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Home » How to Easily Identify a 4 Bolt Main 350 Engine: A Comprehensive Guide

How to Easily Identify a 4 Bolt Main 350 Engine: A Comprehensive Guide

How to Identify a 4 Bolt Main 350

A 4 bolt main 350 can be identified by the presence of four bolts attaching the main bearing caps to the engine block. This configuration provides additional strength and stability to the engine.

In general, 4 bolt main engines are considered more desirable for high-performance applications due to their improved durability and ability to withstand higher levels of stress and power. These engines are commonly used in chevrolet small-block v8 engines, especially those produced during the 1960s and 1970s.

The identification of a 4 bolt main 350 can be important for collectors, restoration enthusiasts, and individuals seeking a reliable and powerful engine for their vehicles.

How to Easily Identify a 4 Bolt Main 350 Engine: A Comprehensive Guide


Understanding The 4 Bolt Main Engine

The 4 bolt main engine is a common term amongst automotive enthusiasts and refers to the number of bolts used to secure the engine’s main bearings. These main bearings are essential for proper engine functioning as they support the crankshaft, which in turn powers the vehicle.

In this section, we will dive deeper into what exactly a 4 bolt main engine is, its significance, and the benefits it offers.

What Is A 4 Bolt Main Engine?

A 4 bolt main engine is an engine design where the crankshaft is secured to the engine block using four main bearing caps. These caps are fastened with four bolts, evenly distributed around each main bearing, providing additional stability and strength to the engine.

This design serves to enhance the engine’s structural integrity and withstand higher levels of stress and torque.

The Significance Of The 4 Bolt Main Design

The 4 bolt main design is crucial because it plays an instrumental role in maintaining the engine’s stability and prevents any potential crankshaft movement. Some key points to note about the significance of the 4 bolt main design are:

  • Enhanced strength: The additional bolts on the main bearing caps distribute the forces more evenly, reducing the likelihood of bearing cap movement, main bearing wear, and potential engine damage. This results in a more reliable and durable engine overall.
  • Reduced engine flex: The 4 bolt main design helps minimize engine flex, which can occur under high-performance conditions. Reduced flex ensures the engine maintains optimal alignment, increasing both power and efficiency.
  • Improved durability: By providing better support and stability to the crankshaft, the 4 bolt main design helps mitigate potential issues such as main bearing wear, crankshaft movement, and ultimately prolongs the engine’s lifespan.
  • Compatibility with high-performance applications: The increased rigidity offered by the 4 bolt main design makes it an excellent choice for applications with higher horsepower and torque levels, such as racing or high-performance engines.

Benefits Of A 4 Bolt Main Engine

The 4 bolt main engine design comes with several notable benefits that make it a preferred choice for enthusiasts seeking reliability and performance. Here are some advantages of a 4 bolt main engine:

  • Increased strength and durability: The additional bolts and enhanced stability of the main bearings provide the engine with improved strength and durability, ensuring it can handle higher stress levels and longer periods of operation.
  • Enhanced performance: The reduced engine flex and improved alignment from the 4 bolt main design contribute to better power delivery and overall performance. This is particularly beneficial in high-performance applications where power output and responsiveness are crucial.
  • Reduced risk of engine failure: The 4 bolt main engine design significantly lowers the risk of main bearing failure, which can result in catastrophic engine damage. The added stability and support provided by the extra bolts minimize the chance of bearing cap movement and subsequent engine failure.
  • Longevity: The enhanced durability and reliability of the 4 bolt main engine design contribute to a longer engine lifespan, making it a suitable choice for those seeking an engine with increased longevity.

The 4 bolt main engine design offers improved strength, stability, durability, and performance. Whether you’re an automotive enthusiast or considering a high-performance application, understanding the significance and benefits of the 4 bolt main engine design can help you make informed decisions when it comes to engine selection.

Visual Characteristics Of A 4 Bolt Main 350 Engine

If you’re in the market for a 350 engine, you may come across the terms “2 bolt main” and “4 bolt main. ” These terms refer to the number of bolts that secure the main bearing caps within the engine block.

While a 2 bolt main engine is common for most applications, a 4 bolt main engine offers improved strength and durability. In this section, we will explore the visual characteristics that can help you identify a 4 bolt main 350 engine.

Exterior Features To Look For:

  • Look for a wider, more pronounced rear main cap that accommodates four bolts instead of two. The increased number of bolts adds stability to the engine block, making it more resistant to flex during high-performance applications.
  • Check for additional machining on the block around the main bearing caps. A 4 bolt main 350 engine will typically have extra material removed to allow for the larger main caps.
  • Inspect the block for reinforcement webs between the main bearing journals. These reinforced areas provide additional support, ensuring the main caps remain securely in place even under extreme conditions.

Engine Block Markings:

  • Search for any marks or stampings on the engine block that indicate it is a 4 bolt main. Look for numbers such as “010,” “020,” or “604” that relate to the specific main bearing cap configuration.
  • Keep an eye out for any manufacturer-specific codes or symbols that indicate a 4 bolt main engine. These marking systems can vary depending on the engine manufacturer, so reference an engine identification guide for precise information.

Identification Numbers:

  • Locate the engine identification numbers stamped on the block. These alphanumeric codes often contain clues about the engine’s characteristics. Refer to a reliable engine decoding resource to decipher the numbers and determine if it is a 4 bolt main 350 engine.

Casting Numbers:

  • Check the casting numbers on the engine block, usually located near the bellhousing area. These numbers provide details about the casting process and can help verify if the engine is a 4 bolt main variant. Cross-reference the casting numbers with a comprehensive database or consult an expert to confirm the engine’s configuration.

Differentiating Between A 2 Bolt And 4 Bolt Main Engine:

  • Look for the total number of bolts securing the main bearing caps. A 2 bolt main engine will have two bolts, while a 4 bolt main engine will have four bolts.
  • Identify any extra reinforcement or machining on the engine block that accommodates the additional bolts. This visual distinction can help you differentiate between the two types of engines.

Bolts On The Main Cap:

  • Count the number of bolts present on each main cap. A 4 bolt main engine will have four bolts on each cap, whereas a 2 bolt main engine will only have two.
  • Note that the bolts on the main caps of a 4 bolt engine are evenly spaced, providing a more balanced distribution of load compared to the wider spacing found in a 2 bolt main.

Bolts On The Center Caps:

  • Look for bolts on the center caps of the engine block. In a 4 bolt main 350 engine, the center caps will also feature four bolts, indicating its enhanced strength and stability.
  • Conversely, a 2 bolt main engine will have two bolts on the center caps, creating a noticeable visual distinction.

By familiarizing yourself with the visual characteristics of a 4 bolt main 350 engine, you can accurately identify this high-performance variant. Remember to inspect the exterior features, check for specific markings and numbers, and differentiate between the number of bolts on the main and center caps.

So, when it comes to finding the perfect engine for your needs, you now have the knowledge to make an informed decision.

Performing A Visual Inspection

Before purchasing a 4 bolt main 350 engine, it’s important to perform a thorough visual inspection to ensure its condition and authenticity. This inspection involves examining the engine block, locating the vin code, checking for reinforcement webs, identifying the main caps, counting the bolts, and investigating any previous modifications.

Here are the key points to consider when performing a visual inspection:

Examining The Engine Block

  • Inspect the engine block for any cracks, warping, or damage.
  • Look for any signs of repairs or welding, as these could indicate previous issues.
  • Check for the presence of any identifying marks or logos on the block.
  • Ensure the block is clean and free of excessive rust or corrosion.

Locating The Vin Code

  • Locate the vin code on the engine block. It is usually located on a flat surface near the front of the block.
  • Verify the vin code with the vehicle’s registration or documentation to ensure it matches.
  • Note that the vin codes for different vehicle models and years may vary in terms of location and format.

Checking For Reinforcement Webs

  • Look for reinforcement webs in the main bearing saddles of the engine block.
  • These webs, typically in the shape of “x” or “y,” add strength to the block.
  • Ensure that the reinforcement webs are intact and not cracked or damaged.

Identifying The Main Caps

  • Locate the main caps on the engine block. These are usually positioned on the bottom side of the block.
  • Check for any visible markings or identification numbers on the main caps.
  • Verify that the main caps match the engine’s make and model.

Counting The Bolts

  • Count the number of bolts holding the main caps in place.
  • A genuine 4 bolt main 350 engine will have four bolts per main cap.
  • Ensure that all the bolts are present and tightened properly.

Tips For Inspecting Used Engines

  • Look for signs of wear and tear, such as excessive oil leaks, rust, or corrosion.
  • Check the overall cleanliness of the engine, as a well-maintained engine is often an indicator of its overall condition.
  • Consider conducting a compression test to assess the engine’s internal condition, particularly the piston rings and valve seals.
  • It may be beneficial to seek the assistance of a qualified mechanic for a more comprehensive inspection.

Signs Of Wear And Tear

  • Inspect the engine for any excessive wear on the cylinder walls, pistons, and bearings.
  • Look for signs of oil sludge, as this could indicate poor maintenance or internal issues.
  • Check the condition of the timing chain and gears, as they are crucial components for engine operation.

Investigating Previous Modifications

  • Determine if any modifications have been made to the engine, such as aftermarket parts or performance enhancements.
  • Consider the impact these modifications may have on the engine’s reliability and overall performance.
  • Look for signs of amateur modifications or improper installations that could lead to potential issues.

Questions For The Seller

  • Ask the seller about the engine’s history, including previous maintenance, repairs, or rebuilds.
  • Inquire about the reason for selling the engine and if they can provide any documentation or proof of its authenticity.
  • Request any additional information, such as the engine’s mileage or usage history.

Performing a visual inspection is a crucial step when identifying a 4 bolt main 350 engine. This process allows you to assess the engine’s condition, verify its authenticity, and make an informed purchasing decision.

Additional Ways To Identify A 4 Bolt Main 350 Engine

If you’re on the hunt for a 4 bolt main 350 engine, there are several additional ways you can identify this powerhouse. From researching engine codes to seeking advice from experts, let’s explore some practical methods to help you find what you’re looking for:

Researching Engine Codes And Suffixes

  • Engine codes and suffixes can provide valuable information about the type of engine and its characteristics.
  • Look for numbers and letters stamped on the engine block or cylinder head to determine the engine’s origins.
  • Decode the engine code and suffix using online resources or engine identification books and manuals for a comprehensive understanding.

Understanding Engine Code Abbreviations

  • Engine codes often consist of a series of letters and numbers that can seem confusing at first.
  • Gain familiarity with commonly used abbreviations to decipher engine codes with ease.
  • By understanding these abbreviations, you’ll be able to identify key features, such as the type of engine, its displacement, or if it’s a 4-bolt main.

Finding Information Online

  • The internet can be a treasure trove of information when it comes to identifying engines.
  • Utilize online databases, forums, and websites dedicated to engine enthusiasts to gather information about the 4 bolt main 350 engine.
  • Research articles or blog posts that specifically discuss engine identification methods to gain insight into your search.

Consult With Experts Or Mechanics

  • Seek guidance from experienced professionals who can provide expert advice on engine identification.
  • Consult with mechanics or experts who specialize in engine rebuilding or restoration for their insights.
  • Their knowledge and expertise can be invaluable in accurately identifying a 4 bolt main 350 engine.

Seeking Professional Advice

  • Reach out to automotive professionals, such as engine builders or restoration specialists, who have hands-on experience with 4 bolt main 350 engines.
  • They can offer guidance based on their expertise and help you navigate the process of identifying this specific engine type.

Connecting With Engine Enthusiasts Or Forums

  • Engage with engine enthusiasts and join online forums or communities dedicated to engine identification.
  • Building connections with like-minded individuals can provide you with a wealth of knowledge and resources for identifying a 4 bolt main 350 engine.
  • Engage in discussions, ask questions, and share your findings to collaborate with others on your quest.

Utilizing Engine Identification Resources

  • Take advantage of various engine identification resources available, both online and offline.
  • Engine identification books and manuals contain comprehensive information that can guide you towards identifying a 4 bolt main 350 engine.
  • Online databases and forums specifically focused on engine identification can provide detailed insights and help you determine if the engine you have is indeed a 4 bolt main 350.

Remember, identifying a 4 bolt main 350 engine involves thorough research, understanding engine codes and abbreviations, and seeking guidance from experts. Utilize all available resources and enlist the help of engine enthusiasts to ensure accurate identification. With dedication and the right information, you’ll be one step closer to finding your desired 4 bolt main 350 engine.

Frequently Asked Questions On How To Identify A 4 Bolt Main 350

What Is A 4 Bolt Main And Why Is It Important?

A 4 bolt main refers to an engine block with four bolted fasteners securing the bearing caps. It offers better engine strength and durability.

How Can I Identify A 4 Bolt Main 350 Engine?

To identify a 4 bolt main 350 engine, check for four bolts securing the bearing caps at the bottom of the engine block.

What Are The Advantages Of A 4 Bolt Main 350?

A 4 bolt main 350 engine provides enhanced stability, reduced engine flex, increased strength, and improved performance.

Is A 4 Bolt Main 350 Engine Better Than A 2 Bolt Main?

Yes, a 4 bolt main 350 engine offers better strength, durability, and reliability compared to a 2 bolt main.

Can I Convert A 2 Bolt Main To A 4 Bolt Main?

Technically, it is possible to convert a 2 bolt main to a 4 bolt main, but it requires modifying the engine block and may not be cost-effective.


Identifying a 4 bolt main 350 engine can be crucial for enthusiasts and mechanics alike. By understanding the key features and visual cues, you can confidently differentiate between a 4 bolt main and other engine types. Begin by inspecting the engine block for the number of bolts connecting the main caps, as a 4 bolt main will have four bolts in each main cap.

Furthermore, look for a casting number on the block as this can help determine the type of engine. Additionally, check for a specific casting mark, such as “010” or “020,” which is often associated with a 4 bolt main 350 engine.

Finally, review the engine’s history and documentation, paying close attention to any information that confirms it as a 4 bolt main. By following these tips, you can confidently identify a 4 bolt main 350 engine and make informed decisions when it comes to your automotive needs.

Happy engine hunting!

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