This pertains to changing the timing gear/chain on a 2000 Silverado 4.8L. Where the engine previously held 40-80# oil pressure, it now will dip completely to nothing on the gauge (check pressure lights) and maximum WOT is 40 psi (which as stated was previously minimum.) Could not replacing the O-Ring on the pickup tube be the culprit?
Below is longer explanation:
Procedure:
Drained Coolant and engine oil.
Disconnected hoses
Removed Fan, Serpentine Belt, Tensioner assembly
Unbolted Water pump
Pulled balancer/pulley
Removed Timing cover
Loosened Oil pan, dropped about 1 inch
Unbolted and unhooked pickup
Removed oil pump
Unbolted Cam gear/chain
Pulled Crank gear
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And as per %26quot;directions,%26quot; reversed above procedure for assembly. We %26quot;primed%26quot; the oil pump by blocking one end with %26quot;motor (white lithium) grease,%26quot; filling with oil, and plugging the suction side with more grease before assembly.
This is where our potential mistake--and our need for more experienced help--may have taken place: We did not install a new o-ring on the pickup tube before reinsertion into the oil pump.
My father and I have a great amount of experience (racing background) with 350/400 SBC motors. None at all with the new generation stuff. After discussing this at length, we've concluded this may be the issue. But, before we tear this all back down, we'd like some more insight.
As for the GM %26quot;specs%26quot; (6 to 24#) on oil pressure, we've found that to be inaccurate. Lifter tick occurs at anything from 20psi down. It honestly doesn't clear up until 25-30#. So, although nothing that rotates is damaged, for them to spec this low psi for hydraulic (roller) lifter motors seems nonsense! This is further reinforced by the fact this motor originally held no less than 40# at any time.
The secondary question in all this pertains to the new timing set. The new assembly still allows for (from our perspective) an absurd amount of slack. From observation, this new assembly appears barely better than the 230,000 mile set it replaced! Is this common for these motors? Please keep in mind that our experience pertains to the older SBC engines, in which the chain has barely any noticeable slack.
Thank you all in advance!
JK
What would cause low oil pressure Chevrolet 4.8L after timing set change?
Re-using the old O-ring is a definite no-no. If you don't have a good seal there, the pump will suck air, and pressure will be accordingly lower. And contrary to another poster, the O-ring is not below the oil level.
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Lubricate a NEW (their caps, not mine) oil pump screen O-ring seal with clean engine oil.
Push the oil pump screen tube completely into the oil pump prior to tightening the bolt. Do not allow the bolt to pull the tube into the pump.
What would cause low oil pressure Chevrolet 4.8L after timing set change?
Sounds about right but you didn't mention what weight oil you put in. If the oil is too thick you will get lower oil pressure. I like 5W-30 as an all around good oil for normal driving.
Sound like the O ring may have moved out of place, cut, or split and now you are getting some air in system. Small air bubbles in the oil can be compressed causing lifters to collapse as pure fluid can't be compressed. A one minute shortcut could of caused you hours of extra work. Now if you ever need to prime a oil pump again just submerge it in oil and spin the gears in the pump a few times and your done, no need to plug up with grease that will slow oil getting in. The factory oil pressure spec is taken with a external gauge connected to a oil galley, not using a sending unit that is using current resistance to calculate pressure the spec is correct.
You have more experience with GM than I, so don't take this with too much weight. But I don't understand how the pickup or pump could be involved with timing chain and sprockets?
But beyond that, yes, I would worry about the pickup sucking air.
And I don't get the pump priming idea.
I understand the grease would prevent leak down, but pumps always leak down and are fine with leak down. So I would not have put grease in the pump openings. If you really want to prime, I would take the oil pressure switch our and for oil in there, under pressure. That will fill all the galleries.
I think the grease can trap air and make the pump not suck the oil up properly.
But just my thoughts.
the oring will not be the problem sounds to me you did everything right . sometimes it just take a lot of time for it to prime up. I know it gets irritating at times but from what you are saying I cant think of anything else but just keep letting it run a little more or just repack the oil pump again i have had to do that a couple of times, but on the oring deal i did the same thing once and the dealerships service manager told me that if you think about this long and hard the oring is submerged in oil anyways so he never understood why they would use them in the first place. so please get back with me when you get it going. ok
