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Old 10-11-2018, 08:22 PM   #1
cst350
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No Pressure

OK, I am at my wits end. My truck is/was at a point that the “builder” motor that I was running was underpowered for what I wanted. I went out an found a nice high nickel 4 bolt SBC block and sent it to one of the best engine builders around. I had it clearance for a 383 crank and bored .30 over. Scat rotating assembly putting it to @ 10.1. I then put on a set of AFR heads with the same shop doing a 3 angle valve job to freshen them up (even though they were never raced) I am running a Comp XS282 Solid lifter cam. I also put in some Howard Cams EDM lifters (91118) and 8/200 push rods. Melling M55HV pump with a 7 quart pan. The pick up is a bolt on from Kevco and is 3/8” from the bottom of the pan. I plastic-gauged the crank bearings and they were all within tolerance. If any thing they were a bit tight.

After using Royal Purple breaking for @ 30min I drained the oil and replaced it with Lucas 20/50. When I fire the motor it has between 25 and 30 lbs of pressure cold. After getting up to @ 180 deg the pressure drops to almost nothing! If I drive it around the block the pressure comes up a bit (12 lbs. at 3,000 rpm) but no where near what I would call safe. The engine temp never gets above 200. I swapped the distributor and nothing changed. I tried a different gauge and nothing changed. I probed down the oil gauge hole to double check that the main bearing had the oil plug in place and it does.

Thinking maybe I should ditch the EDM lifters for traditional ones as one last Hail Marry. Other than that I guess I have to pull it. First I would check to see iff the 3 oil plugs behind the timing gear are there… then take a look at the oil pump to be sure the relief spring didn't stick.

Anyone with other suggestions before things get out of hand $$$?
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Old 10-11-2018, 08:37 PM   #2
hjewell2
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Re: No Pressure

What was pressure during break in period?
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Old 10-11-2018, 09:55 PM   #3
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Re: No Pressure

The engine sounds like a very nice combo. If it was me I would try another oil pump, especially if I can get the oil pan off fairly easy. You could have gotten the .01% defective oil pump. If nothing changes with another oil pump then it must be the lifters. I have never used EDM lifters but I can't believe they would lose that much oil pressure. Good luck.
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Old 10-12-2018, 09:39 AM   #4
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Re: No Pressure

Electric or mechanical oil gauge? There are different sender ranges for the electrics.

IIRC -some(all?) SBC blocks have a 2nd oil tap part way down the drivers side toward the oil filter.

Double check the little threaded piece the oil filter screws onto. The install torque on those is in IN/lbs not ft/lbs. I know from experience that ft/lbs will crack that piece.
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Old 10-12-2018, 10:49 AM   #5
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Re: No Pressure

I'm sure you've already thought of it and probably done it but you could replace the oil filter with a different brand. It's the cheapest and easiest thing to do.
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Old 10-12-2018, 11:31 AM   #6
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Re: No Pressure

Break in pressure was @12-15 @ 2,000 rpm
Gauge is mechanical
I will inspect the pressure valve between the filter and block

(IIRC -some(all?) SBC blocks have a 2nd oil tap part way down the drivers side toward the oil filter.)
Could you describe in more detail? Maybe a picture?

This is an internal tap right? I have zero external leaks.

Don't know if I can drop the pan w/o pulling the motor. I can give it a try...
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Old 10-12-2018, 11:32 AM   #7
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Re: No Pressure

Yeah... on my 3rd filter.
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Old 10-12-2018, 11:42 AM   #8
truckdude239
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Re: No Pressure

there is also a core plug under the rear main cap that if not reinstalled will cause oil pressure issuses
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Old 10-12-2018, 12:35 PM   #9
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Re: No Pressure

This is the plug I verified by measuring down from the oil pressure gauge hole
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Old 10-18-2018, 07:03 PM   #10
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Re: No Pressure

Here is a trouble shooting guide from Melling.

https://www.melling.com/aftermarket-...u-k/technical/

I'm not an HV pump guy but I do like the Z/28 pump from Melling. I tried to find what the pressure on the HV pump is supposed to be but didn't easily. It ships with two springs and you get to choose high or standard pressure, correct? And I assume you have the high pressure spring installed?
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Old 10-18-2018, 07:30 PM   #11
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Re: No Pressure

Something I ran into years ago on a motor I built....

when the machine shop installed the cam bearings, they failed to get the rear bearing all the way in to the proper position....

there is a radial groove under that bearing where oil goes up around it and the up into the lifter galley......

if that groove isn't covered by the cam bearing , most of the oil will just pour out there and run back into the pan....the motor would run, just didn't have much oil pressure.

not saying that's your problem but it happened to me.
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Old Yesterday, 09:42 AM   #12
cst350
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Re: No Pressure

MikeC: yes I used the high pressure spring.

A1971 Blazer: Right now I am considering dropping the pan w/o pulling the motor as one last attempt to not disassemble everything again. If successful I should be able to see that bearing...Thanks for the tip
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