Ive "read" that you dont want synthetic oil in primary cuz it is very slippery and may cause preamature clutch slippage.... never tried it myself good ole dino 15-40 works great tho

 

MA2 (L-EMA2) is what u look for in oil to be used in a wet clutch

 

For those bashing synthetic don't knock it unless you have tried it. And trying it in conditions that stress the oil is the best way to compare.

20/50 Royal Purple is what I use however Amsoil (& also Redline) is also excellent stuff & many feel is superior to Mobil 1. The one advantage Mobil 1 has is it's easier to find locally & cheaper at Wally World thus I use Mobil 1 in my cars, $25 for a 5qt jug is hard to beat!

Anyways, the difference between dyno & synthetic is HUGE on a air cooled motorcycle. I have done probably 100-200 parades on various HD's (present HD has only been in 2 parades) & when I use dyno in there the bike pings, throws out massive smoke & just runs horribly in 90+ weather. Swapping the oil to a good sythetic it will still get hot however zero pinging, smoke etc since the oil doesn't get thin when the temps get so high.

Synthetic can go longer then dyno between oil changes but not the 10-15K miles many car manufacturers claim, that's just scary!!!!

Mobil1 is also usually on the thin side of oils, not as thick as a comparable weight oil so depending on the conditions sometimes you need to step up to a higher weigh due to thinning at high temps.

 

The primary chaincase is not as "harsh" of an environment as the motor or tranny and I just don't think there are any real advantages to using synthetic in there. JMO

 

Yep. Could use butter if you wanted. No combustion gases, fuel contamination, or oil pressure worries. Just slick things up.

 

I guess you two rocket scientists missed the title of this thread: Primary oil, what weight?

Primary oil has no stressful lubrication duties. It mostly transfers heat. There is nothing about synthetics that does that better than regular motor oil or even auto trans fluid. That's all that HDs discontinued Primary Fluid was.

So come down off of your synthetic high horses on this subject. Save it for all those interesting Oil threads.

 

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.

 

I'm using ATF in the primary on our 97 RKC and have hade no issues at all with shifting or clutch action. Weight / oil grade has not been any problem.

 

Red Line is the best blood i've ver used. Highly recommend.

 

Amsoil all three holes!!!!! 20/50