Oil sumps

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After watching American chopper and looking at some of my friends bikes, why do Harleys and some other bikes have a big oil tank under the seat? Are they two stroke or something? Is that big tank just for makeup oil? I'm lost.
 
Under the seat is the only place an oil tank will fit on some frames. The classic Harley (and its clones) engine is a dry sump ... all the oil not being circulated through the engine is held in the tank. Two stroke ... are you trying to start another flame war here?
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[ August 12, 2003, 11:59 AM: Message edited by: doyall ]
 
quite a few bikes have a dry sump besides harleys. i know that my suzuki drz400 and honda xr 400/600/650 dirt bikes and have dry sump engine with the oil tank in the frame. it allows for a physically smaller engine and greater oil control. unlike most street cars there is very little oil stored in the engine, the oil is pumped into the engine to lubricate then pumped out to the oil tank.
 
Of COURSE not bro!!!! I just got done reading the cryptokid vs. RX thing. Wow. Don't want to get in the middle of that one. This is one topic I have been unknowledged about and would really appreciate your answer. Just exactly, how does that work? Oil gets pumped to the dry sump, then gets sprayed onto the crankshaft or somewhere thereabouts? Apologize if this is stupid, but I've often wondered about that and never took the time to study it yet. I've heard of dry sumps and side oilers, is this the same thing????

[ August 12, 2003, 01:31 PM: Message edited by: Schmoe ]
 
No question is stupid!!! Dry sumps work pretty much how you described it, oil comes from tank, lubes parts, falls to bottom of crankcase where a smaller scavenge pump sucks it out and back to the tank. that's pretty much it.
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in case you are curious, most aircraft engines (recip and jet/turbine) are dry sump. quite a few motorcycles, porche 911 engines, and most high end race cars are all dry sump. dry sump refers to the bottom of the engine where the oil pan would normally be, but instead of storing the oil in the bottom of the engine there is another pump that pumps the oil to the oil tank. then the oil flow from the tank to the pressure oil pump and it pressurizes the oil and the oil gets distrubuted thoughout the engine just like it normally would on a wet sump (normal) engine would. it is the ultimate control over where the oil is at all times. there is no sloshing in corners and no "windage" to whip the oil into a foam.
 
Close Tim,but the scavange pump has a larger capacity,don't want to pump out less than you put in,the sump would load up.My Honda has 1.5 litres in the sump,1.5 litres in the frame.
 
I am looking at an aircraft point-of-view on teh scavenge. You dont want more in the scav than the pressure otherwise you can cavitate the pump causing it not to suck at all. This is why (on A/C) that there is always something left in the mag-plug sump.
 
you must be talking about recip aircraft engines. on the jet/turbines engines i've learned/worked on the scavenge is much larger than the pressure pumps. the air/oil seperator seperates any cavitation foam. the larger scavenge pump also allows the labrinth and carbon seals to to seal.
 
I am talking mainly with the T-56 Turboprop. there is no separator in this engine. If the pumps cavitate, they loose lube and will lock-up and shear the shaft. so there is always some oil/backpressure in the system to prevent this.
 
i learn something new everyday. i work on T-56's but only do 2 level maint so i don't get into oil pump theory on those much. just valve housings and td amps
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the GE f-110 engines i used to work on had the larger scavenge systems.
are you at LAFB?
 
Yes, LRAFB, I worked for a DOD contracter there, then went full time ANG. been doing it for 18 years ( working T-56). 2-level, QEC's Compressor Mods, Props, Phase, and, of course the line. ready to retire!!! lol
 
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