What is a 2 and 4-Bolt Main Anyway?

Mains are what hold your crankshaft in place on the bottom of the engine. Some engines have 2 bolts or 4 bolts on each main securing the crankshaft to the engine. The good-old American theory: MORE IS BETTER!! Right?… in this case, NO.

Where the Theory Came From…

GM started making the 4-bolt main in the 1970’s because their theory was that as power increases the crankshafts would shoot out the bottom of the engine. They believed that when you increased the load on the crankshaft, you increased the load on the main caps. While this is true, as blocks evolved they became thinner and having more bolts on the bottom of the engine wasn’t the best solution.

Well, GM’s theory wasn’t as factual as we assumed because their strategy didn’t evolve with the times. Over the years, GM used the 4-bolt main as a marketing strategy to convince consumers that it was the right choice and it was for blocks made in the 1970’s. As consumers fell in love with the idea, engineers understood the concept, and GM’s car sales improved.

Everyone was happy until the 1980’s rolled around and here’s what happened…

The History

The Environmental Protection Agency, also known as the EPA drives stringent requirements that are federally mandated to regulate vehicles and make sure their safety ratings, fuel economy, smog and luxury features are up to standards. To stay in business, car manufacturers needed to build vehicles lighter and quieter with more safety features and a smoother ride. Hence why engines are now becoming smaller and lighter with the same horsepower and better fuel economy.

What does this have to do with engine blocks? Well, starting in the mid 1980’s, the EPA began a stronger enforcement with things such as Noise Vibration Harshness (NVH), which was the turning point for the aftermarket performance industry. GM, Chrysler, Ford and other car manufacturers began molding thinner cast iron engine blocks making them lighter to gain better EPA ratings for achieving more safety and better fuel economy.

What they didn’t take into consideration is that when the cast iron blocks became thinner and removed the nickel (a high strength metal material that gave the block more integrity), the blocks would flex as horsepower increased which weakened the 4-bolt main design.

In return, the 4-bolt mains continually had hairline fractures over time varying on the abuse the engine took. This caused issues that the 2-bolt mains didn’t experience since there were less bolts to cause a flaw in how the engine flexed. We discovered through our own research and development that adding aftermarket studs on a 2-bolt design is much stronger and reliable.

Now, this is not to say that the blocks that were manufactured in the late 80’s and 90’s were poor. That’s not true. They’re a better design, lighter, the rear mains are stronger and less prone to leak, the cam designs are better. Overall, it’s the block we prefer to build our engines with that has brought us the most success and almost a zero-failure rate.

Here’s the facts:

• The block you want is from 1987-2002. This is also known as a 1-piece rear main block or a full round seal block. Stay away from the 2-piece rear main!
• A 2-bolt main with aftermarket studs is stronger than a 4-bolt main block, less prone to crack, and can take up to 600 HP on a seasoned block.
• NEVER buy a new block that does not have the manufacture name on it such as “Dart” or “GM Performance” because it’s made overseas and it is CHEAP. These blocks are brittle and will crack.
• Do not fall into the “4-bolt main” marketing trap. Most of the engine builders online, including some big brands, will drill extra holes on their 2-bolt main blocks and it makes the mains weaker and more prone to cracking.

New or Seasoned Block

As you digest all the information we’ve provided, we’d like for you to keep in mind that all these facts apply to seasoned blocks ONLY, also known as remanufactured blocks. When you start to dive into NEW blocks that manufacturers are offering you really must be careful.

Most new engine blocks are cheaply made in Mexico or overseas, have weak mains, poor machining, and are built by underpaid employees who don’t really care. These blocks are more prone to crack due to lack of quality control.

In ANY industry, the people creating the product is senior to the process. If you don’t have quality people, it’s hard to have a quality product. It’s proven that when you have the right people who care about what they do, you will have a solid product because it matters to them. What a concept, right?

Therefore, when you hear people say, “just buy a crate motor from GM” it gets consumers into a lot of trouble. GM has multiple facilities all around the world and their Chevy small block engines get the worst reputation (also known as target engines or target master engines) because it has the lowest quality control in their entire operation and is based out of Mexico. We’ve seen hundreds of GM crate engine customers come to us out of devastation when their block fails, and they have a warranty with so much fine-print stating it doesn’t cover it.

Cheaper Isn’t Better

We hope you’ve learned some valuable tips that we love sharing with our consumers! Buying an engine isn’t a cheap purchase, but sometimes people turn to cheap and consider it convenience. You’re wasting your money and we don’t want that! Always do your homework and you can always count on West Coast Engines to provide you with quality engines, but also the quality content you’re looking for when doing your research.

Other Related Posts:
Read our expert guide on what a crate engine is here.
Expert Tips: Buy A Crate Engine Or Build One?
What You Need To Now Before Buying A Cheap Engine