Gun Laker

Here is my dilemma. I just finished rebuilding a SBC 350 from a 1977 Vette. The original engine was pretty clean and did not need to be machined as well as the crankshaft did not need any machining. So I used standard bearings, pistons and rings. Used plastiguage on the bearings and all were within specs. I put in a mild cam with new bearings as well. The holes on all the bearings were aligned and everything was torqued and re-torqued. Now I am getting OK oil pressure at the start when the oil is at room temp, some oil comes through the rods with oil priming with the correct priming tool and a good drill, and now as the engine runs, but not much oil. Pressure at start up is over forty on the in car gauge and close to forty on a mechanical gauge on the block by the distributor. As the engine warms, the pressure will state near forty at 2000 rpm's in the car, but drops on the mechanical gauge. At idle the pressure is low around 10. The lifters get noisy as the temp warms as well. The valves were set at zero lash one cylinder at a time, then tuned by listening as the engine ran. The oil pump is new as well. I am thinking three things. One, the bearings have too much clearance, two, the oil pump is bad some how or has issues with the pick up, or 3, one of the welch plugs in the front is leaking. Some how my pressure is not what it should be and the top is not getting enough oil. I am looking to see what other opinions you folks may have, and what step would you take next if you were me.

1980 blue L48

Main bearing clearance should be .0008-.002, with about .001 preferred.
Plastigage would not reveil any out of roundness that you have. Oil pressure is a result of A resistance to Flow. If it flows easy as in large
Clearances lower pressures will be seen. Did you mike anything? Rod bearing clearances have a lesser affect than Mains do. Just my thoughts

mr.beachcomber

Did you have the block hot tanked before re-assembly? Normally, a shop will knock out the oil passage plug (see John Lingenfelter on Modifying Small Block Chevy Engines p. 145) to boil out the internal oil passages. It's actually a galley plug that forces oil from the pump to the oil filter pad. If the plug is missing, the oil has a direct shot to the top of the block and the takeoff for the oil pressure sender. Overall oil pressure will drop drastically (usually 25 psi or more) once the engine and oil have warmed up.

Hope this helps!

Gun Laker

Can that plug be checked without tearing the engine apart too much? I don't have a vivid memory of that.

mr.beachcomber

You would need to drop the oil pan and remove the oil pump along with the rear main bearing cap to check for and/or replace the plug.

To just check for the plug, you might be able to to remove your oil pressure sender fitting, stick a coat hanger down the passage to see if you meet resistance before reaching the rear main bearing cap. (If the length of the wire is roughly equal to the distance between the top of the top of the block and a point just above the oil filter pad, the plug should be there.

I've attached a picture with the plug location circled.

Peterbuilt

Not sure if this is causing your problem but if your going to check the plug here are the instructions from How to Build a Small Block from S-A Books.

Iroc57

You asked what the next step would be if I were you...

Thicker oil and see where you are at, it may fix your issue for now. If you have 10lbs at idle and it goes up with rpms heavier oil will "fix" it. It is an old school bandaid but you never know...it could be a 50K mile bandaid

Just my $.02

Ganey

mr.beachcomber may be right.

AS for the oil. What was oil pressure before rebuild? What was oil weight before & now? Did you use a high volume pump?
I assume you positioned the pickup carefully.

mysixtynine

Are lifter galley plugs behind the camshaft gear installed?

Seen the machine shop take them out when hot tanking and then no one puts them back in.

Gun Laker

The oil pressure before the rebuild was better when it was warm than it is now. Also I did not have any lifter noise. I did set the pickup about 1/2 an inch from the bottom of the pan, but I have given the pickup issue some thought and I have not ruled it out. The Melling pump I put in was to be a high volume pump. The gallery plugs in the back are in and I have not noticed not even one drop of oil leaking anywhere outside the block. Now I know that if I pull the pan and replace the pump that would rule that out, and if I pulled the front cover I could see if any plugs came out. A couple of you have suggested the plug in the filter area, and I can say that a man that was assisting put that plug in, so I have to take his word for that, but I will double check as I don't remember if it was a press in or screw in plug. The oil I have in it now is 5w-30, so it is kinda thin, but my gut tells me its more than a viscosity issue. But before I start tearing everything apart, I am looking for as many opinions that I can get. Thanks for all the great feedback and I would love some more.

Gun Laker

PS thanks for the great diagrams and pics!

63mako

Don't tear anything apart yet. The oil you are running is 5W when warmed up. 5W-30 is not thick enough for the 77 engine with stock clearances when the car was new let alone one slightly worn at the main and rod journals with stock size bearings. You have good cold pressure when the oil is 30 weight. This tells me all is probably fine internally. Put some 15W-40 in it with good zink levels and run it till warm and see where your at. If you went back with a flat tappet protect it with the right oil with high ZDDP levels or you will be building it again.

mr.beachcomber

I believe that your pump pickup is too far away from the bottom of the pan. In practice, the pickup should be no closer than 1/4" and no further than 3/8" from the bottom of the pan. If nothing else, change the pickup height to get it closer to the pan.

BTW, a high volume pump can drop the oil level very quickly due to the volume of oil it sends upstairs to the heads and lifter valley where the oil drains back very slowly unless the drain back holes have been opened up and/or the casting flash removed. I have always used HV pumps with increased system oil capacity either due to a larger pan or oil cooler installed in the oiling system.

Good Luck!

mr.beachcomber

Not to pick on Iroc57 since the following is just my own humble opinion.

If the oil galley plug to the oil filter is missing, your oil is taking the path of least resistance to the top of the block bypassing the oil filter for the most part. Your engine is rebuilt and as it breaks in there will be plenty of metal debris circulating in your oiling system that won't be trapped by the oil filter. You've already taken the time and money to rebuild the engine, don't take a chance on throwing it away by blowing the engine due to damage to the main/rod bearings or tearing up your cam & lifters.

Additionally, if the plug is missing, all the upper engine oil is draining back down into the sump once you cut the engine off giving a false impression of the true oil level on the dipstick. (This is oil that dumps out of the oil filter mounting flange when you take the oil filter off during an oil change.) Don't let the oil get anywhere near the "add" mark on the dipstick until you fix the problem.

Ganey

You need thicker oil as 63mako said.
If you have stock oiling system & pan, I would remove the high volume pump.

Iroc57

No offense taken here... I will never be accused of doing thing the "right" way

5W-30 is too light for that engine IMHO though

Gun Laker

I pulled the oil pan and the the pick up seemed a bit high. Some people thought that a high volume oil pump with a standard pan might be cause me some pick up issues. So I will put a standard volume and use some heavier oil before taking the next step. I will also spot weld the pick up and prevent any movement that may have occurred. I had 5w-30 oil in the engine so I will go up a few and retry. Thanks for the continued feedback!

Duane4238

Something else no one seemed to pick up on was the fact that you said you set the valve lash at zero. I'm assuming you have a hydraulic bump stick. I've always adjusted lash to zero and then 1/4 turn past that on all my engines. This could be where your lifter noise is coming from with the 5w-30 oil as it gets hotter and thinner. I'd be running 15w-40 synthetic in a brand of your choice. Also, lose that high volume pump for a standard pump. Good luck. We all know that terribly sick feeling you get when you rebuild something and then have problems. Don't worry, you'll solve it.

Gun Laker

Good tips. Thank you, you're right I will solve it and sometimes that how we learn and learn more than we thought we would!

BLOCKMAN

Leaving the plug out of that passage and affecting oil pressure has been proven to be a myth as I don't know hy John ever wrote that, But when left out the oil will bypass the oil filt once the filter is full and go the path of least resistance so it can not affect oil pressure !! DON'T BELIEVE ALL YOUR READ!!!!!!!!!!!!!

Here is one of the debates on this subject.
http://forums.corvetteforum.com/c1-a...blem-saga.html

Here is another thread on this subject from some expert engine builders.
http://speedtalk.com/forum/viewtopic...er=asc&start=0