I am a Dyna owner but have always wondered why the ST line of bikes use the external oil tank?Is it because of the counterbalaned engine and not enough room in the crankcase?Thanks for the help.

06 Dyna SG

[IMG]local://upfiles/5368/5E7424EE33654DA0B093595DAC5617DE.jpg[/IMG]

 

On the ST the battery is located under the seat, behind the horseshoe shaped oil tank.

...not sure if this helps

 

I think your right, perhaps also to help with suction head on the oil pump maybe? perhaps its system operates at a higher pressure...

 

It is difficult to understand yourquestion. I think you're asking why the oil isn't just dumptedin the bottom of the engine, like your lawanmower. The bikes use a dry sump engine anddry sump engines havean external oil tank because the oil has to be held somewhere. It (the oil, which is what I presume you are asking about) is not held inside the crankcase because of what is called 'windage'. Windage, in a horizontal shaft engine, is the name given for the mist of oil created when the bottoms of connecting rodsand crank journals and counterbalancesdip into standing oil as they spin around when the engine's running. Not only do the moving parts hitting the oil needlessly expend energy that could be put to better use but it also distrubs and more importantly aeriates the oil. The oil turns into a mist inside the engine. The misted oil that gets pumped erodes internal parts more quickly than liquid undisturbed oil, particularly oil pump impellers and the walls of the pump but also bearings to some extent. The actual problem is caused by cavitation as the microscopic bubbles that have been created in the oil burst. A third problem is that aeriated oil doen't transfer heat as well as the liquid does and transfer of heat is one of the main functions of oil in an engine (sealing the rings is its first and most important job, heat tranfer is second, and lubrication is third)/ Anyway the short answer is that dry sump engines have two major advantages over wet sump engines - they capture more useful power and they have ever so slightly improved internal wear characteristics but they have other advantages too, primarily in cooling. Dry sump engines by definition require that the oil be removed from the system, wet sump engines - which are less efficient - hold their oil in the sump.

 

plus it makes them look like the old rigids of the 30s and 40s

 

That is an EXCELLENT answer!

 

As much as I liked Kong's answer I must admit that I really liked the 1st answer from Bone2.....

 

BTW As all Harley'shave dry sump engines 's, they all haveexternal (to the engine) oil tanks, they just look nicer on softails.
Newer Buells get cuteby integrating the oiltank into the rearswing arm.

 

[quote]ORIGINAL: bronk

I am a Dyna owner but have always wondered why the ST line of bikes use the external oil tank?Is it because of the counterbalaned engine and not enough room in the crankcase?Thanks for the help.

06 Dyna SG

Doesn't have anything to do with being a counterbalanced engine. All Softails have had them. They just look cool.

 

I wouldn't want to give up the way my Dyna shakes at idle, but if I ever did for a Softail, it would be because of the way a chromed external oil tank looks.