Jac Mac you are correct about the oiling and the rods. My mistake on that and I must have had a brain fart. The number 7 is the most common to have the problem and then the heat transfers to the number 3 but he had not heat.
Does sound like a dry
oil start up problem or something possibly blocking one of the
oil galleys. I have gotten a bad bearing and caused this before and could find no reason why it did it.
With the middle three mains feeding two rods each that is normally where you will see a rod bearing problem. Good luck, Keith