I have seen this happen on new engines on start up a few times. Did you prime the engine real well before starting? I like to prime the engine and turn it in about 4 different spots to get the
oil through all of the passages real well. A lot of times if the engine was hard to start it will wipe the
oil of the bearing and cause the bearing to grap the crankshaft and hurt it on start up. The bearing then gets
oil and it runs for a little while and you notice it more when the oil gets hot and thins out.
The number 3 and 7 rods are the last one to get oil because they share the number 4 mains journal and they are the last pair that share a journal and split the oil to that journal. The number 5 main just feeds one rod and can get 3/4 the oil that number 4 mains gets and the rods gets more oil because it is not sharing it.
I feel that this happened on start up and maybe this rod journal was bigger or out of round but that should have been caught when put in. These are some of the resons we like to dyno test the engines before they leave because this way we can make sure they are broke in right and that we did our job right. Even with all of this we still have a problem every now and then.
Make sure that the oil galleys in the block are not blocked anywhere. You are reading the oil pressure right out of the pump before the oil really gets to any of the bearings or anything. There could be a restriction and you would not know it by the oil pressure gauge. Building engines can be a ***** for sure. Good luck, Keith Craft
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