Hey guys....i just finished rebuilding my brothers engine...the original problem was a spun connecting rod bearing... so we desided to rebuild the whole thing....But being that my brother is only 18 we wanted to do an inexpensive rebuild.

When we took the engine apart we took the parts to the machine shop...The crank was trash and the block needed to be bored...so we went to the junk yard and bought a block and a crank...the machine shop said both were good and had all this done at the machine shop:

Cleaned all parts (block, rotating assy, heads)
-Honed the cyl. walls
-Cleaned up the journals on the new crank (they said that everything was within spec..no machine work needed)
-New valve stem guides, seals, springs and vavle job
-And i think the machine shop said that they installed a sleeve in the connecting rod that spun the bearing.
-Installed new Freeze plugs and cam bearings

Because they said that everything was withing stock spec we orded a rebuild kit. Got new:
-Main bearings, connecting rod bearings, piston rings, full gasket set, umm...think that was it.

Here is ONE problem though...when i took apart the oil pump to check its condition i found that the relief valve was stuck closed...i managed to clean it up and lubed it all up..now it is functional...BUT the gasket set did NOT come with the oil pump gasket...so i used the old one... ...it still looked in great shape...and everything else was functional.

NOW...the engine starts up fine and runds fine...but the oil pressure is a little iffy...when at idle it is at ~20psi (cold) and stays that way when you rev it...but when it warms up...you dont have any oil pressure at idle but if you rev it a little (1,500 rpm) you get about ~15psi.

Any thoughts? I really dont want to replace the oil pump cause we just put the engine in...

OHH yeah...i also bought Mobil 1 Synthetic 10W-30 engine oil...i noticed on the oil fill cap that the engine needed 5W-30...i really dont think this would make a diff....and i didnt buy a new cam. just new bearings.

I really apreciate any help here...sorry for the length...but i wanted to make sure i gave all of the info. Thanks.

-Mike

 

I really dont think it makes a diff but my brothers car is an 87 firebird with the 2.8L V6 in it.

-Mike

 

Did the machinist say they "resized" the rod?

#1 part to make sure you replace with new when rebuilding an engine, no matter what else you do, is the oil pump.

"Oil pump gasket"? The only 2.8 I've had apart was an '80 in a Citation, but it didn't have a gasket for the oil pump. The pump failed the day after it turned over 150k miles, by the way.

Go get a new oil pump and put it in. Before you drive it and spin another bearing.

10W30 or 5W30 won't make any difference with regard to your issues. Synthetic is a good idea after the engine is broken in, though.

 

yeah....i guess i should have replaced it...hindsight is 20/20 ya know. but when i took it apart it looked really clean...so figured...hey why not save $75 dollars...ohh well

thanks for the input

-Mike

 

Did you actually check the bearing clearance? You always should, I never trust machine shops, I've seen them make too many mistakes. The machine shop might have said everything was within spec. but if the crank journals where on the small side of the tolerance (likely) and you put standard bearings in it with a wore out oil pump odds are your going to have low oil pressure.

 

i was thinking the same thing....and to be honest...no i didnt check the clearance with plasti-gauge (or how ever it is spelled) it is one of those things..."i should have" but hell it was my first engine and i was so excited to get the thing running....ohh well...when i chenge the oil pump i will check the clearances.

-Mike

 

Are you checking the oil pressure with a separate mechanical gauge or the dash-mounted factory unit? I'd verify the dash gauge with a mechanical test gauge before I got too excited about removing the oil pan again...

 

Yeah...i just did that today....just to make sure....still no oil pressure....after i finish typing this...i am going to remove the engine again....ohh well...look what you get for not doing it right the first time...live and learn i guess....thanks for everyones input...ill let yall know how everything goes.

-Mike

 

Take a good close look at the rear main bearing shells, and inspect the rear cam bearing position and placement. All lubrication must go through those passages unless you've converted to priority main oiling. Another thing to watch for is the sealing at the distributor lower end. If your distributor is sloppy in the block, you'll lose pressure there. too.

 

the oil pressure on my 305 has been acting up lately. starts about about 45 when cold and ends up around 30 while driving and 15 at idle...i know 15 at idle is fine but is 30psi enough about 4500rpm?

 

The old rule of thumb for small block chevys is to have at least 10 PSI for every 1000 RPM:
10 psi@1000 rpm
30 psi@3000 rpm
50 psi@5000 rpm

But I've seen them live a long time on a lot less.

 

well i just need the 305 to last till the end of summer when i can afford the goodwrench lo5 and a intake, distributer and everything then its going out.