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Old 12-21-2011, 04:15 PM
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Low to no oil pressure on a small block 350

Okay guys, i have searched through tons of oil pressure forums on here and havent found my answer. so i have a 350 that was just rebuilt. i have low to no oul pressure unless its cold and it shows 20-25 psi. but when it warms up some it shows like 2 maybe none pressure. i got a new gauge and its not the gauge. also at higher rpms like before it shifts into 2nd theres a sorta loud rattle. so i was wondering why i dont have much pressure and if the rocker arms wernt tighten properly if they could be loose? i did not recheck them after the new break. and maybe a clogged pickup screen cause low pressure?

everything is new in this engine besides the crank,block and the actuall heads and rocker arms.
New valves, springs pushrods lifters,all bearings new oil pump,new noise geardrive , new lunati cam 284dur.458lift and new valve springs 0.550 in. maximum lift. installed at 1.750 in. and the pushrods are standard length
im using 5w30 and added and extra quart on 20w50 because i didnt think the HV oilpump was not getting enough oil because it was sucking so much and also thought the oil was tooo thin?

let me know if i missed something

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Old 12-21-2011, 04:20 PM
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sounds like one of the three soft plug oil galley plugs behind the timing gear is missing.. Or major bearing wear or a combo..
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Old 12-21-2011, 04:27 PM
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i know for sure the those are in because i replaced them with the new ones i got with the water plug kit and they were all tightened. and what would cause it to wear? the crank spun smoothly when inmstalled and it was torqued correctly
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Old 12-21-2011, 06:15 PM
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Quote:
Originally Posted by jaeger_bombs
i know for sure the those are in because i replaced them with the new ones i got with the water plug kit and they were all tightened. and what would cause it to wear? the crank spun smoothly when inmstalled and it was torqued correctly
Were the clearances checked? Is the pump bolted on tight? is 25 psi all you can get out of it? Did pickup fall off? you say you have a HV pump, did you reposition the pickup correctly from the bottom of the pan? Is it new pump or old pump with stuck relief valve? I can check that pump for you and tell you what the relief valve is set at.
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Old 12-21-2011, 06:28 PM
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yeah the clearances is fine, pump is on tight because i had to redo the rear seal because it was crappy, and the pump is brand new so the only thing it might be would be the pickup tube, ima drop the pan and make sure its all cleaned out and make sure its reposition right
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Old 12-21-2011, 06:56 PM
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Every time I've had an oil pressure problem with an engine it has always ended up being too much clearence. I had one V6 engine that I spent a chunk of money on at the machine shop with the block being bored,crank turned new pistons pressed on the reconditioned rods and new cam bearings installed. Everything in the engine was good as new when I put it back together, so I didn't worry about using plasti guage on the crank or rod bearings. It was doing the same thing yours is. It would hold oil pressure for a few minutes and then drop to almost zero.
I tore it back down like 3 times myself and then took it to a friend of mine and he did the same thing and couldn't figure it out. The fourth time I took it apart it had been ran enough to notice a little wear on the outside of all the crank bearings. I took the bearings back to the machine shop and had them check the thickness with a bearing mike and they were standard bearings and the crank had been turned 10/10. I had gotten all the parts from the machine shop that did the work, so he made good on his mistake. It must have been a pretty cheap overhaul kit because there weren't any markings on the bearings and I still don't remember if the box they came in was marked correctly or not. Just goes to show, that anything can go wrong and will somethmes.
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Old 12-21-2011, 07:33 PM
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Quote:
Originally Posted by jaeger_bombs
Okay guys, i have searched through tons of oil pressure forums on here and havent found my answer. so i have a 350 that was just rebuilt. i have low to no oul pressure unless its cold and it shows 20-25 psi. but when it warms up some it shows like 2 maybe none pressure. i got a new gauge and its not the gauge. also at higher rpms like before it shifts into 2nd theres a sorta loud rattle. so i was wondering why i dont have much pressure and if the rocker arms wernt tighten properly if they could be loose? i did not recheck them after the new break. and maybe a clogged pickup screen cause low pressure?

everything is new in this engine besides the crank,block and the actuall heads and rocker arms.
New valves, springs pushrods lifters,all bearings new oil pump,new noise geardrive , new lunati cam 284dur.458lift and new valve springs 0.550 in. maximum lift. installed at 1.750 in. and the pushrods are standard length
im using 5w30 and added and extra quart on 20w50 because i didnt think the HV oilpump was not getting enough oil because it was sucking so much and also thought the oil was tooo thin?

let me know if i missed something
Just because a gauge or sender is new doesn't mean it works correctly. Put another sender and gauge in there for an independent check (different brand, different type). New these days with all the imported parts doesn't mean much, maybe never did. Anyway do the simple thing first.

The internal reasons are several including the use of a high volume pump. Now don't get me wrong about HV pumps I use 'em myself; but the bypass on these things can be trouble-some to where the bypass is stuck full open, or since the return passage is an internal to the pump loop back to the intake side, they can interfere with themselves on the intake side. There is always the possibility that the intake is leaking at the pump which would allow the pump to draw air in addition to if not in favor of oil.

Of course there's always the leaking galley plug possibility. Or the distributor isn't seated correctly as on the Chev, at the base of the distributor is a groove for the right side lifter galley. A miss located distributor can open a pretty big hole at this spot allowing oil to just flow back to the pan otherwise unused.

Bearing clearances that are too wide will drop pressure, they could be carved out by pieces of metal that came off the push-rods or else where because of the rocker arm maladjustment. Though with a HV pump it's hard to imagine no pressure even if the bearing shells were missing. Anyway, what were the clearances.

Anyway back up the gauge reading first with an independent gauge and sender before going nuts, there'll be plenty of time for that if it gives verification of poor pressure.

Bogie
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Old 12-21-2011, 07:33 PM
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Quote:
Originally Posted by 41'srfun
. The fourth time I took it apart it had been ran enough to notice a little wear on the outside of all the crank bearings. I took the bearings back to the machine shop and had them check the thickness with a bearing mike and they were standard bearings and the crank had been turned 10/10. I had gotten all the parts from the machine shop that did the work, so he made good on his mistake. It must have been a pretty cheap overhaul kit because there weren't any markings on the bearings and I still don't remember if the box they came in was marked correctly or not. Just goes to show, that anything can go wrong and will somethmes.
I ve seen that before. Plus O/P said it knocked or something. I think you are on to something.
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Old 12-21-2011, 09:44 PM
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I was going to suggest the bearing clearances. You will only not check these clearances once when you are a "flat rate mechanic". Getting bit like this will cost you a weeks pay real quick in a come back. Maybe a lot more in a lost customer.
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Old 12-21-2011, 09:59 PM
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I had a similar issue with a SBC. It turned to the builder installed the rods backwards i.e #1 was in #2 bore all the way through. I also checked the crank journals and they were not perfectly round. The rod bearings were worn through the bi-metal surfacing down to the base metal in spots.
That was the last time I trusted what the machine shop or the builder said.

Hope you find the problem but it will require tearing the motor down to find it.
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Old 12-22-2011, 12:55 AM
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You can check the rod journal and crank journal clearance's with plastigauge. I mention plastigauge cause it's so cheap and fool proof to use. Ever used it ? It's a wonderful item to make sure your .010" under journals are not met with standard bearings.. I'd bet you have std mains with your 10/10 crank. Make sure when you open it up that it's not been exposed to heat and left a stripe down the paper.

The rattle at shift worries me, I'd park it till you get some pressure.

I have seen engines exhibit this issue with extreme debris in the oil passages, good pressure cold, zero when hot.

I wonder if the machinist rodded out all the oil flow passages ? This is a must-do on any engine rebuild, even if it was 'hot-tanked' the chances of blockages are great.

Pull the plug next to the water pump above the timing cover and check it there, it's easier than the one next to the distributor, use a mechanical gauge for industrial stuff to be sure, they are cheap. The fitting is 1/8" pipe threads on the engine.

You didn't mention if it's in a truck or not, but if so, sometimes the external oil cooler and lines seem to cause issues with pressure. Don't laugh, on a pals 92 full size 350, his pressure went from near none to over 30 when he blocked off the cooler.

Did you check the drain-back holes in the heads ? Those can stop up easily and show zero pressure. Are you running roller rockers ? Most guys limit the oil to RR's to keep it down below where it's useful.
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Old 12-23-2011, 08:30 PM
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Sounds like bearing clearance to me, but the real question is whether it was wrong sized bearings, crank turned wrong size, or debris in the engine from rebuild that washed out the bearings.
I'd certainly pull the pan and inspect visually, then pull one set of bearing s to check the back side for part numbers and size. They should be stamped for what undersize they are, so if you know what the crank was turned to you can verify the bearings. At the same time if it looks OK you can plastigauge the bearings to see how things are presently.
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Old 12-23-2011, 10:35 PM
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Ok. My dad has said time and time again that the clearance is in spec. The last time I started up I didn't get anything whatso ever so I replaced the pump and pickup screen and the turned the oil filter "bracket" around and started it up. And got around 20 at cold and look like it droped to 3 psi at around 150deg. (couldn't tell exact psi but it was showing more than zero.) The crank wasn't turned because he said they were smooth and not grooved so we just put the crank In this different block and put new bearing throughout the whole block. All std. And I know for a fact that all the galley plugs are in, new std volume/pressure pump and new pickup screen set to right depth. What could it be? And also a question, is there a small thin silver washer on the distributer that sits between the intake man and dist. That could cause the oiling problem? I know it sits flat on it right now but maybe its to far in?
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Old 12-23-2011, 11:11 PM
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The crank being "flat and smooth" does not mean the journal has the correct tolerances. How did you/he measure or check it to be sure it's within spec? If it was checking visually, then you should go back and plastigauge it, then determine if it's just smooth and nice, or too loose and not letting pressure build.
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Old 12-24-2011, 06:43 AM
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I have original Covette engine in the shop and the mains from the factory are .009 under so everything needs to measured!!

Also I have a 400 block that was built and for 1000 miles it had low oil pressure knocked it apart the center cam bearing had spun ant looked like the origanl builder used stock cam bearings where a performance set should have been used.
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