Harley-Davidson Primary oil

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Kinda reviving/creating a new thread on Harley-Davidson primary oil. The latest thread dates back last year and , no pun intended, primarily deals with using ATF in the primary. I'm due for a primary change and currently have Rotella 15w40 dino in it. On hand to avoid going to the store, I have lots of M1 15w50, M1 4T 10w40, M1 V-twin 20w50 and Mystik JT8 15w50 syn blend. Looking at M1's website, back in 2007 (!!) they recommended the 4T 10w40 over the V-Twin 20w50. Current bottles of the VT 20w50 show that it's good for all three holes. I called M1 tech support and they were stumped!! The tech stated he was "sure" both would be good, but thought the MFR's viscosity would be best. I said that goes against what M1 has on line. The tech stated he would research/dig around, and get back to me. Oh well ... I'm sure any of what I have would/will be fine, but what are some H-D owners thoughts ?

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I've used Redline, Amsoil and Harley's oil in my primary. Any of the oils you mentioned will most likely work fine but I probably wouldn't use the M1 10w40 simply because it's not a w50 weight, but that's just me. I've been using the Harley Dino in my primary for the last couple of years with no problems. The primary seems to run a little quieter with the Harley Dino. I use Redline in the engine and transmission.
 
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troop

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If I were to do it today, I'd likely go the Mystik JT8 15w50 syn blend route. I kinda question the need for full syn in the primary, and think it would serve a better purpose in the motor of my H-D and shared sump of my 800 Tiger. I have time. Curious to see what M1 might have to say.
 
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You haven't mentioned anything specific about your bike, but that said I'd probably use any of those in the primary except the M1 15w50 only because it's not designed for wet clutch applications. For the rest of the oil you listed I bet you'd be hard pressed to tell a difference among them, even if you're the paranoid type the viscosities are all so similar you're not going very far out on a limb either way. My experience and opinion is a stock Harley primary has a pretty large window as to what works in it. If you really want to stray off the reservation you'd be going to ATF, that's truly different than anything you already have, but I know that's not your question. I don't think you have a loser in the bunch, everything you have is more similar than different for this purpose. But if I had to pick one of those, I'd say 10w40 just because I'd save the other stuff for the engine where I'd much prefer a 50w.
 

troop

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My 2009 FLHT has approx 29k miles on it with original primary guts, other than a new(er) SE comp. Punched out to 103" with some head work, cams and tuned with a Power Vision. Produces 110hp/115tq, nothing crazy. That said, I'm not a big romper on the bike. It has lived a life of "normal" riding with no crazy burn outs/hard shifting. Basically, a lazy primary life. Now, I did remember that I also bought a few quarts of Quicksilver 10w40 full syn m/c oil when it was also on clearance at Walmart for $3/qt. This could be my synthetic alternative.
 
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I use Rotella T 15/40 wt oil in my primary. '05 Road King with 70k on the clock, original primary inards. It holds a qt, so I buy it in 5 qt jugs and use it in mowers also. I find it makes shifting into 1 st gear just a click, no bang like the 20/50 would. For the price you can't beat it. I change it when I do the motor oil. I can't justify spending anymore for something your just going to throw away.,,,
 
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In my 08 Road King (I purchased new and rode for 57,000 trouble free miles 10 years) I used in my Primary anything from HD Syn 3, Mobil1 20W-50 V-Twin and Spectro Heavy Duty Primary Chaincase Oil (85W). My go to was mainly Mobil1 since it was sold at my local Wally world, cheaper than HD Syn3 and closer to home. Changed @ every 5,000mi. oil change. The Spectro gave me a more positive clutch grabbing non-slip performance. Any oil is better than no oil as they say, but still can't bring myself to even thinking of ever using ATF fluid (blended or not) in my Primary case. Currently using Spectro Heavy Duty Primary Chaincase Oil in my 2016 HD Ultra Limited. Very pleased. https://spectro-oils.com/heavy-duty-primary-chaincase-oil/
 

troop

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And the verdict was .... none of the above smile Wife placed in order today thru Amazon, so I tacked on a quart of Redline V-Twin full syn primary oil. My primary takes 36oz, so I'll add 4oz of some left over Shell Ultra 4T 15w50 syn. WTH...
 
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troop

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Order placed/on way .. Next time
 
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I know this is Frankensteining things by reviving a really old thread, but it’s the most recent thing that search pulled up. Has anyone ever used Motul 4100 Power in a Harley Twin Cam (96 ci)? I have 20 liters of it and sold the Subarus I was mixing it in (they only needed API SL). Crankcase, primary, trans? It’s also API CF and ACEA A3/B4.


https://www.quickfds.com/out/19953-39659-26856-014868.pdf
 
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Being Harley doesn't have any API approvals on it's oil, If I needed oil,I would use it. Nothing special oil will work in a Harley. Your oil says it meets the SL api standard, which my Kawasaki says to use along with the jaso ma2 rating for wet clutch performance. In my Harley. I used to run Valvoline 20/50 wt in the engine. Rotella t 15/40 wt in the primary, which I felt helped with smooth clutch operation. And 70/90 wt gear oil in the trans. It shifted smoothly and was quiet. Thru the years you'll see where people have used every wt or brand of oil in their Harley's without issues. The biggest difference in the oil would be, it was designed for a water cooled, cooler running engine. The heat from a Harley engine might cause higher consumption.,,
 
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In my Harley's I run - 15w40 in the primary, 20w50 in the engine and 80w90 in the transmission. No issues and way cheaper than the stealership when bought on WM online.
 
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