What weight of fork oil to use?

[Armaguidon13]

7.5 are OK on my 77RS and my 90S

[SteveD]

7.5 are OK on my 77RS and my 90S

and on my R100RS 11/1981

[Armaguidon13]

On my 77RS all factory parts
my 90S : sport BMW springs for 90S I've to try 5W
On my 80 G/S progressive springs, they recomand 7.5
My BMW factory manual recomand a Castrol aero oil equivalent to 5W. BMW had never been clear about oil weight but it seems to be clear that more than 10W is for track.

[daz]

Fork allignment Duane? I'm still waiting for Future to get his grout in so he has time to remove his forks! (Get his nuts off). I certainly don't mean fork allignment is not as critical on monolevers. But I don't think it's as big as issure on the newer bikes. Am I wrong? Since I have trouble removing my top nuts I just drop the botttom part of the forks to do seals, etc. (twice in 50 K miles). Doing it that way you only have to worry about the legs being parallel. And you can really get the gunk all cleaned out. But getting back to the original comment, are the older bikes more prone to fork mis-allignment problems?

[Duane Ausherman]

daz, you raise a very good point. Since I have no experience with the later bikes, I have no idea.

However, I can't imagine that stiction is tolerable on any motorcycle. In the early days many bikes had so little fork travel that it mattered little. Basically, most forks were just plain old junk. BMw forks (same as on the Maico) were far superior with the longest travel of any road bike. As forks become more rigid and have longer travel, they need to be in better and better alignment, or you get stiction.

On the first BMWs since the /3 with telescopic forks, the manufacturer didn't do a very good job of quality control. The result was stiction. This factor resulted in injury and death for too many riders. They got a bad reputation and deserved it. BMW didn't have a clue of how to fix it.

This is just basic info and may not apply to modern bikes, but I can't imagine how, or why. Someone splain it to me.

[vanzen]

How is your fork alignment? That is a must no matter what oil you use...

Time and time again, I have seen mc owners use "a heavy" oil to compensate for OTHER faults of the system.
The "heavy oil" may mask these deficiencies. It will never "solve" the problem !
Alignment is critical !
As will be properly tuned damping characteristics, spring rate, and pre-load !
My strategy would be to get these things "just right", and then use the lightest oil possible.
Slowing the system with a higher viscosity is usually not a positive change ...

As far as 10wt being "race only" – ?? – Give me a tuned system and 5wt any day !

[Scoots]

So, as I understand this, as I can't find anything in the manuals and this is my first fork oil change, I should use the 7.5w fork oil, ignoring the listed 10w fork oil in the ReaolOEM.com website - which is fine with me.

The monolever is being "lightly" serviced by me this winter. I have lots of time on my hands, due to the fused vertebraes in my neck, resulting from the 30mph encounter with black ice and my now deceased Toyota 4Runner - not my airhead.

The airhead runs very sweetly and I could steer it with my knees and finget tip pressure - to chicken to ride "no hands" like I did my bicycle. There is no problem with the suspension. Just prior to my accident I had inquired about replacing the Fox Twin Clicker on it - that project has been moved to this coming Spring. I'll be changing all fluids on the airhead, lubricating cable ends, cleaning electrical connections - the "light weight" stuff, as the Dr. has me restricted to lifting no more than my fat head and no driving/work for the next 3 months. Finding the recommended fluids for the monolever was all straight forward EXCEPT when it came to the fork oil. That's why I started this post.

Thanks for your replies

[Major Softie]

Time and time again, I have seen mc owners use "a heavy" oil to compensate for OTHER faults of the system.

Very true. It is VERY common for people to try to compensate for a bike being undersprung by going to thicker oil rather than paying for the correct springs (on all bikes, not a BMW thing). This can be because they are cheap, uninformed, misinformed, or simply because they can't find a vendor with the right spring for their needs, but this is NOT a solution.

"9 out of 10 damping problems are in the springs" needs to be spread as a common truism like the "9 out of 10 carb problems are electrical."

[Frog]

Give me a tuned system and 5wt any day !

I agree completely.

I have experimented with my slash five forks and have settled on using 5wt. I recently tuned a friend's slash five forks and we used 7.5wt. It was too much and not balanced with the rear suspension. I am switching it to 5wt now. You can also experiment with the amount of oil you use. I use less than stock....leaving a bit more air cushion. I weigh about 170lbs.

Once the forks are aligned, I would highly recommend some experimenting. One can really improve the handling of a bike with forks that work well.

BTW, my R100R forks were a little out of alignment.....but not much (.003"). Most slash fives that I have aligned are as bad as .020"

[Duane Ausherman]

Finally, voices of reason arise out of the void.

I know that you wish a simple answer such as the weight of oil alone. To give a close to accurate answer would require knowing a whole lot of other factors. How you ride, your weight, the accessories, alignment, spring condition and the list goes on and one. An experinced rider can take a ride for a few minutes and tell you a lot of what might need to be checked in greater depth. If you know that person, then ask for an appraisal. However, few are qualified, I am not, as I don't know those models.

Working with Frog on these issues allowed me to watch a smart person discover a lot about the forks and how important the alignment is. On my bikes (old) and my weight (175) I prefer 5 wt. That assumes that all else is correct.

REALOEM? What is that? I would follow the factory owners manual first.

Not only do people cover up problems with the wrong oil, they actually cause problems by using the wrong procedure to change the oil.

You are to be complemented by asking here. The factory procedures have been tested for many years by these guys and some are found wanting. If you are able to reject the nonsense answers, then you will find very good advice here.

It sounds like you are quite limited in the range of activity allowed by the boss (Dr.) for some time, but you wish to "do something" in the meantime. Good, standard maintenance is a very good place to start. Take photos. Keep records and log everything you touch and do. Take a lot of digital photos, a lot.

I suggest trusting Frog, major softie, vanzen and a few others. Watch out for that old guy Duane.