Another answer: With the spark plugs removed and the engine turning over with the starter motor, there is only pure rotation of the crankshaft without loading up the main and rod journal bearings. That should not harm any internal parts before the oil pressure picks up.gahorn wrote: ............But... let me ask the question.... : What's the difference between letting the starter motor turn the engine until oil pressure is indicated.... versus simply starting the engine and letting oil pressure develop?
Answer: The second method is easier on the starter motor, and gets the upper cyls lubricated sooner.........
When oil pressure does pick up, the pressurized oil film prevents metal to metal contact between the journal bearings and the crankshaft and the engine is ready to be started. If oil pressure does not pick up quickly, no harm would be done.
If the engine is started dry and allowed to run, each power pulse will grind metal to metal contact between the crankshaft and the main and rod journal bearings, possibly wiping out the bearings if the oil pressure does not instantly pick up, which does happen.
I would not be nearly as worried about the lack of upper cylinder lubrication or being easy on the starter motor as I would be about metal to metal contact between the crankshaft and main and rod journal bearings before the oil pressure picks up.
Agreed! The absolute best way to pre-oil is with external methods without rotating the engine.gahorn wrote: A good method to get oil pressure to "exist" before first engine-start is to pressurize the oil galleries with a grease-gun filled with' engine oil fed into the galleries............