I would like to know if anyone is using 20/50 oil in both their engine and their primary? If so why or if not why?

 

Because Harley puts in in my bike when they service it.However I use Mobile 1syn 75w90 in the Tranney,20w50 way to thin>I was advised to do this from several HD tech.

 

I run 20/50 in the engine and primary. It's more conveniant to service. I agree with straitshot151 on the tranny. I also use 75/90.

 

75-90 mobil 1. very smooth shifting.

 

Mobil 1 V-Twin 20W50 in the engine and primary....Mobil 1 75w90 in the tranny. Once this was done found lower engine temps, quieter operation, and smoother shifting.

 

Thank you for the relies.

 

when i won the ReKluse autoclutch i had the opportunity to speak with Al the owner about primary oil and its function...he says they have tested them all and a dino 10/40 with no detergents actually helps clutch lock up better than say Amsoil(i love Amsoil too)...he recommends a diesel oil like Rotella...says its not so much a lube as it is a coolant...i use Rotella 15/40

 

I tried to find the previous thread about how gear oil and motor oil compare viscosity wise, but was unsuccessful...

I'm no expert on the subject, nor do I claim to be. However, here is the gist of the previous thread... Someone had posted a link which compared the actual viscosity between motor oils and gear oils. Apparently, they use two different scales to determine viscosity... One for motor oils and another for gear oils. This means comparing motor oil viscosity numbers and gear oil numbers could mislead you. The big thing I took away from the thread was the viscosity of 75W90 gear oil is almost exactly the same as 20W50 motor oil. Although for a caveman rider like myself to look at the grades on the bottles would lead me to think otherwise, you are running about the same viscosity. This is why the MOCO says Syn3 20W50 motor oil is OK in the trans.

Now I'm sure there are smarter guys than me who will argue the point about motor oil will break down quicker than the gear oil under shear stresses in the trans, but one thing also to consider is the temps you are running the engine oil through vs the trans temps. I would say the trans is cooler and breaks the oil down slower.

Now to the question at hand. I run the same Mobil 1 synthetic 20W50 in both my engine and primary. That is what the MOCO says to do and it seems to work well.

Remember, engine oil gets dirty from carbon and combustion, primary oil gets dirty from clutch material worn off during normal operations, and trans oil only gets dirty from any particles which fall into the hole when you check the level! Once I've changed the trans oil several times and have noted the reduction in wear-in fuzz on the mag plug, I leave it in there for 5,000 miles. When I do change the trans oil, the Mobil 1 synthetic 75W90 comes out as clear as the day I put it in there. Engine and primary oils are different because, regardless of being super-duper synthetic, they absorb more and more particles as they are used. The engine oil filter stops most of these particles, but look at the color of new oil vs used oil and it is obvious some carbon is kept suspended.

Does anyone have the viscosity link?

Edmo

 

I is me; and I is the one who posted the viscosity stuff. Here 'tis, again:

We’ve all heard the usual terms about the “weight” of the oils used in our bikes. 20w-50, 75w-90, 10w-40 - all these terms are bandied about with ease for most of us. But what do they really mean?

Without getting totally scientific, the terms represent viscosity measurements. They aren’t “weights”, as we like to call ‘em. Viscosity is defined as: the property of resistance to flow in a fluid …

We say that lower “weights” are thinner, meaning they flow more easily, or have less resistance to flowing. We want both the ability to easily flow during start up, and more resistance to flow at higher temperatures. The multi-grade oils we use give us both these attributes, and help our engines live much longer than in the day of using straight 50w, 60w, and even 70w in an old Pan or Shovel motor. But there are some tradeoffs with the multi-grade oils. They “shear” more easily than straight oils. Shear is when the oil’s actual molecular chains are sliced into pieces. When that happens the viscosity drops, and the oil provides less protection.

That’s just a bit of a basic oil primer. In the past year or so HD, as well as several oil manufacturers, have started recommending the use of their 20w-50 synthetic engine oil in more than just the engine. You can use it in the primary to lube the chain, and in the transmission, where it must operate in a gear-grindin’ environment. So, how can HD say to use 20w-50 stuff where they once called for 75w-90 stuff? Wouldn’t it be too thin to do the job?

Here’s the answer: Viscosity is measured by different scales for engine oil and gear oil. The two systems aren’t directly comparable, number-for-number. Here’s a reasonably accurate comparison between the two systems. Please remember that I said “reasonably accurate”, as there is some overlap.

SAE Engine Oil = SAE Gear Oil

10w thru mid range of 20w = 75w

Mid 20w thru mid 30w = 80w

Mid 30w thru low 40w = 85w

Low 40w thru 50w = 90w

60w up = 140w


Looking at these ranges we notice that 50w engine oil is the same “real” viscosity as 90w gear oil. So it stands to reason that they might be substituted for each other. But remember that there are other factors involved than just viscosity. The ability to withstand shear, and additives designed for a particular end use are also important.

The shear aspect and the additive packages are why some of us don’t think it’s the best idea to use the 20w-50 engine oil in a transmission. There are many reports of tranny damage where the 20w-50 was used. However, there are currently no scientific studies to prove the damage was the result of the use of those oils. You must make the decision as to your own bike.

Personally, I’ll continue to use gear oil in my tranny. There are enough differences in the engine vs. tranny applications that I feel better going that route.