Nissan 370Z Forum - View Single Post

semtex · 03-26-2010, 11:36 AM

Oops. I missed a couple of additional paragraphs.

Quote:

Sometime in the last few years, in an effort to be greener, Nissan discontinued the use of lead in all engine bearings. We know of this through discussions of sources deep within Nissan which will have to remain unnamed. At this time the engineers at Nissan noticed that warranty claims for bearing failure in the RB26 GT-R engine, another Nissan engine noted for running high oil temps, spiked. Nissan launched an intensive study on the reasons of this bearing failure and discovered that the new environmentally friendly bearings started to loose their load bearing capacity at temperatures as low as 260 degrees. Although there was plenty of reserve strength for normal passenger cars, the turbo high output RB motor pushed many sets of bearings to the failure point. Although you think of lead as a very soft metal with a low melting point, it was still a major contributor to the bearings mechanical properties and resistance to heat.

So as the oil temperatures climb, the bearings soften and loose their load bearing capacity, if the temperature climbs past 300 degrees and the engine is being pushed hard the bearing material can start to flake and spall. This disrupts the hydrodynamic film allowing metal to metal contact, resulting in catastrophic failure of the bearings, the crank, rods and even the entire engine often within seconds. Oil also begins to deteriorate quickly at temperatures above 260 degrees. It starts to oxidize and thicken, loosing its lubricity while forming sludge and varnish. This further compounds the problem, generating more drag and heat in the bearing/crank interface area.