft thoroughly to remove any debris or residue.
Step 5: Tighten bolts in sequence
Use a torque wrench in a criss-cross or star pattern to ensure even compression:
- Start with the first pass: Tighten each bolt to 15 lb-ft
- Move on to the second pass: Fasten the bolt to 37 lb-ft
- Finally, the third pass: Wrench the bolt to 74 lb-ft
Fourth-Third-Generation LS
Step 1: Preparation
- As in the third-generation LS, disconnect the negative battery terminal and raise the vehicle on jack stands for safety.
- Just like before, remove the transmission to access the flexplate.
Step 2: Align flexplate
- Align the extra hole (if present) on the LS crank with the empty spot on the flexplate.
- Clean the bolt threads, holes, and flush the torque converter if necessary.
Step 3: Apply Loctite
Apply Loctite to the threads of each bolt before reinstalling.
Step 4: Tighten bolts in two passes
- First pass: Tighten all bolts to 22 lb-ft in a criss-cross.
- Second pass: Use a degree torque wrench or gauge tool to turn each bolt an additional 40 degrees, preferably in one swing, for uniformity.
Step 5: Reinstall the transmission
If you removed the transmission, reattach it, ensuring proper alignment and secure mounting.
Is The LS Swap Possible?
How To Differentiate LS Flexplate?
- Identify the LS engine: Like a swap engine, you need to determine which LS engine variant you have, such as 4.8 LS, 5.3 LS, 5.7 LS, 6.0 LS, 6.2 LS, or 7.0 LS.
- Count the teeth: The major difference between the flexplate and other traditional plates is the flexplate’s tooth count. LS engines use a larger 168-tooth flexplate. Count the teeth on the flex plate to ensure it matches the 168 tooth pattern.
- Check for dual pattern: Some LS flexplates offer dual torque converter bolt patterns. Ensure your flexplate has both torque converter bolt patterns, allowing compatibility with numerous GM transmissions.
- Match transmission type: Ensure the flexplate option is compatible with your transmission type (e.g., 4L60E, 4L80E) to ensure proper fitment.
How To Swap LS Flexplate?
To swap the LS flexplate, follow these steps:
- Like engine swaps, you need to check which transmission you’ll use and make sure it works with your flex plate.
- Get the right components for your setup, like a dual pattern flexplate or a spacer.
- Disconnect the car battery for safety.
- Find the flexplate connected to the crankshaft at the back of the engine.
- Remove the bolts holding the old flexplate in place.
- Put the new flexplate on the crankshaft, aligning it correctly with any special patterns or spacers.
- Tighten the bolts gradually and evenly in the proper order, following the recommended flexplate torque specs.
- Reinstall the transmission if you took it out earlier.
- Reconnect the car battery.
- Start the engine and check for any strange noises or engine vibrations.
Note: Older GM transmissions (Powerglide, TH350, 700R4) have a different torque converter bolt pattern (10.75 inches).
You need a special flexplate and a torque hub adapter sleeve to use with an LS4 engine, LSA engine, or any series engines.
There’s a conversion kit available for this purpose, making the process easier.
FAQs
What Are BBC Flexplate Torque Specs?
The torque specification for flywheel/flexplate bolts on Big Block Chevy (BBC) engines is 60 ft.-lbs.
It’s best to tighten the bolts to this specification to ensure proper installation and prevent any potential issues with the flywheel or flexplate.
Can I Reuse The Flexplate Bolts When Reinstalling Or Replacing The Flexplate?
Yes, you can sometimes reuse the flexplate bolts when reinstalling or replacing the flexplate.
However, it’s important to check the bolts for damage and ensure they are tightened properly.
Should the bolts look good and are within the recommended limits, you can use them again.
But it’s safer to follow the manufacturer’s advice. If they suggest using new bolts, it’s better to do so to avoid any potential problems.
Always prioritize safety and check the bolts carefully before deciding whether to reuse them or get new ones.
What Happens If I Over-Torque Or Under-Torque The Flexplate Bolts?
If you tighten the flexplate bolts too much, they can stretch or deform. It can weaken the bolts, making them more prone to breaking or coming loose while the engine runs.
Over-torquing can also damage the flexplate or other connected components, leading to costly repairs.
On the other hand, if you don’t tighten the flexplate bolts enough, they may not provide sufficient clamping force. It can cause the bolts to gradually come loose over time, leading to vibrations and noise during engine operation.
Loose bolts also take a toll on the flexplate or other drivetrain components.
Conclusion
In conclusion, the 3rd generation LS flexplate bolt torque (Gen III, 1999-2007) is 15 lb-ft, 37 lb-ft, and 74 lb-ft.
The specs for flexplate bolts of most 4th generation (Gen IV, 2005-present) is 22 lb-ft.
Getting the right tightness is crucial to avoid bolt failures, keep the engine balanced, and prevent damage.
Consider replacing old or worn bolts instead of reusing them when installing or changing the flex plate.
Regularly check and maintain the flexplate bolts to ensure a safer, more reliable, smoother driving experience with LS engines.