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Dry Sump?????

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Hello can someone tell me what a dry sump motor is and what advantages it has. i am new to yamaha so i dont know what this is but i know they use them in cars like the mclaren to lower center of gravity. thanks :banghead:

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Hello can someone tell me what a dry sump motor is and what advantages it has. i am new to yamaha so i dont know what this is but i know they use them in cars like the mclaren to lower center of gravity. thanks :banghead:

You pretty much answered your own question. To save weight and lower the center of gravity.

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Dry sump oiling has several advantages. First, let's look at what it is. Wet sumps, like road cars and most Japanese motorcycles, carry the oil in a reservoir built into the crankcases or bolted onto the bottom of them. They have one oil pump that picks up oil from this sump and circulates it. Once it runs out of the various lube points, it simply drains back by gravity to the sump, where it starts over.

A dry sump carries its oil in a separate reservoir, or tank, located wherever it's convenient. The feed oil pump draws oil from the tank and circulates it the same way as in the wet sump, but when the oil drains to the sump, a second, higher volume return, or scavenging, pump picks it up and returns it to the reservoir. The return pump is a higher volume so that it will "outrun" the feed pump.

The advantages are, to begin with, that the reservoir is not constrained as to size or location by the design of the engine, so it can be located anywhere, and be of any size, and can even be altered later, without modifying the engine. Conversely, the engine does not have to be designed around a certain sized oil reservoir. In a car like the McClarens, that means you don't have to allow any ground clearance for an oil pan. In addition, the tank can be designed to virtually eliminate any possibility of oil feed starvation from sloshing or odd vehicle attitude. Look at a YZF frame and you'll see that the bike has to be nearly upside down before the oil flow would be interrupted. And, having the oil supply located away from the engine itself isolates it from heat while it's "at rest".

Oddly, the CG advantage these systems give an automobile typically works a little bit in reverse on a bike, because the oil supply is almost always at a higher point than if it were in the crankcases. But the other side of that is, like the McClaren, the engine can be set lower in the frame most of the time.

One thing that most people new to dry sumps discover at some point is that the oil migrates into the crankcases when it sits for a few days, This gives rise to a lot of different situations, like panic over where the oil went, overfilled engines because they weren't run up before the oil was checked, stuff like that. But in all, I much prefer a dry sump. They work better, and that's the important thing.

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Excellent response, Gray, but you left out another important benefit. By not having the oil remain in the lower end, drag on the flywheels is reduced since they no longer have to spin through the oil with each revolution. This is particularly important on high revving engines as it reduces windage (oil thrown up into the crankcase) that can interfere with movement of the connecting rod. :banghead:

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wow thanks alot grayracer and radrick. :banghead: gray when you said oil migrates into the crankcases if you leave it for a long time what do you mean? thanks for all the help.

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kxmike,

after about 2 weeks or so (i've not timed in the in 4 year and 10 months of ownership) all of the oil in the frame downtube works it way into the bottom of the motor. on startup, the oil pumps it back up into the downtube.

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I have found my oil sits in the tank for a day before it drains to the bottom.

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Excellent response, Gray, but you left out another important benefit. By not having the oil remain in the lower end, drag on the flywheels is reduced since they no longer have to spin through the oil with each revolution. This is particularly important on high revving engines as it reduces windage (oil thrown up into the crankcase) that can interfere with movement of the connecting rod. :banghead:

Some people with there cars will knife edge there crank so it will not splash in the oil.

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Some people with there cars will knife edge there crank so it will not splash in the oil.

Yeah, we do that on Harley drag bikes because the clearances between the case and crank are so close that the oil can actually create stiction. Radiusing the leading edge of connecting rods is an old trick, as well. :banghead:

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wow thanks alot grayracer and radrick. :banghead: gray when you said oil migrates into the crankcases if you leave it for a long time what do you mean? thanks for all the help.

Gravity will cause the oil to eventually settle into the lower end of the engine. That's why you can only check the oil level dipstick after the bike has been run for a few minutes. The oil has to be pumped back into the reservoir in the frame to get an accurate reading. :applause:

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Gravity will cause the oil to eventually settle into the lower end of the engine. That's why you can only check the oil level dipstick after the bike has been run for a few minutes. The oil has to be pumped back into the reservoir in the frame to get an accurate reading. :applause:

sweet thanks thats why there isnt a sight glass for the oil. what do you think about the 2006 yz250f? you think its going to be a good bike :banghead:

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By not having the oil remain in the lower end, drag on the flywheels is reduced since they no longer have to spin through the oil with each revolution. This is particularly important on high revving engines as it reduces windage (oil thrown up into the crankcase) that can interfere with movement of the connecting rod. :banghead:
True, in part, but well designed wet sumps have measures included to keep the stored oil away from the crank. These will include windage trays, weirs (like dams, sort of), and specially added panels to guide oil out of the way and keep it there. Even then, throw in hard braking, acceleration, cornering, and general bouncing around, and you see the problem. It gets totally out of control if extra oil is added, though. You would think that such extra oil would be thrown aside, but I've seen film of oil on a V8 crank; it coils around it like a rope and slaps against all the stationary parts of the crankcase. That's where the real drag comes from.

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