Low oil pressure... Cam specs on 305?

[kelseydum]

Pressure seems okay when warming up but drops when it is fully warmed up. I can't hear any knocking, no metal in the oil, and the oil pressure gauge is good. My problem is when I bought the motor the guy said it was a 350 with maybe 9k miles (said it was a crate motor, but I'm not so sure now). I finally looked up the numbers on the block and it turns out to be a 305. I really don't care about that part but I put a beefier cam in it (thinking it was a 350) and am wondering if I have too much lift for stock 305 valves, rocker arms, push rods etc. Any ideas? I'm going to cut open the oil filter tomorrow and see what's inside.

I put a Mellings cam with the following specs:

Cam Lift
INT. .298
EXH. .298

Valve lift
INT.447
EXH. .447

Lobe CTR
INT. 110
EXH. 118

Lash Hot
INT. HYD
EXH. HYD

SAE Duration
291 INT.
291 EXH.

.50 Duration
223 INT.
223 EXH.

SAE Timing
BTC 30

 

[sneakysnake]

Bearing space is what creates or lack of oil pressure.Crank mains, rod journals and cam bearings, the more slack there is the less pressure there will be.Did you change the bearing with the cam?Proper oil is important too.Sounds like you may have more wear than was admited seeing how the size was wrong too.

 

[Torch]

increasing your lift and duration actually are a crutch for small valves. it makes them breath better.
what can negatively affect an engine is too much overlap for the rpm range your running in and the timing ie when the valves open, rather than how far and how long.
if you have a cam timed to make power from 3000 to 6000 rpm and put it in an engine that can't breath past 3000 rpm...that's where you end up with a problem.
the engine has a sweet spot in the resonant frequency at which the cylinder is getting a max fill, and the exhaust is being released such that when the piston starts to come up it doesn't have to push against high pressure exhaust because the exhaust has already escaped.

The timing is far more influential on run quality than the lift and duration.
Think timing=where in the rpms the power is made
And lift+duration = how long and far the valves are open, is it enough to let the max flow of the carb, intake, and ports through at the speed you'r running the engine at.

Your cam doesn't look too radical, looks like an rv cam Don't worry about it

 

[Torch]

smallblock chevies they say are good for up to .50 lift with stock rockers and pushrods. your springs should match the cam. if you get valve clatter at upper rpm's your valvetrain is bouncing around from weak springs. Machine shops can check the installed pressure of the springs and compare it to the cam specs.
often on an older engines during a standard overhaul they shim the springs to bring the pressure back up instead of using new ones.

 

[Torch]

You didn't say how much it drops...whats the pressure is when its cold and warm?
as long as you have at least 25#-30# your alright on alot of engines

when the oil warms up it slips through the clearances easier. pressure always drops when it warms up.

You can roll in a set of new crank and rod bearings as a maintenance procedure. No machine work necessary If the crank is still smooth. cam bearings are cheap you don't have to tear the whole engine down and rebuild it to do that.

My new 454 ran 80 psi cold and 60 psi warm same as my pontiac 400's I've had
My 13 liter MACK ran 60# cold and 30# warm
My ford pickup...its over here on the guage then it's over there...I don't think they want me to know.

 

[kelseydum]

Thanks sneakysnake and Torchmann, I'm going to take it over to a buddy's and get it on his lift. We're just gonna pull the oil pan first and cross my fingers it's just the oil pump or pick up tube that's failing. I was also told to see if any cam bearings were nicked when the cam was put in. I'll probably have him help me check the timing as well.

Thanks for the help. I'll let ya'll know what the problem is and how we fix it.

 

[sgtpontiac]

I know I'm a bit late on this one but...

In the mid 80's the 305 and some other motors from gm used mixed bearings front to rear on the mains.... apparently to save having to waste cranks so they would simply regrind the bad journal undersize and put it back on the line....... I ran into a number of 305's that had a 10 under front main bearing and 3 standard bearings and then a 20 under rear main.... if they throw standard bearings into it the oil pressure will drop like a stone as it warms.... also had a real problem with front main bearing knocks from putting standard bearings in where it needed a 5 or 10 over bearing..... also, sub standard oil pressure.... the factory even allowed the gm tech's to "shim" a main bearing if the journal was only a couple thou undersize... i.e. brass shims... it worked by sure wasn't right.....
I would think that most of these would be gone or fixed by now but you never know what's lurking out there wait....
Sneaky is right....normally it's bearing clearance issues that cause poor oil pressure.... JMHO.....

 

[STEVE1103]

Oil pressure

Friend had a 350 in his 47 Merc, had oil pressure when started but would fall off fast, guy who had engine, told us he took out a sold lifter cam, didn't change the bearings, we found our oil pressure problem!

 

[Old Iron]

If you really want to wake a small bore engine up, after you find the oiling problem, advance the cam 4 degrees then check the intake valve to piston clearance, on the number 1 cylinder at 10 deg after top dead center (of crank rotation).
If you have at least .080 then you're good to go.
If the valve to piston clearance is less than .080 then only advance the cam 2 to 3 deg until the .080 is achieved.

This will increase the cylinder pressure, torque will come in earlier and you will really like the increased bottom end. [dr

 

[HOT40ROD]

How low does the oil pressure go? I seen a lot of engine idle at 10-15 lbs when warm and go up to 40-50 lbs at higher rpms.

 

[old28]

oil pressure

Like HOT40ROD said about the high & low oil pressure. I have a well used 350 out of a 70's truck that we stuck in my old school 29 RPU and I have the same problem. Motor runs great, no oil leaks or smoke from lakes headers. When I start car 55# oil pressure, when it is warm and I am driving it will run 35-40#, at stop sign at idle it drops to 10-15#. No bad sounds and I think it has some bearings that need attention. What say out there?