I tore down my 1970 model 383 to replace the rear main seal. I pulled the caps to lift the crank and noticed some serious wear on the main bearings. The cap nearest to rear of the engine actually was destroyed. What caused this, and what should i do when replacing them to make sure it doesnt happen again?

I'd appreciate the help.
Pics are in order from the rear of the engine to the front.

2nd from rear

3rd from rear

4th from rear

front main cap

At this time i don't have any pictures of the bottom caps until i go rent a harmonic balancer puller.

EDIT! Don't have any picture of the TOP bearings. Got confused with the engine upside down!

You mean upper bearings because those are the lowers. How many miles on this engine? Looks like some trash got into the rear bearing and I would mic the crank and cheak for damage to it.

Guy i bought it from many years ago said it only had about 1100 miles when i bought it. I would guess anywhere from 2000-3000 miles, as i didn't drive it much.

As micing it, you mean just check the runout?

Could this be cause by the transmission bolts being loose/missing? I found a bolt missing from the bellhousing mount, and a few others seemed pretty loose.

Yes check for roundness. A loose trans could cause excessive wear but to do that much it would have to be darn near falling out loose. That is a lot of damage for that few miles.

Right, he could of been blowing it out his @** but the rest of the engine looks pretty clean without much wear. Is there a chance that since the rear main seal was leaking so bad that i just ran it short of oil?
they all look unevenly worn, only the rear one took it hard though.
Also as i dissassmbled all the broken pieces were sitting right where they came off of. I don't think any parts of the bearing were scattered through the engine.

Acid in the oil can cause the damages you see like on the rear main bearing, so can dirt #1 main bearing gets oiled first, #5 gets oiled last Have you looked at any of the rod bearings yet? If not look at them also, the main bearings get oil first and many times they will eat the dirt, if it is bad enough the metal and dirt from the mains will be washed into the rods also Let us know what you find BTW, how long has it been since the motor was built and ran for the first time years or months, not miles

I bought the car 7 years ago. Drove it right away for about a year and a half. Sat for a year, then drove it for another year and a half. The last stint as been sitting for about 3 years. I havn't tried to start at all in the past 3 years becuase the water pump went out and the fan went through the radiator. I finally decided to just go back through the car so i pulled the engine. I'm gonna pull the crank and take it to have a machine shop check it out. I tried mic'ing it but my tools are crappy, and combined with the wobble of the engine stand, i couldn't get an accurate reading.

If its no good, i might just have to look into stroking it.

Oh ya is the number 1 bearing the front of the engine or back?

You can look on back side of bearing for bearing mfg date and possibly the decimal of ground crank size too for a basic date of engine assembly. usually vague as new bearings are sometimes a couple of years old when purchased.

upper bearing says
6 99 June 1999?
NB 2065P
010
upper

Lower says
A Clevite
77


So i guess they've already been ground -.010?
How low can you go if they need another grind. I don't see any large gouges.

Also i noticed a slight ridge in the center of the journals where the oil passway is on the bearings?

Could this indicate too tight of bearings, or is this common?

A ridge is not common but could have been made by the oil hole , clearances its 2 tight or the crank journals are not round . The rods I bet will look as bad or worse , the stuff that came off the bearings went thru the oil hole to the rod bearings .

You are looking at a rebuild if the crank turns out to be wrong I wouldn't trust the rest of it .

curious if they guy said it was low miles, what do the bores look like?

i have taken apart 150K motors with bearings that looked better.

bores look good, but no crosshatching. If those bearings are dated 99 then that probably lines with his story. If i got the crank straigtened away, and put new main and rod bearings it. Shouldn't it be good to go?

My only fear is that maybee it got some shoddy workmanship. Either that or i destroyed the bearings some how.

I would check the crank for straightness and you may well need to check the block's line bore. I'm thinking there damage seen may not be due to trash in the oil, but instead by a bent crank and/or line bore that is not true.

Astrobuf

Lots of engines are rebuilt on a 'budget' if it was holding good oil pressure only the rod bearings and rings are replaced. Maybe even the valves reseated.