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Old 09-25-2017, 02:57 PM
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New Chevy 350 Low Oil Pressure (?)

Newly built chevy 350 crank ground 10/10 under, solid flat tappet cam (if this has any effect on oil pressure) at idle (700-900 rpm) about 5-7 psi, cruising at 60 (2400 rpm) approximately 35-45 psi. Cold start 55 psi with 10w30 conventional oil. Cruising pressure doesn't bother me but the idle pressure does. Is this normal and do the solid lifters have an effect on it?

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Old 09-25-2017, 03:44 PM
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Quote:
Originally Posted by EragonSuperH View Post
Newly built chevy 350 crank ground 10/10 under, solid flat tappet cam (if this has any effect on oil pressure) at idle (700-900 rpm) about 5-7 psi, cruising at 60 (2400 rpm) approximately 35-45 psi. Cold start 55 psi with 10w30 conventional oil. Cruising pressure doesn't bother me but the idle pressure does. Is this normal and do the solid lifters have an effect on it?
Especially Chevy's before 1987 have low idle oil pressure, one reason why high volume, high pressure pumps are so common with rebuilds. From a functional stand point this can also be a sign that the main and/or rod bearing clearance is too wide. The pressure below that of the pop off valve on the pump is a function of how much oil (volume) the pump can pump divided by how much oil escapes the bearing clearances. You can test this by using a heavier viscosity oil which should increase the pressures your seeing. The cam and lifters can contribute but that between solids and hydraulics that is very minor unless the lifter bores are worn out increasing clearance around the lifter in which case that's another leak pressure leak in the system.

Your pressures look pretty normal for an SBC with a stock pump. That said do you know what the main and rod bearing clearances measured for this engine?

Bogie
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Old 09-25-2017, 04:15 PM
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Solid lifters won't change anything as compared to a hydraulic.

Reason for the low pressure is excessive clearance somewhere....main or rod bearings, cam bearings, lifter bore to lifter body clearance too large, distributor body lower section to block clearance too large are the 4 main places pressure gets lost by way of excessive bleed-off.

What were the actual rod and main bearing clearances??

Was lifter to bore clearance verified??

Standard volume or high volume pump??
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Old 09-25-2017, 04:50 PM
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Quote:
Originally Posted by ericnova72 View Post
Solid lifters won't change anything as compared to a hydraulic.

Reason for the low pressure is excessive clearance somewhere....main or rod bearings, cam bearings, lifter bore to lifter body clearance too large, distributor body lower section to block clearance too large are the 4 main places pressure gets lost by way of excessive bleed-off.

What were the actual rod and main bearing clearances??

Was lifter to bore clearance verified??

Standard volume or high volume pump??
first question: never checked actual clearances
second: nope
third: standard volume
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Old 09-25-2017, 04:55 PM
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Quote:
Originally Posted by BogiesAnnex1 View Post
Especially Chevy's before 1987 have low idle oil pressure, one reason why high volume, high pressure pumps are so common with rebuilds. From a functional stand point this can also be a sign that the main and/or rod bearing clearance is too wide. The pressure below that of the pop off valve on the pump is a function of how much oil (volume) the pump can pump divided by how much oil escapes the bearing clearances. You can test this by using a heavier viscosity oil which should increase the pressures your seeing. The cam and lifters can contribute but that between solids and hydraulics that is very minor unless the lifter bores are worn out increasing clearance around the lifter in which case that's another leak pressure leak in the system.

Your pressures look pretty normal for an SBC with a stock pump. That said do you know what the main and rod bearing clearances measured for this engine?

Bogie
Clearances were never measured because this is my first ever build and I learned as I went. That said, the man at the machine shop asked me "race tolerances or stock?" and I told him stock. Btw this is a 1990 block in a 1978 GMC truck
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Old 09-25-2017, 05:19 PM
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As long as pressure comes up quickly to 15-20 lbs by the time engine rpm hits 1100-1200 rpm, you'll be just fine.

If you don't like the low pressure at idle, it bothers you too much, then your easiest fix is a high volume pump.

10W40 will help a little, 20W50 even more, but probably not more than 5-8 lbs.

Sounds like you just learned,.. even if you trust your machinist, check his work, even if it is just Plastigauging all the main and rod bearings.....Plasticgauge readings on the slightly high side could have lead you to making the decision to swap to a high volume pump during your initial assembly.

Live and learn
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Old 09-25-2017, 06:34 PM
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Quote:
Originally Posted by ericnova72 View Post
As long as pressure comes up quickly to 15-20 lbs by the time engine rpm hits 1100-1200 rpm, you'll be just fine.

If you don't like the low pressure at idle, it bothers you too much, then your easiest fix is a high volume pump.

10W40 will help a little, 20W50 even more, but probably not more than 5-8 lbs.

Sounds like you just learned,.. even if you trust your machinist, check his work, even if it is just Plastigauging all the main and rod bearings.....Plasticgauge readings on the slightly high side could have lead you to making the decision to swap to a high volume pump during your initial assembly.

Live and learn
I always tell myself that if I don't learn something every day I've given up. Well today I sure learned something. I'm not terribly worried just because my cruising pressure is so good but sometime I might stick a high vol/high pres pump in.
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Old 09-25-2017, 07:25 PM
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Quote:
Originally Posted by EragonSuperH View Post
I always tell myself that if I don't learn something every day I've given up. Well today I sure learned something. I'm not terribly worried just because my cruising pressure is so good but sometime I might stick a high vol/high pres pump in.
I'd just kick it up to a 15-40 or 20-40 till deepest darkest coldest winter then go back to 10W-30 till the weather warms up again then back to 15W-40 or 20W-40.

Bogie
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Old 09-25-2017, 08:10 PM
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I'm with Bogie, if 15w__ or 20w__ picks up your idle oil pressure, then you'll know that a high volume pump will resolve your issue when using lighter weight oils. And don't fool yourself into thinking the heavier oil is a permanent solution - it's more of a band aid IMO. But at the moment I'd swap over to 20W50, see what happens, and make a plan from there.

Also, Eric is correct, if the pressure increases to 20+ with a minor rpm increase, then all will be well, but it's unnerving (to me) to run around at sub 10psi.

If you end up swapping out the pump, then that is a great time to plastigage the bearings.
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Old 09-25-2017, 08:44 PM
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Quote:
Originally Posted by 64nailhead View Post
I'm with Bogie, if 15w__ or 20w__ picks up your idle oil pressure, then you'll know that a high volume pump will resolve your issue when using lighter weight oils. And don't fool yourself into thinking the heavier oil is a permanent solution - it's more of a band aid IMO. But at the moment I'd swap over to 20W50, see what happens, and make a plan from there.

Also, Eric is correct, if the pressure increases to 20+ with a minor rpm increase, then all will be well, but it's unnerving (to me) to run around at sub 10psi.

If you end up swapping out the pump, then that is a great time to plastigage the bearings.
Was planning on swapping the pump hopefully with the motor still in place, but I suppose plastigaging is possible then too
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Old 09-25-2017, 11:13 PM
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Machine shops sometimes grind crankshafts on the high side of clearances because they don't know how the car will be used, no matter what the customer says.

That is called the machinist's CYA program and they will micro-polish the crank journals accordingly. The machinist does not want any come-backs in case the customer takes the engine to 6,000 RPM on the first day out.

Your engine may have as much as .0035" clearance on the main journals, .0025" clearance on the rod journals and .020" - .028" Rod side clearance per pair.

That will not be a problem.

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Old 09-26-2017, 08:17 AM
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This being a 90 engine with better from the factory clearance and tolerance on the machined parts than earlier versions probably lost that when the journals were turned and is now a bit looser than one would expect. Also, I could see that if the original oil pump was reused it is worn perhaps even with scratches from debris that circulated over the years to where internal leakage from this has reduced its output which is a good reason itself to replace the pump with the rebuild. But at this point I'd just mess with oil viscosity to bring up the idle pressure. Unless you pull the engine, opening it up to replace the pump often invites oil leaks from the pan rail, the SBC not being the easiest thing to keep oil in.

Bogie
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Old 09-26-2017, 10:16 AM
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Machinist's motto on Crank and Rod Bearing clearances:

"If too tight, everyone knows....If too loose, only you know"

If you want accuracy, don't use a plasti-gauge.. Professional engine builders use a snap gauge and micrometers. A plasti-gauge cannot measure journal taper which is a result of inaccurate crank grinding. If you want to measure if journal taper exists, the plasti-gauge measurment should be taken at least twice on the same journal.
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Old 09-26-2017, 10:26 AM
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Quote:
Originally Posted by BogiesAnnex1 View Post
This being a 90 engine with better from the factory clearance and tolerance on the machined parts than earlier versions probably lost that when the journals were turned and is now a bit looser than one would expect. Also, I could see that if the original oil pump was reused it is worn perhaps even with scratches from debris that circulated over the years to where internal leakage from this has reduced its output which is a good reason itself to replace the pump with the rebuild. But at this point I'd just mess with oil viscosity to bring up the idle pressure. Unless you pull the engine, opening it up to replace the pump often invites oil leaks from the pan rail, the SBC not being the easiest thing to keep oil in.

Bogie
I put a new oil pump in, I'd never re-use an oil pump, too much liability riding on that one 30 dollar part to not replace it
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Old 09-26-2017, 10:45 AM
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Run some heavier oil... Something no one has asked, did you check the gauge for accuracy? Like with another gauge?
Remember too, if you only had an "idiot light" it would probably never come on. Drive it!
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