Everything You Need to Know About 2-Bolt Main Studs

Strength and reliability are paramount in constructing a high-performance engine to produce maximum power and longevity. One of the most essential components contributing to this is the 2-bolt Main Stud. Engine builders and enthusiasts both tend to use 2-bolt main studs for their capability to firmly secure the crankshaft without allowing block distortion and to improve overall engine performance.

But what are 2-bolt main studs, and why are they so crucial to the longevity of your engine? In this definitive guide, we’ll explore everything you need to know about 2-bolt main studs, including their purpose and advantages, installation advice, and essential factors to consider. Whether you’re an experienced engine builder or a home mechanic, knowing the function of main studs is crucial for assembling a strong and high-performance engine.

What is a 2-Bolt Main Stud?

A 2-bolt main stud is vital in the engine block to hold the main bearings and crankshaft in position. Engine blocks usually incorporate main caps bolted onto the block using either 2-bolt or 4-bolt designs. The “2-bolt” indicates the quantity of bolts that hold each main cap to the block. In such a scenario, two bolts or studs are applied per main cap, holding the crankshaft and keeping it from moving under high RPM or high-stress operation.

Main studs, including 2-bolt types, are more prevalent in high-performance engines since they create a tighter and more solid grip than standard bolts. These studs are constructed using high-strength material, typically steel, to withstand the heavy pressure and vibrations generated during engine functioning.

In contrast to standard bolts, which may stretch or become distorted when subjected to high stress, main studs provide better clamping force and avoid loosening the main cap, keeping the crankshaft stable. This is critical in sustaining engine performance, durability, and reliability, particularly in modified or performance-built engines. While 4-bolt configurations are typically employed for even more strength, 2-bolt main studs balance performance and affordability for most engine applications.

How Does 2-Bolt Main Studs Work?

2-bolt main studs function as follows: The main caps are held to the engine block by the main studs, typically high-strength steel, keeping the crankshaft in place and preventing it from moving while in motion. The studs are designed to support the engine’s heavy crank load. This is a step-by-step examination of their process:

1. Main Caps and Engine Block

The engine block contains machined recesses or pockets for the main caps (the pieces that bear the crankshaft). The main caps rest on top of the lower half of the engine block and are centered over the crankshaft’s journals (the spinning shafts that connect to the pistons).

2. Studs vs. Bolts

In the 2-bolt form, two studs are threaded into the block, one in each of the two bolt holes on each main cap. These studs replace the standard bolts that would otherwise be used. The studs offer a more trustworthy, solid hold since they don’t stretch as bolts can when subjected to stress.

3. Securing the Crankshaft

After the main caps are installed and aligned with the crankshaft, the 2-bolt main studs are torqued into the engine block. Properly torqued, these studs provide a clamping force to hold the main caps against the engine block with assurance that the crankshaft will not shift away.

4. Prevention of Main Cap Movement

The major role of the 2-bolt main studs is to prevent the main cap from shifting or being lifted from the block when the engine experiences high-stress conditions like high RPM or load. This helps ensure that the crankshaft remains aligned and minimizes the possibility of engine damage due to cap failure or warpage.

5. Stronger and More Reliable

Studs are better than bolts since they are less subject to deformation when under pressure. The stud is initially driven into the block, and the principal cap is fitted over it. Securing the nut over the stud exerts a clamping force without threatening the block’s threads for stretching, which is an issue with the bolts that thread directly into the block.

6. Better Torque Retention

Since the threads on the stud are not elongated, the torque on the nut is more stable and dependable. It keeps the main cap tightly held during the engine’s operation, preventing crankshaft stability, block distortion, or cap movement issues.

Models that Use 2-Bolt Main Studs (Powerstroke, Duramax, Cummins)

For heavy-duty diesel engines such as Powerstroke, Duramax, and Cummins, the majority of these engines are engineered with heavy-duty use in mind and typically utilize more durable configurations, such as 4-bolt main studs, to deal with the incredible torque and stress they generate. Still, there are specific applications or setups where 2-bolt main studs can be employed, even if only for non-racing or lighter-duty applications, in cases where a vehicle does not require the superior endurance of a 4-bolt main setup. Below is a summary of such diesel engine types and whether or not they are compatible with 2-bolt main studs:

1. Ford Powerstroke Engines

Ford 7.3L Powerstroke (Early Models)
The 7.3L Powerstroke used in Ford Super Duty trucks (late 1990s to early 2000s) originally came with 2-bolt main caps. In most performance or stock rebuilds, 2-bolt main studs are utilized for added strength and reliability without going to 4-bolt main studs.

Ford 6.0L Powerstroke
The 6.0L Powerstroke of the early 2000 Ford trucks featured 2-bolt main caps from the factory. Moving to 2-bolt main studs is standard for rebuilding the engine or adding power, particularly on applications where extreme stress is not encountered (such as in everyday driving or light towing).

Ford 6.4L Powerstroke
The 6.4L Powerstroke also employed 2-bolt main caps in its construction, although, as with other Powerstroke engines, many high-performance builders and rebuilders replace main studs for increased strength. The 2-bolt main stud conversion is occasionally utilized in standard or stock overhauls.

2. Chevrolet Duramax Engines

Duramax 6.6L LB7 / LLY / LBZ
Early Duramax diesel engines (LB7, LLY, LBZ) originally had 2-bolt main caps, and numerous aftermarket manufacturers produced 2-bolt main studs for those engines. In most street or towing uses, 2-bolt main studs have sufficient strength and clamping pressure, but high-performance applications can move to 4-bolt main studs for increased durability.

Duramax 6.6L LMM / LML
The subsequent generations, such as the LMM and LML Duramax engines, tend to have more robust configurations. Though they might include 2-bolt main caps, performance drivers might install 2-bolt main studs for street or light performance use upon rebuilding. However, 4-bolt main configurations are the choice for high-stress use, such as racing or heavy hauling.

3. Cummins Diesel Engines

Cummins 5.9L (Early Models)
The earlier models of the Cummins 5.9L engine (commonly used in Dodge Ram trucks in the 1990s and early 2000s) had 2-bolt main caps, and many performance upgrades or rebuilds include the use of 2-bolt main studs for additional clamping pressure and engine longevity.

Cummins 5.9L 24V

Cummins 6.7L

Some versions utilize the newer 6.7L Cummins engines, which employ 2-bolt main caps. For most standard or moderately built engines, 2-bolt main studs are usually used for added strength. However, moving to 4-bolt main studs is typically advisable for performance builds and high modded.

When Are 2-Bolt Main Studs Used in Diesel Engines?

Rebuilds/Stock Builds: For engines such as the Powerstroke, Duramax, and Cummins diesels, 2-bolt main studs are usually applied in rebuilds or stock performance configurations where extreme RPM and torque aren’t ongoing.

Towing and Street Use: Most light to moderate tow configurations utilize 2-bolt main studs for added strength since they deliver sufficient clamping force for day-to-day driving, light-to-medium towing, and performance without the expense of having to switch to 4-bolt configurations.

Cost-Effective Strength: For price-conscious rebuilds and performance builds that do not need to exert excessive strength (such as in extreme towing, racing, or heavy-duty uses), 2-bolt main studs provide a more cost-effective and trustworthy option.

How to Install 2-Bolt Main Studs?

2-bolt main stud installation is an integral stage of engine building, guaranteeing that main caps are safely mounted on the engine block in a position to maintain the crankshaft under excessive stress. This installation accurately maintains the durability and performance of the engine, particularly in harsh situations. What is described hereinafter is the step-by-step proper installation of 2-bolt main studs.

Tools and Materials Needed

• 2-bolt main studs kit (including studs, washers, and nuts)
• Engine block (properly cleaned and prepped)
• Torque wrench
• Thread sealant (optional, depending on the application)
• Assembly lube
• Ratchet and sockets
• Main caps (with bearings installed)
• Clean rags or towels
• Engine block gasket (if necessary)

Step-by-Step Guide

1. Prepare the Engine Block

• Thoroughly clean the engine block’s main cap areas, including the threaded holes where the studs will be installed. Any debris or dirt can interfere with the installation and torquing process.
• Ensure that the threads in the block are in good condition. If the threads are damaged, it may be necessary to use a thread chaser or tap to clean or repair them before installing the studs.

2. Check the Main Caps and Bearings

• If the main bearings haven’t been installed, install them into the main caps.
• Clean the main caps and ensure they are free of dirt, oil, or debris before installation.
• Ensure that the main caps are correctly oriented with the engine block. Some blocks and caps have specific alignment, so ensure the caps are installed correctly.

3. Install the Main Studs

• Apply a small amount of assembly lube to the threads of each stud (this helps prevent galling and provides better torque retention).
• Insert each 2-bolt main stud into the main cap holes of the engine block. Make sure the studs are fully seated in the block.
• Some applications may require a small amount of thread sealant on the bottom of the stud where it enters the block. Apply the sealant only if the manufacturer specifies it, and do not use excessive amounts.
• Ensure that each stud is aligned straight with the block and not cross-threaded.

4. Install the Main Caps

• Carefully place each main cap onto its corresponding studs, ensuring it is seated correctly on the main bearings.
• Make sure to align the caps correctly with any markings or alignment dowels on the block (if applicable).

5. Install the Washers and Nuts

• Place a washer on top of each stud that will receive a nut.
• Hand-thread the nuts onto the studs. Do not fully tighten them yet—just make sure the nuts are loosely in place to hold the main caps down.

6. Torque the Main Studs

• Follow the manufacturer’s torque specifications and sequence when tightening the nuts. Torqueing should be done in stages to apply pressure and avoid gradually distorting the main caps.
• Start by tightening all the nuts’ hands until flush with the washers.
• Then, using a torque wrench, tighten the nuts in the recommended sequence, typically in a criss-cross or spiral pattern, to ensure even pressure distribution.
• Begin with a lower torque setting (usually around 30-50 lb-ft), then incrementally increase the torque in several steps, following the specified torque values.
• The final torque value is typically around 70-90 lb-ft, but it’s essential to refer to the manufacturer’s specifications for the correct values.

7. Double-Check Torque

• Once you’ve reached the specified torque values, go back over each stud and verify the torque again. This ensures that all studs are properly torqued and evenly seated.
• Make sure that the nuts turn smoothly and that no stud is binding or showing signs of uneven torque.

8. Clean Up

• After installation, remove excess oil, assembly lube, or thread sealant from the area to prevent contaminants from entering the engine.
• Recheck the main studs to ensure they are correctly installed and torqued.

Additional Tips

• Be patient and take your time to make sure everything is installed correctly. Over-tightening or incorrect installation could result in engine damage.
• Always refer to the manufacturer’s manual for torque values and installation procedures, which may vary depending on the engine type and main stud kit.
• Use the appropriate assembly lube and thread sealant (if required) to ensure proper clamping force and prevent rust or corrosion.

Final Thoughts

2-bolt main studs are a necessity for the stability and longevity of your engine, offering greater clamping force and block distortion prevention. They find the middle ground between strength and cost, making them perfect for most gas and diesel engines, including popular models like Powerstroke, Duramax, and Cummins. Not quite as robust as 4-bolt setups, 2-bolt studs are reliable enough for most rebuilds and performance builds. By installing according to the correct procedure, you can maximize your engine’s performance and longevity for years.