VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Inserts in the mains from when?

Refering to the parts books, inserts are listed from 1929 on up for the main bearings. In a discussion on another forum it was suggested that they were only shells that had to have the babbit poured into them and then line bored. That doesn't seem logical to me. I mean, the object of main shells is that they already have the babbit poured and machined to size. Are there any 30's era Chevy engine builders out there that have been through this?
Denny Graham
Sandwich, IL

I am probably not the best one out here but they are shells. You buy them and have them line bored to the size of your crank. I had my 31 crank ground on all the mains and then had my new mains line bored to match the crank. If they were already finished then you would have to grind your crank to match the new mains. Hope this helps a little. Good luck with your project.

All 6 Cyl. Chevrolet engines had main bearing inserts. The 1929-1947 engines required the main bearing inserts to be line bored when the inserts were replaced. This prevented the replacement of just one insert.
The 1948 engine introduced precision type inserts. The inserts then did not require line boring and just one could be replaced if necessary.
After 1948 Chevrolet sold precision type inserts for 1929-1947 engines. For initial installation it was necessary to replace all the inserts but in the future just one could be replaced. This also required under sized bearings if the shaft was turned. With the line bore type the babbit was just bored out to the required undersize.
The 1932-1936 Ford V8 engines had the babbit poured directly into the block and cap and then it was line bored so nothing could be replaced. An old Chevrolet could have the mains adjusted many times, the Ford required a rebuilt engine when they got miles rolled up. The cylinder walls were usually worn out by that time also.

Through the years they made the babbit thinner for the rod and main bearings. The thinner babbit compressed less and fewer adjustment were required. The precision bearings were of the thin babbit type and are very desireable.

OK guys, thanks that should settle it. That's a new one on me.
Denny G