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Q45tech »
https://forums.nicoclub.com/q45tech-u112.html
Sat Aug 02, 2008 7:53 am
Why old lead F-770 bearings in Q are to like: Old vs new technology
"VQs and previous generations of Nissan motors, stretching from the QR to the RB series, all use a modern-style bearing material that's fairly intolerant to heat. While older engines used a tri-metal, lead-based alloy (designated F-770 internally by Nissan) that held up well at elevated temperatures, newer bearings use a lead-free material (for environmental reasons) that's far less tolerant of high oil temperatures. This is why most new Nissans from Sentras to Skylines all use oil coolers and bearing failure is so common for track-bound GT-Rs and 350Zs.
At temperatures below 300 degrees F, where most synthetic oils are still stable, the newer lead-free bearing material has already changed chemically and been damaged permanently. Even at 250 degrees F, these bearings have lost significant load-bearing capacity."............................................................
Early generations of the VQ also used small bearings, which have less surface area to reduce friction and mass. The drawback is more load per bearing area. When coupled with a bearing material intolerant of high temperatures, that results in a lot of spun bearings in hard-driven cars. This is why we're seeing larger and larger bearing surfaces on updated versions of Nissan engines, as well as oil temperature sensors wired into the ECU. Add the fact that most new engines feature piston oil squirters, which transfer more heat from the pistons into the oil, and there's a snowball effect of hotter oil, bearing material transfer, increased oil clearances and reduced oil pressure.
Over-revving the stock VQ is also an issue. Newer engines use light pistons with small ring lands and low ring tension to decrease friction and reciprocating mass, and to clean up emissions. Under stock conditions, this shouldn't be a problem, but throw in boost, rich fuel mixtures and raised rev limits, and there's the potential for accelerated cylinder wear and eventual blow-by. The stock rev limiter was designed specifically so that piston speeds do not exceed 4100ft/second, based on the stock bore and stroke. Missed shifts or raised rev limiters could push the stock, low-tension, thin-strip rings beyond the margin of safety and either gouge the cylinder liner wall or cause ring flutter.
We saw the end result of both these issues in our VQ. The engine consumed and degraded oil at an excessive rate and it was the lack of proper lubrication that ultimately led to main and rod bearing failure. But, much to Nissan's credit, the engine steamed along like this for a good 30,000 miles. As long as we kept adding oil, the bearings kept going, although the blow-by and power loss kept getting worse.
Much of the burnt oil could be seen exiting the exhaust under boost or while the car was cold, so we had a suspicion that the stock rings and bore had taken a beating from being driven hard before reaching proper temperatures."
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