Fork Oil/Seals

[strataj]

My right fork seal is leaking oil.  I'll need to replace the fork oil along with the seal.  BMW calls for Type 1 fork oil.  Does anyone know what Type 1 means?  Is it the weight of the oil and if so what would that be?  I had a seal fail on my 02R1150RT at that time BMW sold fork oil by weight, I used 7.5 if memory is correct. 

[Boxflyer]

7.5 or 10 weight are both going to work OK…since it's just lubricant, not a fluid that needs to function as a critical viscosity for meetering.

 

I had a weeping RH fork seal on my 2016RT from the middle of last summer and changed it out this winter. (67k to date)

The OEM part number is 31428532723 and is a set of parts for 2 fork tubes.

The service manual is nice and clear as to the process and it only took about 2hrs from start to finish with the bike up on my lift.

A tiny quantity of oil can look like a pretty large leak, it's deceiving how much dirt just a small amount can attract.

     

   

I tried cleaning up the original seal to find a cut or some crud on the lips of the seal, but didn't see anything unusual.

I used a universal seal puller to carefully remove the old seal. I'd recommend placing some kind of pad or protection against the edge of the fork to prevent leaving any marks or nicks in the metal.

The next picture shows the black coated surface that takes all the force on the top end of the fork tube before replacing the seals. There is a similar thrust surface in the lower end of the fork as well, but I didn't replace anything other than the top seal and wiper.

  

   

 

  

 

Next I poured out the fork oil into a graduated cup and it was about 500ml. The manual calls for 545ml as well as measuring it during reassembly to be 90 +/-2mm from the top of the lower fork tube. The original fork oil was not contaminated/dirty, so I topped up the volume to 545ml in my pitcher and poured it in the lower tube. With this new volume, it measured from the upper lip of the tube about 75mm, so I kept pouring it out until the measurement was at 90mm...which just about equaled the 45ml I added in the first place...so almost no measurable loss of fork oil. A couple of drops of oil can look like a mess over time.

The oil in the lower slider leg is not going thru any orifices or shim stacks, so the weight of the oil is not very important…it's just there to lubricate the stanchions on the sliding guide elements in the leg…so 10W fork oil is fine…use 7.5W if that's all you have.

 

I used the Motion Pro 08-0551 bearing driver to drive the lower seal squarely to the spacer ring in the lower fork. It only took about 4 light hits with a hammer to drive it home. The new OEM seal comes pre lubed and the wiper seal just presses into the top of the lower fork tube.

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Sliding the upper shiny tube into the new seals is simple and needs no tools or special procedure with the vent screw still out. When the upper fork slider is up in the top fork bracket next to the handle bar, you install a new top nut holding the slider to a torque of 40Nm, then you replace the vent screw with a new O ring.

 

Since I only was working on the RH fork, the LH fork tube is the alignment reference with the Quick Release Axle shaft between the 2 for setting the position in the lower clamp.

 

It instructions were VERY specific about torquing the 2 main pinch bolts in alternating fashion 3 times each to 19Nm.

 

There was never any degraded performance with the annoying small oil leak on this fork tube, but I was tired of seeing some oil and not knowing if it was a drop or a more serious leak.

 

This was a couple of hours well spent, I'd had enough of wiping down the fork at the end of each day of riding to see if it was getting worse...because I knew it was not going to get better on it's own.

[lkraus]

Google "fork seal cleaner". Many times the leak is caused by a bit of trapped dirt which can be removed without removing the forks.  There are commercial tools available, but you can make one from thin plastic, like a water bottle or photo film (old negative). 

[Boxflyer]

Hi Larry,

I tried both my DIY as well as the "store bought" versions of my seal cleaners for this fork I described above.  

Neither one worked.

The DIY seal cleaner is almost the same thickness as the Seal Mate version at .36mm.

 

I have also used the DIY seal cleaner to clean out debris from weeping Final Drive "small" bearings…the one under the little black plastic ring several times.

[dirtrider]

45 minutes ago, lkraus said:

Google "fork seal cleaner". Many times the leak is caused by a bit of trapped dirt which can be removed without removing the forks.  There are commercial tools available, but you can make one from thin plastic, like a water bottle or photo film (old negative). 

Morning Larry

 

Not many times but "most times" the leak is caused by a bit of trapped dirt or washing soap scum trapped between the seal lips & the fork tube.

 

That is about all I do anymore is just clean the darn seal to fork interface then drip in a a couple drops of power steering seal conditioner (stop leak) to slightly soften & condition the seal lips. 

 

Just pry the upper dirt excluder seal up (careful to not damage the dirt excluder seal & fork tube top)  then slide it up the tube out of the way.

 

As Larry mentioned an old 35mm film negative works good as well as about any very thin but stiff plastic. I haven't had much luck with actual marketed seal cleaners as the BMW seal to fork tube fit is very tight.

 

The above works pretty good (almost every time) but it depends on the amount of oil that has leaked out so should be done very early (right after the leakage is first noted), but a little fork oil leakage usually looks like a LOT more than it really is. 

 

The other thing to keep in mind is: if the seal is leaking oil out it then is definitely leaking air into the fork so with the motorcycle parked on the center stand.  That air intake allows the fork oil chamber to gain air volume. Then when the motorcycle is placed on the ground (or ridden) the fork oil chamber goes to positive pressure so that can also increase oil leakage.

 

So I usually do all the preliminary  seal cleaning work on the center stand, then put the motorcycle on the ground to actually clean the seal to fork tube & try to bleed the air pressure out while cleaning. 

[strataj]

Thank you Boxflyer for the detailed write up.  I've got a question about the seal puller, the repair manual uses an expandable puller with a sliding hammer.  From the looks of your photo you removed the seal with leverage from the top, I hope that will work for me too since I currently don't own a set of internal expandable pullers.  Does your puller have a adjustment of some kind allowing the tool to go deeper to hook under the seal?

 

Again thanks for your great contribution to the forum!

[Boxflyer]

My puller shown only has 2 ends that are hooked…one a little smaller than the other.

It reaches under the seal far enough to hook securely to pull out one side.  Be sure to put some padding/protection on the pivot point of the tool so it does not leave a mark on the fork rim.

There are auto parts stores that have "loaner tools" and they often have the slide hammer, you just need to add the hook adapter.

[old_farmer]

I recently developed a leaker on my 2017 with 20K miles. I would like to try the 35mm film trick before moving to something more invasive. How does one remove the dust seal without removing the leg from the bike (at which point I might as well just replace)? I worked at it gently with a screwdriver (couldn't get much of a bite on it due to lack of room) but it showed no signs of budging.

[dirtrider]

1 hour ago, old_farmer said:

I recently developed a leaker on my 2017 with 20K miles. I would like to try the 35mm film trick before moving to something more invasive. How does one remove the dust seal without removing the leg from the bike (at which point I might as well just replace)? I worked at it gently with a screwdriver (couldn't get much of a bite on it due to lack of room) but it showed no signs of budging.

Afternoon old_farmer

 

That is about all you can do is to try to gently pry/work the dust seal out, then slide it up the tube. 

 

If that isn't possible then try letting the air pressure out of the fork, then work some power steering leak stop (seal conditioner) in through the dust seal lips. That will usually help soften the seal & help it to seal better. That can also help to clean the seal sealing lips.

 

You might also try turning the upper tube about 1/2 turn so the seal rides on the tube in a different place.  

[Boxflyer]

Hello old_farmer

I just went out to my own fork to see if I could get the wiper seal up out of the way so I could use the plastic scraper to clean between the lower seal and the stanchion.

First I tried a very small and narrow screwdriver and it didn't get enough leverage when I twisted it...then I tried a stubby screwdriver and it worked right away...so for me a little wider blade had the rotational leverage to get the top wiper out of the lower fork leg.

Here are some pics of this.

Hope it helps.

[old_farmer]

I actually have one of those stub screwdrivers that I use (rarely) for tractor work. I'll give that a try. Thanks dirtrider and Boxflyer for the advice.