Primary OIL, what Weight ?

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Jul 19, 2018 | 06:21 PM

#111

TriGeezer

Seasoned HDF Member

Joined: May 2012

Posts: 32,934

Likes: 36,031

From: Carlsbad, CA

Quote:

Originally Posted by smithbrl

HD Formula+ here.

:Icon_that: My bikes seem happiest with it.

Aug 12, 2018 | 07:06 PM

#112

BlewMoney

Stage II

Joined: Aug 2018

Posts: 2

Likes: 0

From: Stafford, Va.

my clutch has never been smoother than it is with atf, I have a local shop that helps me with stuff I don't think I can do and he has used atf for years, I was a little skeptical at first but I like it

Aug 15, 2018 | 07:14 AM

#113

jjavman

6th Gear

Joined: Jan 2013

Posts: 12

Likes: 1

From: Canada

Quote:

Originally Posted by mfuchs2004

Sure, but we're talking about the primary here. No stress at all, no heat to speak of. Lot's of folks run 'em open. You can put you hand on the primary after sitting in traffic.

Not on mine you can't!

Aug 15, 2018 | 05:33 PM

#114

woodthumb2

Tourer

Joined: Sep 2016

Posts: 372

Likes: 83

From: FL East Coast /Western NC

20w 50w v line 4 stroke dino in all 3 holes... change engine every 2 to 3...

Aug 15, 2018 | 11:23 PM

#115

Joe from So Cal

Tourer

Joined: Mar 2018

Posts: 462

Likes: 87

From: Southern California

Mobil 1 synthetic ATF.

ATF is a waste of money? I blew $22k on a motorcycle that is used strictly for fun.

Aug 16, 2018 | 07:27 AM

#116

ratpick

Road Captain

Joined: Jun 2012

Posts: 574

Likes: 156

From: Big Sky Country

10w40. Pretty sure that was standard before HD syn3 and all these "chaincase/primary" specialty products. I use Amsoil motorcycle synthetic; obviously opinions vary re synthetic or conventional but what I would NOT do is run standard automotive synthetics as I was given to understand they can cause issues with wet clutches while motorcycle synthetics should not. For conventional oil I would run a diesel version for same reason, though would likely be a 15w40 in that case. I would likewise avoid running "gear" oils in primary, 80w90 and such, as they have other additives designed for transmissions/differentials. I've also heard of heavy gear oils causing issues in older chain driven transfer cases on 4wd pickups that specified 10w40 engine oil, and while it seems unlikely to be a problem at temps we ride bikes I don't see the point risking it.

Last edited by ratpick; Aug 16, 2018 at 07:37 AM.

Apr 20, 2025 | 12:43 AM

#117

Baron60

Novice

Joined: Dec 2024

Posts: 23

Likes: 9

From: Melbourne

You may want to think about this too. Although the primary doesn't generate much heat in and of itself that's not the only concern when choosing a fluid.
The primary on your motorcycle is not a seperate entity. It is attached to the engine and it acts as a giant heatsink for that engine. [/QUOTE]

100% correct of the primary acting as a heatsink. After a good ride in hot weather, when I come to a atop I can't even lean my left leg against the derby cover. There's a lot of heat going on in there and that's the reason why I run a 100% PAO Ester 10W-40 JASO rated motorcycle oil in there. Synthetics handle the heat better no matter what weight of oil you're using.

Apr 20, 2025 | 06:58 AM

#118

Rounders

Seasoned HDF Member

Joined: Mar 2021

Posts: 18,245

Likes: 3,679

From: backwoods

Quote:

Originally Posted by Baron60

100% correct of the primary acting as a heatsink. After a good ride in hot weather, when I come to a atop I can't even lean my left leg against the derby cover. There's a lot of heat going on in there and that's the reason why I run a 100% PAO Ester 10W-40 JASO rated motorcycle oil in there. Synthetics handle the heat better no matter what weight of oil you're using.[/QUOTE]
I think that has gotten worse with emissions and bigger engines. My 103HO is not as bad as my 2007. My 95" not as bad, and I don't recall it being that bad when stock 88.

as for fluid, I really don't know if it matters, in any of the holes. For years I ran with syn3 in all 3 holes. Then I tried red line. Then Harley mechanic got me to change to belray. I am not sure big difference. Tried it one of my primaries. Not sure a difference.