Thread: four bolt mains?

Tweet

I would like to know what this means. Just starting to learn engine. I am not a kid and I should know. What are the mains and do all engines have these. Thanks.

Main as in main engine journal, where the crank bearing goes and yes they all have some type of mains.

The crankshaft is fitted into the engine block on a set of main bearings. There are caps which then bolt into the bottom of the block to hold the crank and bearings in place. Most all production motors use caps which are secured with 2 bolts, although some high performance motors which would see extreme rpm's and/or extreme cylinder pressures were produced with caps which required 4 bolts per cap to secure them to the block. In extreme service, 4 bolts will keep the cap from moving around in its saddle better than 2 bolts will. If we can keep the cap from moving, we can maintain a better control of bearing clearances and therefore oiling issues.

Originally posted by thunderbird92
I would like to know what this means. Just starting to learn engine. I am not a kid and I should know. What are the mains and do all engines have these. Thanks.

main caps hold the crank in the block. four bolts is the number on each cap that holds the cap to the engine block two bolts are used in stock stuff. hp stuff use more bolts or studs to hold the cap down on the block

oh and the more holes in the block main web make the block weaker to so it some times it is toss-up