Which part of the engine?

Methinks that a plain bearing big end would one of the most critical parts so how would one measure that?

Oil breakdown is the key I suppose as any meaningful measurement comes from lubricant temperature.

Hi M.M. Dan Banjock uses one of those infared devices when he runs his in-line dual Fox 35 set up. It is very accurate, he aims it at the head and tweaks needle valves til both heads are the same temp. I watched him do it but for the life of me I can't remember the temp. Sorry if I got a little off the original question, it was more a plug for the infared sensor.  I think it might have been in the mid 300's? That's just a guess.  I'm sure one of the motorheads will have a better answer.

Rich