Last edited by ima4nr; 08-03-2009 at 08:22 PM.
The 'bum has a little info here:
Personally, I would go with an oil meant for the purpose. It doesn't have to be BMW (that's what I use, though), but I would think it should be motorcycle fork oil. The forks won't know if it was meant for a Honda!
Kurt -- Forum Liaison ---> Resources and Links Thread <---
'78 R100/7 & '69 R69S & '52 R25/2
mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!
70's Hondas had ATF specified - if you just want a generic.
I am happy with the 7W BelRay I am using
My front forks were stiff and non compliant. Don't know what was previously in forks but obviously old (grayish and thick looking). I have progressive springs and the 5w worked perfectly for me. The ride is soft but without the dive and mushy handling you get from the stock springs.
74 R90/6 (also know by bride as the Black Hole). 09 R1200 GS. My wife, 1953 model who has survived aplastic anemia and a bone marrow transplant.
I've used ATF in BMWs without any hassle at all. Unknown weight, however. Its thin, I know that and probably like 5w as a guess. ATF is a very clean oil, as it must have some agents for this purpose, but does no harm to my old Airheads. Randy
Paul Glaves - "Big Bend", Texas U.S.A
"The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
ATF Flows around 55 seconds SUS @ 210 degrees, that is right in the middle of the SAE20 wt range. ATF uses a high VI [viscosity index] base oil, that means it is not effected as much by heat and cold. I would think it would produce alittle too much compression dampening in BMW forks. In Japanese damper rod forks it works well. BMW used to recomend Aero Shell no.4 aircraft hydraulic fluid, it was in the SAE 5 wt range, also a very high VI product.
I think as Paul has recomended something in the 5 to 10 wt range is the stuff to use. I have used 10 wt fork oil in a /6 for years and it has worked fine for me.
It is difficult to generalize weights of different brand fork oils as the system in industry use for motor oils supposedly does not work well for light oils for hydraulic fork use. Some fork oil brands at 5 wt act "thicker" than some other brands 7.5 or 10 wt. Found at this site are some readily available brands listed using more relevant numbers:
I recently found that site when researching fork tuning for my Honda. 18 months ago I went through my R100 forks and used Bel Ray 10wt at reassembly. Sharp edged bumps are rather harsh to me given the otherwise soft springing and damping this fork exhibits. Next time I'll try Bel Ray 5wt or something close in cST.