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Tuesday, January 25, 2011

Sealed Crank Case

The VFR1200 motor features a "sealed crankcase" and it took me a little while to figure out what that meant. It's a unique and clever setup.

I refer to it as a "semi-dry sump" design. The oil reservoir is still a sump pan at the bottom of the motor, but the crankcase is sealed in a separate chamber above it. This design combines some of the efficiencies of a dry sump design with the practicality of a compact wet sump design. "Windage" losses from a crankshaft whipping the oil around in a wet sump are eliminated by sealing the crank chamber from the pan below it. Honda designed a special 2-rotor oil pump. One rotor acts as a feed pump to force oil up into the crank bearings and top end, while the other acts as a scavenge pump to suck oil out of the crankcase, then jet it on the transmission gears before it drains back into the pan. No bulky, leak-prone external oil lines are neccessary because of the simple gravity drainage design.

Another advantage is better compression ring sealing and reduced blow-by as a result of the slight vaccuum in the crank chamber generated by the scavenge pump. This oiling system cools the engine efficiently as well. High-pressure jets mounted under the cylinders squirt oil up into the undersides of the pistons, helping exchange the heat of combustion. The motor also uses a high-spec continuous oil pressure monitor, which is constantly taking readings and can sense a drop in pressure before the bearings are damaged.... unlike a conventional system which sets an "alarm" when the pressure drops below a fixed level.

All of these small efficiency gains combine for a motor that's more responsive and powerful. This design is similar to the oiling system in my CRF250X off-road racer, and Honda claim that it is used in thie RC212V MotoGP racebikes.

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