Three Different Compartments
Three Different Compartments
I have tried to ask this to several people and keep getting the "its a Harley" answer. So the question is why does harley use three different fluids for oil, tranny, and primary? I came from the metric world and everything is took care of by the engine oil. What is the benefit of the one verses the other?
Cruiser
Joined: Nov 2005
Posts: 179
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I'll give you my theory. Harley makes 3 different models based on different frames, the Dyna, Softtail and Touring. Because of the different frames, about the only component they have in common is the motor, the primary and tranny's are different on all three. It would not be practical to build a separate motor/primary/tranny that would share the same fluids for each of the three different modles.
Extreme HDF Member
Joined: Dec 2006
Posts: 10,045
Likes: 36
From: ST. Louis
My question is, why not have a "Counterbalanced motor" with a "rubber engine mounts"?
I know this doesn't answer you question, but then I didn't stay in a Holiday Inn Express last night either. LOL
Cruiser
Joined: Dec 2006
Posts: 164
Likes: 1
From: milltown, nj
Yea I agree with the practical theory... Also, sharing oil is not always a good thing. My dirt bike is "street legal" and the tranny shares the engine oil... Its not the best because the tranny really hammers the oil and its shot after 500 - 1000 miles.
On a cruiser having the ability to put 20w50 in the motor, 75W140 in the tranny and whatever else in the primary is best since not too many people leave their HD stock with the 88 or now with the 96 motors....
On a cruiser having the ability to put 20w50 in the motor, 75W140 in the tranny and whatever else in the primary is best since not too many people leave their HD stock with the 88 or now with the 96 motors....
Extreme HDF Member
Joined: Sep 2005
Posts: 11,615
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From: Baton Rouge, LA
I think its because (1) its not necessary to control vibration, (2) it adds cost to the manufacture of Dynas and FLH's, and (3) it robs the engine of a small amount of power. About the only improvement would be shake at idle, which would largely disappear with a "B" engine with rubber mounts. Some like me think a Harley should rumble and shake a bit at idle, it being a part of the bike's character.
I think its because (1) its not necessary to control vibration, (2) it adds cost to the manufacture of Dynas and FLH's, and (3) it robs the engine of a small amount of power. About the only improvement would be shake at idle, which would largely disappear with a "B" engine with rubber mounts. Some like me think a Harley should rumble and shake a bit at idle, it being a part of the bike's character.
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Extreme HDF Member
Joined: Sep 2005
Posts: 11,615
Likes: 50
From: Baton Rouge, LA
That said, it seems like Harley is trying to nullify this advantage by recommending one or two fluids for the three holes. At one time, perhaps even now, HD has recommended Syn3 for all three holes, but I've heard (unsubstantiated) they are no longer doing that. IMO, Syn3 is a good oil for the engine, inadequate for the tranny, and overkill for the primary. Factory fill includes HD360 and Formula+ for the tranny and primary, and the same issues apply with this combo. I get the impression the Moco is trying to simplify the oil-change ritual by recommending fewer types of fluids, but I still maintain that this is a convenience factor and isn't best for the bike.
Second, primary oil will become contaminated with microscopic particles from the clutch plates, etc., as can be seen on the magnetic plug when the oil is changed. The particles from the fiber disks won't, of course, but they are present in the primary oil as well. Having this material floating around the engine is not a good thing, IMO, and it's best separating these two. If the engine and tranny had the same fluid I don't think it would hurt except that each has its own requirements. The qualities of a good engine oil are different from that for a tranny, IMO.
Last edited by iclick; Jul 6, 2009 at 11:14 AM.
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Cruiser
Joined: Nov 2005
Posts: 179
Likes: 0
Yes the B motor is a different motor on the "inside" but I believe all three motors share the same case/jugs/heads and are pretty much interchangeable in that aspect. You can't look at a motor standing alone and tell whether it's for a dyna, touring or softtail. But you can look at a tranny or primary and tell which bike it goes on.