LS Exhaust Manifold Bolt Torque (Everything You Need To Know)

LS exhaust manifold bolt torque is a crucial factor to consider while tightening the bolts. Too much torque leads to bolt snapping or breakage of the cast iron, while less-torque leaves gaps for exhaust gas leakage. Therefore, there is a need to establish the correct torque and sequence for tightening the bolts.

So what is the required torque for LS exhaust manifold bolts? It has two stages of tightening. Start with 11-12 ft-lbs. for the first stage in sequence, then follow 18-20 ft-lbs. in the final stage to firmly hold the exhaust manifold. Thus, begin with two bolts from the center, alternate from side to side, and work toward the outside bolts for the sequence.

In this article, we shall look at the appropriate LS exhaust manifold bolt torque and the sequence to avoid damaging the exhaust manifold and the cast iron. Read on for more information!

LS Exhaust Manifold Bolt Torque: Quick Overview

Below is the data for the required torque for the LS exhaust manifold bolt type. Read through this table if you are in a hurry to read the full article.

Exhaust manifold bolt type Required torque
Exhaust Manifold Bolts-First step 11-12 ft lb.
Exhaust Manifold Bolts-Final step 18-20 ft lb.
Exhaust Manifold For Heat Shield Bolts 80-82 in lb.
Exhaust Manifold For Pipe Nuts 25-30 ft lb.

As noted above, each bolt has different torque requirements based on the expected pressure from the exhaust gasses. However, do not apply excess torque. It will break the bolt head or snap the cast iron block.

LS Exhaust Manifold Bolt Torque And Sequence

Bolt torque is a susceptible aspects while tightening the exhaust manifold bolts. This has to be done sequentially to avoid leakages by tightening the exhaust manifold bolts beginning with the center two bolts. You then alternate from side to side and work toward the outside bolts.

However, some people opt to start from bolt number one to the last bolt. This technique works but only applies when tightening reused bolts that have lost the thread set.

This sequence ensures tight and balanced torque distribution. It also avoids breaking and snapping the bolts. The bolts are four in number and are not to be tightened at once. The tightening is done in two steps using a hand torque wrench.

First Pass

After inserting the bolts into the respective holes, use a hand torque wrench to tighten them into the first pass torque. Tighten them to 11 ft-lbs in sequential order. Some may opt to tighten up to 12 ft-lbs. Both are acceptable as the bolts will undergo further tightening.

Final Pass

Following the same sequence, tighten the bolts to 18 ft-lbs. Use the hand torque wrench and ensure the bolts are tightened to torque. During this final pass, the bolts straighten and become lock-tight.

It’s for the same reason that they can only be used once. Thus, the LS exhaust manifold bolt torque should be maintained equal for all bolts for a tight fit to ensure exhaust gasses do not leak.

Shield bolts and Pipe nuts

The shield and pipe are fastened to a different torque for maximum tightness.

Shield bolts are fastened to a torque of 80 lb. Pipe nuts are tightened to a torque of 26-30 ft-lbs.

Why Do LS Exhaust Manifold Bolts Break While Removing?

Exhaust manifold bolts are a one-time use bolt. What does it mean to be a one-time usage bolt?

Usually, the original bolts are designed with distorted threads, and the threads straighten upon fastening to cause a good locking effect. These twisting threads lock in such a way that makes it hard to unscrew and use them again.

However, you can reuse them, but with less efficiency. The flat washers on the bolt heads make it hard to unscrew, and the bolts snap if excessive force is applied. Thus, an exhaust manifold with a reused bolt may leak exhaust gasses. Hence, we wouldn’t recommend reusing these bolts for high-power LS engines.

How To Remove LS Exhaust Manifold Bolts Without Breaking Them

Most mechanics find it hard to remove the LS exhaust manifold bolts. Due to pressure from the bolt torque, removing the bolts causes them to break. Care is needed when unscrewing the bolts.

Two methods guarantee a smooth removal process: the heating method and the loosening and re-tightening method. You require the following tools for an easy task.

1. Heating Method

The heating method requires one to heat the bolt head for about two minutes. Allow the bolt to cool down, and then use the hand torque wrench to twist it open.

So the principle behind the heating method is the expansion and contraction of the bolt and the bolt hole. When heated, the bolt hole expands as the bolt expands. On cooling, the bolt, a steel material, cools faster than the cast iron block.

This uneven cooling helps lose the lock-tight threads. A simple twist with the wrench breaks the thread rust making it easy to open.

2. Re-Tightening Method

This method uses penetrating oil to soften the threads holding the bolt. Apply the oil at least 12 hours before opening. The oil penetrates through the threads, making it easier to unscrew the bolts.

Use the technique of loosening and re-tightening the bolt to break loose the holding threads.

Both methods use the reverse torque sequence to loosen the bolts to avoid breaking or snapping their bolts.

Conclusion

The LS exhaust manifold bolt torque should be maintained at 11 ft-lbs. for the first pass and then tightened to 18 ft-lbs. While tightening, follow the sequence starting with the two center bolts and then alternating side-to-side while working towards the outside.

And when tightening the bolts, use a hand torque wrench to avoid exerting extreme torque that would otherwise break the bolts. Use star-shaped washers for a better grip. Also, avoid open flat washers as they slide while unscrewing.

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