It's no secret that Nissan's RB engine gets a bad wrap for oiling issues. Some consider the OEM oil pump design to be the Achilles Heel of an otherwise fantastic engine. Why is this?
It all starts with the crankshaft. RB oil pumps are driven by a flat section machined into the crankshaft that rotates the oil pumps' drive gear. Sounds pretty simple right? The crankshaft turns and so does the oil pump -- So what's the problem? The problem is that Nissan thought that it only needed about half the area of the crank that actually engages the oil pumps drive gear, otherwise called the "Short Nose Crank". Sustained high RPM, frequent rev limiter bashing and hard shifting can cause this short nose crank to round off or crack the drive gear causing the oil pump to stop producing oil pressure. We all know what happens when oil stops flowing in an engine.
Nissan realized it's shortcoming and in later model RB26 added what is referred to as a "Long Nose Crank" that fully engages the oil pump drive gear. Ok, so what if you aren't a late model GTR guy? Luckily there are plenty of options out there today that can help you bombproof your RB!
A simple and affordable solution is to fit a collar to your crankshaft that extends the surface engaging the oil pump drive gear. This is a major improvement from the OEM drive configuration but it's not entirely bombproof. Nissan also didn't use the best quality materials for their oil pump drive gears, so these can still round/crank/fail even with an extended collar. It's highly recommended to fit billet gears into the pump alongside a crank collar to improve the reliability and longevity of the pump.
Alternatively a few companies have released "spline drive" collars that lock the oil pump to the crankshaft similar to how your transmission input shaft locks to your clutch discs. These collars require special drive gears and usually are ordered in a kit for a specific type of oil pump.
To recap, if you are building an engine or have it apart for maintenance, take the time to make some upgrades to your oil pump/crank. Determine what your plans are for the engine and upgrade accordingly.