I just installed a 385 into my 96 z28 and the center 3 main bearings are shot and the thrust is wore on 1 side after 15min break in and about 60 miles. The shortblock was built by performance engineering and i out the heads anf intake on. I ran the it at 1500-2k for the first 15min and then went over everything and changed the oil. I drove it the a couple times the next couple of days and it started to lose oil pressure. I rolled into a little in 3rd gear after about 50miles from 3-6k and thats the only time it was over 3500. The guy that built the motor seems to be unsure and he has been doing it for 25years he thought maybe detonation or crank flex. The first filter did show a few signs of shavings after i cut it open the other day. Anybody have any idea on what could cause just the center 3 mains to wear out? Any help is appreciated. (i did prime the oil pump b4 startup and the beaings show no signs of dirt or debris)

Motor specs

Eagle cast crank 3.75"
eagle h-beams 6"
srp -4cc pistons
LE3 heads and cam
ported intake
double roller chain
e- water pump
hv pump
canton pan

Block work

Fully balanced
align bored
arp hardware
.040 over w/ torque plate
clevite 77 H-sereies bearings
zero decked block

i think thats it sorry for the long post

Scott

 

Sounds like the block needed line boring and didn't get it.

 

they said it wasnt too bad bt i had them do it anyway and i asked it that could bethe problem and he assured me that it wasnt. THat was my initial thought as well

Thansk Scott

 

Well if it was line bored that's not the problem, the problem is they didnt' balance the rotating assembly and it was probably vibrating and wore the bearings completely down.

 

which side of the thrust bearing was wore. toward the front or back?

 

Ya hardly EVER have a center main problem with a SBC.
The wrong size bearings may have been installed. The thrust bearing issue would be due to a lack of oil or there was not enough clearance(end play).
Crank flexing is a non issue no longer than it was run.
Did ya put the same flywheel and balancer it was balanced with on the engine?

 

Noticed your other thread about a leaky oil pan...how much oil leaked out?

 

i used the same flywheel and balancer, i am not sure which side was wore it had .005 clearance on the build sheet.

Scott

 

it only leaked maybe a 1/4 quart out of the 8.5 that i had in it. It was never ran low and had good oil press initially 40+ at idle when hot. before i took it back out it only had 15 and would only make 35 if you revved it

Scott

 

That is a little tight but should have been OK.

 

Was the engine neutral balanced?

 

Hey,
I've had an eagle crank before with machine marks (rough) left in the thrust area of the crank. You can't really feel them with your fingers (you can grab them with your fingernails) but if you look at them with your eye you can see them. I had to get the crank polished back there before I put it back together. Sounds like something similar on yours. Might be worth checking.

 

maybe too high of oil presure? could have caused blow by and thus not enough lube for the bearings.

 

Something wrong with the clutch setup and it pre-loaded the crank forward?

Have had several customers over the years not get their torque converters fully seated, and they wiped the thrust in no time....

 

It would be nice to have some pics....something that didn't get cleaned out broke loose and plugged the oil galley?