Oil System Questions and Low Oil Pressure Help

[SLeeper]

Advanced questions at the end of the post.

This in an early model Chev Small Block

- Bought a short block. Block prepped by shop and hot tanked.
- Rebuilt entire engine. Starts fine, but only 10-20 PSI oil
pressure at any RPM.
- Bought new oil pump and pump driveshaft (all aluminum).
- Primed pump
- Installed pump...oil pressure still 10-20 PSI
- Oil pan dipstick reads full!

Used assembly lube on the main and rod bearings; used assembly
lube on the lifters and camshaft. The cam bearings where installed
by the shop, I did the main and rod bearings.

http://members.rogers.com/tdese739/i...ainbearing.jpg
http://members.rogers.com/tdese739/i...ingphasing.jpg
http://members.rogers.com/tdese739/i...ngphasing2.jpg

Clearances:
Bearing clearances = 0.0015" - 0.0025"
http://members.rogers.com/tdese739/i...ugemaincap.jpg


The oil sender bore behind the intake next to the distributor,
the oil pressure gauge is mechanical (I have tried two gauges).

There is oil and air in the tube. Should it be all oil, or is
it fine to have air spaces in the line?

http://members.rogers.com/tdese739/i...lgaugeface.jpg
http://members.rogers.com/tdese739/images/oilline.jpg


Using 10W30 at the moment. Motor has been run for 15-30 seconds
for each test. With old oil pump, twice...with new oil pump once.
15 seconds on, sits for a couple of days. Repeat test once part
has been changed.

#1. What is the oil path from oil pump to pan?

Oil pump, oil filter, crankshaft bearings, rod bearings
pistons, cam bearings, lifters, pushrods, valvetrain, drain
to pan?

#2. Is the oil pressure gauge reading pressure from the pump after
the oil filter...or possibly after the cam bearings?? In other
words, is the gauge reading from a "parallel" port off the pump,
or is it grabbing from the middle point of the oil path.

#3. No oil squirting to rocker arms. How long ins seconds should it
take to get oil to the valve train? What would block the oil from
getting there?

#4. What is causing the low oil pressure? Purge air in block oil passages?

The engine block is dry...lifters not pumped up yet, oil not fully
throughout oil passages?

Not running motor long enough to to get full pressure?

#5. What is proper pressure for such a motor? 10 PSI per 1000 RPM?

Any insight is VERY appreciated.
Thanks,
Tino

[385LT1]

your mistake was using assembly lube on the lifters, this most likely clogged the oil port's in the lifters..

why would this cause your gauge to read a low pressure..?




Isnt your oil pressure sending unit at the highest point on your engine?

To prove my theory correct, isnt there a plug to an oil pressure port above the oil filter housing on the block? tap into here with your oil pressure gauge... and i bet you get normal oil pressures.





solution... let the engine run untill it gets the assembly lube hot enough to work its way through the engine... your oil pressure should start to rise... after heat is built up in the motor and oil...
heat breaks the assembly lube down.

[SLeeper]

Thanks for the reply.

I'm a little confused as to how assembly lube on the lifters is
causing a problem?

The lube is a red oily fluid, much thicker than oil, but recommended
for cam installs.

I've used it before on many top end rebuilds (this being my fifth).

I will try tapping into the block near the filter...

Any more ideas - keep them coming!

[385LT1]

Originally posted by SLeeper
The lube is a red oily fluid, much thicker than oil

[Joe 1320]

Normally, assembly lube is only used on the foot of the lifter. First, you would coat the lobes on the cam before sliding it into the block. The lifter would be submerged in a container of oil and the lifter body pumped a few times to purge any air and completely fill the body with oil. I am curious if the filter may be plugged.

[SLeeper]

Ok, that must be the problem. I just ran the car up to temp,
but still no pressure.

Took it up to 4000 RPM, just doesn't give me more than 20 PSI.

I will change the oil filter as suggested and continue to break it
in.

I guess the only thing I have to worry about now is the roller
rockers and valve tips...there is some assembly lube on the
valve stems and roller rockers. Hopefully there wont be any
damage due to lack of oil.

[385LT1]

Originally posted by SLeeper
Ok, that must be the problem. I just ran the car up to temp,
but still no pressure.

Took it up to 4000 RPM, just doesn't give me more than 20 PSI.

I will change the oil filter as suggested and continue to break it
in.

I guess the only thing I have to worry about now is the roller
rockers and valve tips...there is some assembly lube on the
valve stems and roller rockers. Hopefully there wont be any
damage due to lack of oil.

At even 20 psi of oil pressure the rockers should be getting oil..

what would keep the rockers from getting oil?


oil is supplied to the rockers, from the lifters through the pushrods.

how did the pressure check out at the oil filter housing?

[385LT1]

3952301 GM PN LT1 Oil filter adapter

comes with a pressure sensative oil bypass valve , in the event of a clogged filter the bypass valve will allow oil to bypass the oil filter all together, un harming engine operation.

[Joe 1320]

Originally posted by 385LT1
At even 20 psi of oil pressure the rockers should be getting oil..

what would keep the rockers from getting oil?


oil is supplied to the rockers, from the lifters through the pushrods.

how did the pressure check out at the oil filter housing?

Listen to da man here......

[SLeeper]

Thank you again...I think we have a winner:

"Rear main cap oil restrictor plug NOT installed"

From another board I learned that low oil pressure can be caused
by not installing an oil restrictor plug located at the rear main
bearing cap.

Without this plug, oil is not directed to the oil filter.

This is a big slap in the face for me...a good eye opener and a lesson
learned.

This would be my third "full" engine rebuild - but this is my first
rebuild receiving a block that did not have core plugs or an oil
restrictors installed.

Due to lack of experience, I had no idea about this plug. If I had
only received this answer two days earlier, I would have installed
the plug while swapping oil pumps.

Hopefully this post will help others avoid a sticky situation.

As for me, once I get over my frustration, I'll jack up that motor
and drop the pan once again. Another 5 hours of work and this
beast will be on the streets.

[raul.garcia]

Oil Pressure

Sleeper,

A bad oil filter (even if it's new) can also cause a constant low oil pressure. When I first fired up to break in the cam, the oil pressure pegged at 40 psi on a maual gauge at idle and throughout the 2000 rpm range. I also though it was the restrictor plug, my builder assured me that it was installed and that he had tested for pressure, and recommended changing the filter (Kendall) first because he'd had three other failures where the filter was the culprit.

[SLeeper]

Thanks Raul,

I already tried that before I pulled the pan again. It turns out
is was the oil restrictor under the main cap.

My car is back on the road as of today!

I started another thread yesterday with the good news.
If you're into videos, pics and exhaust sound, check there tonight.