A 4-bolt main engine block provides extra strength for the crankshaft. The main bearing caps hold the crankshaft in place. In standard engines, these caps use two bolts. In high-performance or heavy-duty engines, each cap uses four bolts. The extra bolts prevent the caps from walking or flexing under high load, which protects the bearings and block from cracking at high RPM.
Mechanic Glossary
4-Bolt Main
An engine block design where the crankshaft main bearing caps are secured to the block using four bolts instead of two.
Frequently Asked Questions
It strengthens the bottom end of the engine. The extra bolts stop the crankshaft caps from flexing under heavy horsepower or load.
You must remove the oil pan and inspect the crankshaft main bearing caps. Caps with four bolts instead of two are 4-bolt mains.
Yes. A machine shop can drill and tap extra bolt holes in the block and install aftermarket 4-bolt caps.