First, the observation. I switched my transmission fluid to a synthetic 75-140W. It did a fantastic job all summer, but I was worried about it being too heavy for winter driving. The coldest I've ridden so far this year was 27F, and it was as smooth as it was in the summer. Turned out to be no problem at all.
First question. I've read where some folks are not comfortable with the lighter engine oils. I switched to a 5-50W 'racing' oil, and have had great results. I chose it because of some testing that I seen done on a track, and it seemed to have worked well. Being a 'racing' oil only qualifies it for a more aggressive additive package, yet it still has the same detergent levels as most other oils I've seen. One reason for chosing the 5, was pumpability, or in other words, getting through the eninge as quickly as possilbe at start up. I don't rev the engine at all during the start up, so shouldn't be loading it too heavily. My tempshave dropped, and I've seen a HUGE drop in engine wear (by analysis). So I'm curious why some are against that "5" number, or even the '45' weight difference.
Second question is regarding the primary. I posed this question under the primary oil section above, but got no responce. Seems that the HD clutch material is not all that different, if at all, than clutches used in import bikes. Imports generally use one oil for all purposes (engine, trans, and clutch). These bikes, generally, put out much more power than HD, as well as higher RPM's, yet seem to have no problem with the friction modifiers used in their oils. Why, then, should we be concerned about additives in our primary cases?
Look forward to some opinions, thanks.
Frank

 

Well, a 5 wt oil is pretty thin at that end and usually has friction modifiers. I guess the simple answer would be, it doesn't meet HDs minimum specs for an engine oil (outside the allowable viscosity range). That range would be a 10 wt. at the low end and 60 wt. at the top of the range.

Our engines are set up much looser than the watercooled, modern high revving engines a 5wt oil is primarily recommended in. It just may not afford enough protection under all conditions.

As for the clutch thing, my understanding is that the friction modifiers in some oils make for clutch slippage. Since HD seperates the functions of the three lubes, it makes sense to me to use Type F ATF which is made for wet clutch operation, like HD and older Fords.

remember, Japanese motorcycles that use one oil are lubricated under pressure and have different operating conditions than HDs. Ideally, use a lubricant MOST suited to the task. The one in all three is a compromise. Maybe acceptable but not the most use specific application available.

One oil in all three subjects ALL THREE to contamenants from three differing sources. Why do it if cheap ATF lubes the primary chain and works well with the clutch and gear specific oil is available for the transmission? Is it somehow less convenient to open cans or bottles with different labels? Other than saving a couple of minutes in maintenance, I see NO advantage.

JMO,
EZ

 

The F series BMW factory spacifically says no synthetics due to clutch problems.

 

All modern oils normally used by HD riders, including all the high-quality synthetics, contain friction modifiers, and these are very beneficial. What the 5w50 will have in abundance is viscocity improvers, and IMO this isn't a good thing. These additives can break down prematurely under severe heat and the fewer you have the better. I wouldn't go beyond 15w50 in an HD engine, except perhaps in very cold weather.

As you said, friction modifiers may be ill-advised in engines that share oil with the clutch disks, as some of these may cause clutch slippage. Moly is one that is usually mentioned when this subject is discussed, although moly is a very beneficial additive for the engine, IMO.

 

An air cooled MC engine will literally "cook" the viscosity improvers out of oil so the smaller the number between the base oil (20) and the weight it gets heated to (50) the longer it will last because it has less VI's. This applies to all the group III & group IV oils. Redline is a Group V and has little or no VI's. I won't go below a 20w base oil in a Harley. Note: Once the VI's in the oil begin to break down the by products of this oxidation will actually cause the oil to thicken.