Fork seal change procedure - BMW Luxury Touring Community
 
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post #1 of 7 Old Apr 8th, 2020, 8:04 am Thread Starter
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Fork seal change procedure

After removing the stanchion and replacing the fork seal is there a procedure for venting the air out?

Or do we just slide the stanchion back in and compress it down?
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post #2 of 7 Old Apr 8th, 2020, 10:18 am
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Re: Fork seal change procedure

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Originally Posted by Boxflyer View Post
I had a weeping RH fork seal 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 third 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 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.



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.



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.

2016 R1200RT
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post #3 of 7 Old Apr 8th, 2020, 11:17 am
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Re: Fork seal change procedure

The part numbers are different for sure, but the procedure is the same.

Just remove the bleed screw at the top when inserting the stanchion tube into the slider tube, make the connection at the proper installed extension, then install the bleed screw.

Now you have correct normalized internal pressure, not over-pressurized if you just slide it together and trap the internal air, or not trying to draw the stanchion in if you put the screw in place if the tubes are compressed. Screw goes in after correct installation position is established.

2016 R1200RT
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post #4 of 7 Old Apr 8th, 2020, 11:36 am Thread Starter
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Just to clarify I remove this small screw to release the pressure I've trapped forcing the stanchion down?
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post #5 of 7 Old Apr 8th, 2020, 11:38 am
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Re: Fork seal change procedure

Exactly, when all the parts are in the mounted position.

2016 R1200RT
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post #6 of 7 Old Apr 8th, 2020, 11:56 am Thread Starter
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Quote:
Originally Posted by Boxflyer View Post
Exactly, when all the parts are in the mounted position.
Thank you so much, I really appreciate your help. Apologies for my ineptitude lol

I assume the increased air pressure will eventually force oil past the new seal
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post #7 of 7 Old Apr 8th, 2020, 12:29 pm
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Re: Fork seal change procedure

I don't think that's a problem.
Since the level of the oil is below the seal, there is always an air portion that the wiping action of the seal is dealing with. It's different with USD (upside down) forks, but they seem to work pretty well that way...I'm no expert, I just know how to do the forks the BMW Telelever front end.

Hope this helps.

2016 R1200RT
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