I never understood excess cranking of the engine to achieve oil pressure. What takes the starter motor 30 seconds to do, takes a running engine about three seconds.
ALL the prelube has been done at engine assembly.
From what I’ve read and understand, the priming debate most likely started years ago because someone used an oil primer like this one from Moroso #62200:
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If you only changed the oil pump, this primes the oil pump well and you’re good to go. If you need to prime more than the oil pump, using that style primer in a SBC leads to this:
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This area is normally sealed when the distributor is installed, which has a groove to allow for oil to flow to the passenger side oil and those lifters, pushrods, etc. If the distributor is removed to prime the engine, you’ll need to use a priming tool. But be careful, notice the Speedmaster difference:
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Make sure you have a priming tool that lines up properly to seal the oil galleys or make one from an old distributor.
Mahle Clevite recommends: Preferred method: remove the distributor and use an oil pump priming tool while manually rotating the engine by hand. (Mahle Engine Break-in Procedures: page 2 under Prestart Checks & Procedures)
Mahle Clevite TB-2071: Because oil must be present in the bearing clearance space in order for the shaft to build an oil film, pre-lubricating an engine before initial start-up is extremely important. Actually pumping oil through the engine’s oil galleys is the only effective way to pre-lubricate the engine. This can be done on some engines by actually driving the oil pump with an old distributor shaft in an electric drill.
Bearings need a hydrodynamic wedge to keep the crankshaft and camshaft from touching the bearings. Assembly lube does not create a sufficient hydrodynamic wedge for this, using the correct viscosity oil creates a proper hydrodynamic wedge.
Assembly lube is used to keep the parts lubricated while you’re assembling the engine (Installing pistons, degreeing the camshaft, setting lash, etc). Ideally, most of the assembly lube gets washed off the bearing surfaces during priming as it does a poor job of protecting the bearings once the engine fires and are under load.
(FYI - For a flat tappet cam, preferably use one that’s been nitrided. Either way, use a calcium sulfonate complex grease for the lobes and don’t worry, there won’t be enough oil pushed past the lifters during priming the engine to wash it off.) (PSA – Never mix greases, the soaps used in different greases may not be compatible and wash each other out, effectively leaving no grease on the part.)
I think this debate originally arose from someone using the wrong priming tool, add in some Narcissism, lack of knowledge about hydrodynamic lubrication, and you have (a VERY CONFIDENT person saying, VERY CONFIDENTLY) “I primed the engine for infinity, burnt up my drill, and never got oil at the rockers” or “Priming is overrated, prime for X amount of time and you’re done, that’s why god made assembly lube, I’ve been doing it that way for X# of years” or “XYZ Company, and aftermarket short block suppliers are idiots to recommend this, it’s a waste of time.”
We’re hardwired to believe someone who talks confidently (regardless it’s actual knowledge or just narcissism). If somebody says something VERY CONFIDENTLY, people will tend to listen to them, and those that don’t know will also believe them. And then this incorrect information gets passed along by well-meaning people.
That’s my best guess as to why this debate seems to come up repeatedly.
At the end of the day, if I’m installing an engine, and something happens, I prefer to be able to say:
“I followed the install recommendations of AERA, Chevrolet, and Mahle Clevite.” Not:
“I did it the way SoAndSo said to”
On that note:
The OP was installing an engine from a builder that forgot to install the rear cam plug, I wonder if he got his ECU programmed and fired it up?