Why Harley still uses the 3 hole configuration? It's been done for so long, I'd bet they don't know the reason. What it does do is give you the option of using different lubes for your application. While they sell oil that says it can be used in all 3 holes, most see this as a compromise. Not all bikes are used in the same climates, so being able to tailor the trans and primary lubes makes sense. I like gear oil in the trans,because it's a transmission. The lube requirement is for the gears. There is no acids or gases, or dirt formed when being used. That's why it comes out as clean as it does going in. The primary's oil is to lube the chain and clutch, you can use different wt oil in here if you want,only clutch dust will be found in the oil. Doesn't hurt any thing. The motors oil requires more additives for wear and cleaning. Plus it's the only oil on the bike that gets filtered. I hate to think of what the clutch material that's given off from normal wear, would do in small passageways of like the piston oilers.,,

 

Now that is some funny ****!!!

 

It doesn't do anything to the engine because it gets filtered out. The oil change interval for shared sump bikes is about the same 5-6000 miles. The benefit being easier to liquid cool a shared sump engine plus fewer gaskets & seals between cases that cause oil leak issues. Guys always talk about how much less maintenance there is with an air cooled engine when in fact there are more seals & gaskets in a 3 sump air cooled engine than a shared sump.

I would venture to say that the Sportster engine is the one with the least amount of sealing issues. and the best combination of air cooled shared primary & trans sump but the engine having it's own. Now if they would only make a 1800cc 6speed Sportster drivetrain....life would be good.

 

"The oil change interval for shared sump bikes is about the same 5-6000 miles. The benefit being easier to liquid cool a shared sump engine plus fewer gaskets & seals between cases that cause oil leak issues".

"and the best combination of air cooled shared primary & trans sump but the engine having it's own".

I don't think mfgrs worry that much about how many gaskets they use to accomplish a given task .,,

 

Think about this. My Suzuki Boulevard C90 took about 4 quarts when I changed the oil. When the fluid got hot the heat was distributed to “all” the components.

When I changed all my fluids in the Limited it was around 5.7 quarts. First off, I’m dealing with almost two quarts more than the metric, more oil to distribute the heat right? Second, the heat in the trans and primary should be cooler than the engine oil, right? What about metal filings from the different areas mixing together? I would seem to me that the fluids being separate would be better in the long haul. It also allows you to choose different choices of fluids types, weight, etc.

That said, I vote for 3 holes.

 

I think the 3 hole system is better. I have a metric with a shared sump and don't like the idea. I prefer a specific fluid for a specific job. And in a Harley you can use friction modifiers which control heat and add to the life of the motor. Much better in my opinion however I am sure someone will tell me I'm wrong

 

+1 on that

 

The fluid used to cool water cooled bikes, is what is used regulate the temperature of the motor. And air /oil cooled motors tend to do the same thing. The oils temp is regulated due to the big oil cooler attached. As far as Harley's go, all three holes have magnetic drain plugs, but only the motor has a filter. As far as metric bikes go. they have been using single sump motors for a long time and it seems to work fine for them. The shearing of oil's viscosity may be increased due to the oil being run thru the transmission gears. Some may say what Harley does is outdated, but it does give the owner a degree of "tuneability" for which oil he can use in each area.,,

 

The benefit is the wear materials from the primary and transmission don't go through the engine. (Albeit 90 weight gear oil might not work to well in the engine.) LOL!

 

Not sure what your point is here, doesn`t your T bird also have separate transmission lube and differential lube...