Oil Pressure Drops At 15psi On Fresh 327

30fathoms

Member
Howdy all,

I've been lurking for a while and learned a ton of useful information from this site, many thanks to everyone who have contributed their experience!

Apologies for the long post, just wanted to include any and all info which may be pertinent as to why oil pressure on a fresh 1965 327 SBC would consistently reach 15-17 psi then drop to 0-2psi. Here's "The rest of the story..."

Recently my son decided he wanted to drive the '64 C20 (with a '65 SBC 327) that I drove in high school, so we pulled it outta the barn after 3 decades for a little father-son project. When it was parked, the 80K 327 would make decent oil pressure with the original canister oil filter mount and an adapter for a spin-on, "decent" being on the right side of the half-hash on the dash gauge, never did put a numbered gauge on it.

The block got a full machine shop refresh including .030 bore. The rebuild kit came with what I would consider good components for a street motor, including Clevite bearings and a stock Melling oil pump. On assembly, the bearings plastigauge'd between .0020 and .0025 (one was tight at .0010). The new configuration included new hydraulic flat tappet lifters and roller rockers in new Summit 165 iron heads, a Comp X4 262H cam with 218 intake duration at .050, Edelbrock RPM intake and AVS2 carb, and MSD 8362 SF distributor. We primed the motor with the old dizzy shaft and drill until we got flow at the rockers,...unfortunately, I didn't pay close attention to the pressure gauge, just the flow, I know...major cranio-rectal inversion on my part.

I can find my way around 7.3L and 5.9L diesels but this is my first SBC from the ground up...so here is our problem: the motor fired right up and ran with no lifter noise or other indications of impending doom but the oil pressure would consistently reach 15-17 psi then abruptly drop off to 0-2 psi, this was at or just above idle (800-1000 rpm). We limited these runs to not heat up the block.

Trouble shooting so far included:
1) Verified oil level at just above full on aftermarket dip stick (4.5 qts. dino 10W30 in original oil pan with the pick up tube 1/2 off the bottom).
2) Fresh oil and filter after the first 4 runs, cut open filter for trash - none found.
3) Swapped oil gauges (mechanical) and tubes (used both nylon and metal lines) - no change.
4) Swapped oil filter adapters, to include one which was full flow - no change.
5) Verified the plug in the vertical oil galley, below the oil pressure adapter, was set at 8 3/8 in depth from top of block face.
6) Verified both rocker banks were getting oil and the dipstick oil level was not changing after drain back.
7) Tried both long and short oil filters - no change.
8) Pulled the distributor, gears looked new and the oil pump shaft appeared pristine.
9) Spun the oil pump with a drill cw (again) and found that when the pressure reached 15-17 psi and dropped off, the torsion on the drill would slack noticeably.

From the recent drill spin, it feels like the oil pump relief valve is just letting go at 15-17...on a fresh pump. When we engaged the dizzy shaft and spun the oil pump by hand, we could feel what I would call normal resistance to flow from the pump. We de-burred the pump and verified fit on install so the only thing I can think of is we got a weak relief spring outta the box (the pick up tube was not brazed with the spring in place). Any other trouble shooting suggestions would be greatly appreciated before we pull the pan and oil pump.
Thanks in advance,
 
well, given the stated testing Id pull the oil pan and replace the existing oil pump,
and while doing that verify the oil pump pick, up is mounted at least 3/8" above the oil pan floor
your stated symptoms would tend to indicate either the pumps defective
and\OR
the oil pump pick up tube is mounted too close to the oil pan floor,
which would result in the oil pump starving for inflowing oil,
this is very similar to the results guys get if they install a high volume oil pump and fail to verify the oil pump pick-up to oil pan floor clearance,
AND/OR
the oil pump pick-up came loose of the oil pump, or the oil pumps loose on the block
this would result in decent oil pressure up until the point that the oil level in the oil pan dropped ,
enough to allow the oil pump to suck air into the pump, as a couple quarts are now in the upper engine,
lowering the oil pan oil level.

http://garage.grumpysperformance.co...l-pressure-switch-on-fuel-pump-circuit.16013/
since the oil pump is providing 17 psi at idle and then drops pressure noticeably after a short time,
BUT it returns
to the 17 psi if a bit of time elapses its unlikely to be a loose oil passage plug
it could also be related to loose trash in the oil pan clogging the pump input pick-up that clogs the pick-up,
once the oil flow into the pick-up tube increases but comes free if the engines not running, in either case you'll need to
pull the pan, and check the oil pump pick-up to oil pan clearance with the oil pan in place,
and I would braze the oil pump pick-up to the (NEW)oil pump once that clearance distance was verified

in any case, its time to pull the oil pan and front timing cover and verify what your dealing with


PLEASE read ALL these threads
and
please take a few clear pictures ,
and tell us what you find after a detailed inspection

http://garage.grumpysperformance.com/index.php?threads/installing-an-oil-pump-pick-up-tube.1800/

http://garage.grumpysperformance.co...m-oil-pump-installed-now-no-oil-pressure.525/

http://garage.grumpysperformance.com/index.php?threads/basic-info-on-your-v8-lube-system.52/

http://garage.grumpysperformance.co...l-pumps-pressure-bye-pass-circuit-works.3536/

http://garage.grumpysperformance.com/index.php?threads/testing-a-chevy-oil-pump.6479/

ChevyOilingPluga.jpg
 
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Thank you Grumpy, I was afraid that would be the next step. The pick up should be 1/2 inch off the floor according to our measurements on install: basically mounted the pickup, pushed the pan on, then measured up 1/2 inch from one of the crank throws. So off it comes. And thanks for the links, I've read through quite a few of those and found them VERY informative.
We'll post results with some pics.
 
Update - Pulled the pan and re-measured depth of the oil pump pickup: the pan measured 7 1/4" deep from the pan flange (original pan with a shallow dent), the pickup measured 6 3/4" down from the bottom of the block, so with the cork gasket we were around 1/2" from the bottom originally. Pulled the old pump apart and the spring felt tight (not sure if one can tell manually whether one is shot) and the gears were clean with no chatter marks. Replaced a new M55, reset the pickup by taping a 3/8" drill bit to the bottom of the pickup tube and test fitting the pan...we then verified again via measurements at 3/8" off the bottom. Did another oil change and looked for trash. Found some light "dust" type particles in the oil and a few larger pieces about 1/3 the size of a piece of rock salt, both of these were non-magnetic. Unfortunately, we also found the piece in the attached pics; this was the only piece like it we recovered from the waste oil. Primed and ran the new pump with the drill getting 10-12 psi (sustained) and oil flow at both rocker banks. Fired it up for a hot second and got about 2 psi at idle and 10 psi at 2000 rpm. Based on the chunk in the pics, we decided to pop the intake off and inspect the top and bottom end. All lifters and rods articulate smoothly with a manual spin of the motor and no trash was visible in the oil which remained in the block and cylinders. We'll pop the mains off and check bearings next... thanks and fingers crossed
From oil pan 1.jpg From oil pan 2.jpg
 
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Photos at every step along the way would sure be helpful, someone might just catch something
that we are not getting with only your text.
 
Let me start by saying thanks again...and testify that one should not assemble a motor one might be unfamiliar with while distracted...I'd be cussing like a sailor at low tide if I wasn't cautiously optimistic about the bullet we probably dodged.
From the below photos, I'm sure you can see our mistake: none, yep not a single one of the front oil gallery plugs made it into the block. How in Sam Hill the thing made any pressure will remain a mystery. Pulled all the main caps and a few of the rods and did not find a single fragged bearing and we had good oil at each. I would greatly appreciate your opinion on the bearing wear in the pics. The wear pattern looks a bit narrow to me, at least 60-75% width across the mains seems right?
 

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yeah, the bearings show little wear,and can most likely be reinstalled and used without any issues.
like I suspected, once you said it never got over about 10- 12 psi, thats a MASSIVE internal oil leak,
and the most likely place is the forward oil gallery plugs having either never been installed or they blew out.

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Nothing like getting a two-fer engine assembly on the first go...really appreciate the quick replies. And I'll be waitin' for my slap down from the Okie...well deserved in this case.
 
the truth is most of us learn by watching (hopefully) more knowledgable people,
and remembering their successes and MISTAKES
and especially we tend to remember our own MISTAKES
 
Did the same mistake on my race car! The motor plate allowed 20 pounds while priming. Do you know how big a puddle 8 quarts of oil makes? Lol
 
Dont 4 get to drill a small hole in one the side plugs to spray oil on the chain(i forget the one) but someone will remember the side to drill it in?
 
I can hardly believe that this engine didn't seize without the 3 front plugs installed. :eek:
Go buy a lottery ticket NOW!
 
I can hardly believe that this engine didn't seize without the 3 front plugs installed. :eek:
Go buy a lottery ticket NOW!
We knew right away that we had an issue so we never pushed it. I'm certainly no expert on the SBC oiling system but it seems pretty forgiving.

And, thanks for the tip on the .035" hole, we'll be triple checking everything on this go'round!
 
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