Posted by Vaughn [172.69.140.186] on Wednesday, May 15, 2024 at 09:24:12 :
I've looked through the manuals of both Military and civilian and none of them say to prime the pump before installation, just install a new gasket and O-ring if you've disassembled for cleaning and inspection, they don't even say lube the parts on reassembly. Ok, some of us say, if it's not primed it will suck air. Well, it's going to suck air anyway because between the oil level in the pan and the oil level in the pump pickup tube which is the same level as the pan, there is air between that level and the pump. So, the pump is first going to suck air as it sucks up oil and that air gets pushed through the engine prior to the oil. So now what happens when I shut the engine off, the oil is going to drain out of the oil passages and back to the pan and that means it will also drain from the pump and be replaced by air, there is no check valve at the bottom of the oil pump pickup tube, so the process will repeat itself the next time you start the engine and that is why there is a slight delay between when the engine starts and seeing the needle move in the oil pressure gauge. The engine will not stay pressured up, but it will be lubed.
If you�ve done a good job applying assembly lube during the engine assembly, you have nothing to worry about when doing the initial startup of an engine, the lube will protect parts until the pump supplies oil, that�s the purpose of the lube. I�ve rebuild several engines and never primed the pump, never had a problem with oil pressure on initial startup, but if the pump does not produce pressure in 5 seconds or so, you need to shut down and look for a reason, repair it, and wait several hours before attempting to start it to allow parts to cool down, especially the cam and cam bearings.
If you want to prime the pump, by all means do it, it just is not something that is a must. Images at the link of instruction and engine oiling.
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