4 bolt main or 2 bolt?????

[chevy girl]

What is the difference between a 4 and 2 bolt main?? I'm thinking about selling my old engine, and have a friend wondering what it is. I have NO idea... (am I showing my inexperience here?) :7 Just wondering if yall could help me out?

 

[mikesters1950]

Chevy girl,
2, or 4 bolt main, refers to the number of bolts holding the crankshaft main bearing caps in place. The 4 bolt main engines are generally considered more desireable, and stronger. Unless you are building a pumped up motor, 2 bolt mains have been used very reliably for many many years. If the oil pan is removed, you can see the bearing caps, otherwise an engine number, or possibly a make and model the engine came out of can be used to determine which motor it is. Just for info, another item people look for when buying/building an engine, is the type of crankshaft, and or connecting rods it has. They will either be cast (weaker), or forged (stronger). Again, mostly important if you are building an engine with big horsepower gains over the stock engine. Hope this helps some. Post more info on the engine if you need help figuring it out, and someone will be able to help.......Mike

 

[dvalentine]

Hi C.G. !

Write down the block casting numbers that are stamped into a the block on the flange edge of the rear of the block, near the bellhousing mating surface. They are found below the left cylinder head.

THEN, take those numbers and go to http://www.mortec.com/castnum.htm

The numbers don't lie and will tell you exactly what it is you have there.

DValentine

 

[74sbc]

on the crankshaft, there are plates that hold the crank in place, they are called mains, a two bolt main means that their is two bolts (one on each side) holding it in place. Four bolt means two on each side.
4 bolt is better because it is stronger and can handle more torque higher rpms.