ZMAN Z28

I rebuilt the motor (350 LT-1). I had 2 thousandth clearences, and the motor spun over very smoothe sitting on the engine stand. The machine shop checked the block, cleaned out the oil galleys, turned the crank 10 under, machined the rods with new bolts. Granted I didn't stick a new oil pump in it. More on that in a few. When my dad and me primed the oil pump, we got 25psi off the starter. I have between 700-800 miles on the rebuild. The factory oil pressure guage in the dash was 40psi when cold and 18-20 when warmed up at idle (900rpm's). When I got on it last sunday(less than 6000 rpm's), after I came to a stop, the oil pressure read about 10psi. I revved it and it went right back to 20psi. I drove it home and parked it. So thursday I put a manual guage on it. The guage has a small leak. But at idle cold, oil pressure was 40 and the factory guage read 35. After I warmed it up at idle, the factory oil pressure read 15, while the manual guage was 20. I revved it to 2000 rpm's, and the manual guage (MG) read 35psi, as the factory guage (fg) read about 18. The warmer it got, the fg read right above 10psi. Where the manual never dropped below 17-18. If I revved it to 3000-3500 rpms, the mg was at 40psi, where as the fg stayed right about 22psi. I bought a new GM oil pump and pulled the pan to replace the oil pump. I found chunks in the oil pan. So yesterday my dad and I inspected the bearings. The 1 and 2 rod bearings had some minor wiping. The #4 main rod bottom bearing was messed up, the babbit was gone in the middle, and the outside was flaking off. My crank is ruined. I'm dropping the motor out today. The machine shop said I starved it for oil. If I starved it for oil, wouldn't more then 1 bearing be messed up? I think it was a faulty bearing. As the top half of #4 only had scratch marks from the babbit going through it.

Thanks:

ZMAN Z28

ZMAN Z28

Help. ---...--- S.O.S.

SStrokerAce

Well something was up with the clearances on that bearing...

You mean .0021 for clearance? How did you measure that?

Bret

JONEZ_Z

LOL yah i think the .021 clearance would be pretty rough on bearings.

SStrokerAce

ya think? lol

ZMAN Z28

Sorry, 2 thousandth clearance. I suck with decimals. hehe. I plasti guaged it.
Acually I have 21 thousandth clearences on the rods side to side. The Chiltons (not the greatest book) says 6-14thousandths is acceptable for this.

Z

1racerdude

.021 on the side clearance is a little much for a street engine but not unheard of. The only thing that will hurt is splash on the cyl walls and oil control.
If the manual guage shows the pressure to be OK I wouldn't worry.I would mount a manual guage in the car with a LED on a HOBBS switch(adjustable pressure switch) set at 20PSI and see if it does it again.If it does THEN I would worry.
When ya let it come to idle,when the dash guage showed low,it may have been idleing slow which the sometimes do after a hard pull.

Does it have the baffle in the pan?

ZMAN Z28

Yep, I already pulled the pan, it had it in there. I inspected the mains and rods, and the crank. The crank is ruined. The #4 main bearing had all the baffle removed from the center section on the bottom half of the bearing. I pulled the motor yesterday. Baffle made it all the way up into the heads. There weren't big chunks only signs of it (tiny pieces). When I put the motor together, everything was blown out with air. I was extremely maticulious on cleanliness. There are absolutely no signs of dirt on the back sides of the bearings.

The machine shop is going to disasemble the motor. I have it tore down to a short block. The rear main seal and timing cover is still on also. I can only speculate on what they are going to find/say. But I know I put together the motor within correct tolerances except the rods side to side. But that shouldn't effect the oil starvation.

I'm not looking to profit from the machine shop. I only want for this thing to be correct. I am going to have to buy new rods and a crank. I only want machine costs. So I am trying to get my ducks in a row.

Thanks for the help so far. I'll keep any interested posted.

ZMAN

MachinistOne

Why would you re-use the old oil pump???

1&2 rod bearings are farthest from the pump, that is why they starve for oil and show more wear than the others.

ALWAYS USE A NEW OIL PUMP. That being said, use a m55a high pressure pump, and make sure your dipstick is correct. If you are swinging this thing around turns, upgrade the oil pan to a JR manufacturing which has baffles and gates plus a windage tray and scraper for cheap.

ZMAN Z28

Sometimes I do stupid things. But I still verified with a manual guage it was working. I tore the pump apart, and the gears looked good. I didn't know that the spring controlled the pressure. I have a new GM stock pump to go back in.


The #4 main is destroyed. Since #4 main is in the middle, wouldn't this get oil before the outside mains, and thus the outsides should have been starved for oil before #4?

Thanks:

ZMAN

1racerdude

Old pump is not a good idea but it obviously had some oil pressure.
Was anything hitting to get metal in the pan?Was the pickup 1/2" from the floor? Was it a stock oil pan? If so maybe the oil was climbing the back of the pan under acceleration like they all do. Did ya prime it before starting? Did ya use assembly lube? Did ya reinstall the oil cooler? Was the cooler clean?

So many things could have caused the problem.

Oil goes from the back to the front.

shoebox

That was going to be my first question. Maybe it was not the problem, but I would never, ever reuse an oil pump on an engine teardown without some real good reason.

ZMAN Z28

Ok ok, kick a man while he's down. Got some salt to rub in the wound also guys.

ZMAN

shoebox

The purpose is to also help others reading the thread.