Ohlins Rear Shock on F800GS

[The Griz]

Originally Posted by Gumbeaux

Did you guys find any written instructions on how to best remove the rear shock? Or did you just wing it? It does not look too difficult, but I remember there were a couple tips and tricks on my old single F650 that made the job a lot easier.

Any advice appreciated. My BM802 on it's way soon...

A decent how-to comes with the Ohlins BM-802.

It's really pretty easy:

-Remove seat
-Remove plastic upper shock cover, cutting zip ties where necessary
-Remove fasteners that hold the rubber chain guide
-Remove upper bolt
-Remove lower bolt
-Remove shock by pulling it out from behind

-To install Ohlins do the above in reverse.

Use a new bolt in the bottom, and reuse the top bolt. Threads should be clean and dry for the top bolt. Clean the threads in the swingarm mount point and the threads in the upper mount point too. If you must reuse the bottom bolt (not recommended by BMW), reinsert it using the highest strength over-the-counter thread locker you can find. Torque top and bottom bolts to 100Nm.

Easy peesy lomen squeezy.

[Motorfiets]

Originally Posted by The Griz

Use a new bolt in the bottom, and reuse the top bolt. Threads should be clean and dry for the top bolt. Clean the threads in the swingarm mount point and the threads in the upper mount point too. If you must reuse the bottom bolt (not recommended by BMW), reinsert it using the highest strength over-the-counter thread locker you can find. Torque top and bottom bolts to 100Nm.

Easy peesy lomen squeezy.

why does the new bottom bolt?

[The Griz]

Originally Posted by Motorfiets

why does the new bottom bolt?

Because the BMW OEM bottom bolt uses a very high strength microencapsulated dry thread locking agent that comes pre-applied on the bolt. This does two things: 1) holds much stronger than any wet thread locker I've been able to find at a hardware store (red and blue Loctite and Permatex), and 2) since it's dry thread locker, it does not alter torque values. When you use wet thread lockers you have to reduce torque values slightly as the wet thread locker acts as a thread lubricant.





PS, I'm not saying you or anyone has to use a new bottom bolt, I'm simply saying that I do every time (my opinion) and that it is what BMW does when they service the rear shock. It is what it states in the service manual:

[bxr140]

Originally Posted by The Griz

since it's dry thread locker, it does not alter torque values.

At the risk of this being taken the wrong way...

Technically, aerobic (dry) thread lockers require the torque to be increased over a plain fastener to obtain the proper preload, since the stuff is really just thread filler material and thus increases the running torque in the same way that a dirty/rusty bolt is harder to tighten. In this case (which I realize is the basis for Griz's statement), since we can presume BMW specified their torque based on a bolt that has a known amount of dry thread locker already applied, their specified 100Nm is the proper torque wrench setting.

Big picture, I wouldn't necessarily characterize wet as any better or worse than dry, nor any stronger or weaker, depending on the compounds used. Its really more of a case of practical manufacturing...application specific pros and cons, as it were.

In the case of the lower shock bolt, the bosses are cast right in to the swingarm in a way that makes some kind of thread locker the obvious choice, since there's no nut and you don't really want to crank up the bolt preload too much with that configuration and material. In order to ensure the bolt stays torqued BMW wants to make sure the correct amount of thread locker is applied (and more probably, that thread locker is used at all)...and to that end, its most convenient/consistent to have a lock patch pre-applied to the bolt, then tell everyone they need to use a new bolt every time.

Really, its a simple matter of the best solution being the easiest solution, and vice versa.

[The Griz]

Originally Posted by bxr140

At the risk of this being taken the wrong way...

Technically, aerobic (dry) thread lockers require the torque to be increased over a plain fastener to obtain the proper preload, since the stuff is really just thread filler material and thus increases the running torque in the same way that a dirty/rusty bolt is harder to tighten. In this case (which I realize is the basis for Griz's statement), since we can presume BMW specified their torque based on a bolt that has a known amount of dry thread locker already applied, their specified 100Nm is the proper torque wrench setting.

Big picture, I wouldn't necessarily characterize wet as any better or worse than dry, nor any stronger or weaker, depending on the compounds used. Its really more of a case of practical manufacturing...application specific pros and cons, as it were.

In the case of the lower shock bolt, the bosses are cast right in to the swingarm in a way that makes some kind of thread locker the obvious choice, since there's no nut and you don't really want to crank up the bolt preload too much with that configuration and material. In order to ensure the bolt stays torqued BMW wants to make sure the correct amount of thread locker is applied (and more probably, that thread locker is used at all)...and to that end, its most convenient/consistent to have a lock patch pre-applied to the bolt, then tell everyone they need to use a new bolt every time.

Really, its a simple matter of the best solution being the easiest solution, and vice versa.

Not taken the wrong way at all. Good points, bxr. Things do go the other direction too though. Yes, dry thread lockers require more force to achieve proper torque. Agreed, and BMW specifies 100Nm to do so with this dry thread locker on the bolt. However, when a wet thread locker is applied it could possibly, depending on the chemical makeup, act as a thread lubricant, meaning force should be reduced as to not over-torque the bolt. Torque wrenches only read correctly with dry and clean threads. Therefore, caution should be taken when torquing this bottom bolt so that one doesn't 'butter' the aluminum threads in the swingarm.

That said, Henkel (Loctite) claim that their wet thread lockers do not alter torque values:

From Henkel's website, the makers of Loctite products:

http://www.loctite.com.au/cps/rde/xc...0_AUS_HTML.htm

Modern anaerobic thread-lockers such as Loctite 222, 243, 262 play a major role in improving the reliability of bolted assemblies, not simply by preventing premature loss of clamp load but more importantly, by controlling the friction characteristics of the metal surfaces of the fasteners. Even apparently identical fasteners from the same batch of steel, and having undergone the same heat treatment, can exhibit considerable difference in clamp loads, even when torqued to exactly the same levels. The explanation lies in variations in the “K” factor for the fastener. A simplified model for the relationship between the torque applied, the fastener diameter, the force achieved or required, and the “K” factor is:
T = KDF, where
T = Torque – Nm (inch-pounds)
D = Nominal diameter of fastener – m (inch)
F = Clamp Load – N (pounds)
K = “K” factor. An empirical constant which takes into account friction and the variable diameter under the head and threads where friction is acting (it is not the coefficient of friction, although it is related to it).
Values of “K” can be determined experimentally, see Table 2. The range of values for any lot of fasteners tested was plus or minus 14%, however different fasteners lots increased the variation to plus or minus 20%. The variation in friction (and therefore “K”) is wide since it is the result of extremely high pressures acting on surfaces which vary in roughness, oxide levels, plating finish and thickness, and lubrication types and levels.
Note: These values were obtained using 16 TPI, 3/8 UNC nuts and bolts, where the bolt was captive and the nut was turned. Both the threads and the nut face were lubricated. An unlubricated thrust face, either nut or bolt head, can almost double the “K” value.
The dry solvent cleaned bolt would never achieve the clamp load for which it was designed, irrespective of the amount of torque applied, while the bolt lubricated with anti-seize compound (which is not an uncommon practice with the mining industry and heavy engineering) is stretched well into its elastic limit and is a disaster waiting to happen. The application of the modern anaerobic thread-locking compound Loctite 243 substantially reduces the torque tension scatter envelope over identical “”as received” lightly oiled fasteners.
The “K” factor variation ranging from 0.11 to 0.17 found in seemingly identical fasteners here results in a substantial clamp load variation. At exactly the same torque level of 24 foot pounds, variations between 4500 pounds and 6700 pounds are experienced. This is not exactly a recipe for reliable engineering assembly. The same fasteners treated with Loctite 243 would exhibit a variation between 4700 pounds and 5400 pounds, which is close to the design clamp load for such a fastener when tightened to 75% of its proof load.





Clearly, Loctite anaerobic thread-lockers perform a task which is more important than maintaining bolt tension, they provide a reliable means of controlling friction forces so that, once again your torque wrench allows you to achieve the correct tension.

[YetiGS]

Threadlocker fight!!! Threadlocker fight!!!








That said, my Ohlins rear shock ought to be here any minute . . .

[YetiGS]

Mine just arrived! I'll install it tonight but won't get to test ride it for a little while.

[dendrophobe]

Originally Posted by YetiGS

Mine just arrived! I'll install it tonight but won't get to test ride it for a little while.

All of you buying shiny toys this winter are making me very jealous...

Of course, I do get to ride mine, even if I do have to literally chisel ice off it every morning!

[YetiGS]

Originally Posted by dendrophobe

All of you buying shiny toys this winter are making me very jealous...

Of course, I do get to ride mine, even if I do have to literally chisel ice off it every morning!

Being here in San Diego, I could test ride it tomorrow. Except my rear wheel is at Woody's. He said I'd have it back by this Friday. **crosses fingers**

[dendrophobe]

Originally Posted by YetiGS

Being here in San Diego, I could test ride it tomorrow. Except my rear wheel is at Woody's. He said I'd have it back by this Friday. **crosses fingers**

Not to derail the thread, but what are you having done? Just an Excel rim and Superlacing, or something even more fun?

[YetiGS]

Originally Posted by dendrophobe

Not to derail the thread, but what are you having done? Just an Excel rim and Superlacing, or something even more fun?

Nothing to thrilling this time. After my third set of bearings started going south I said to hell with it and m having him measure, bore as necesary and replace the bearings. I'm sick of worrying about it.

Oh, and he's putting in a Tubliss system. The beads on the K60 tires are just too damn hard to break out on the trail.

[Ducksbane]

Originally Posted by YetiGS

Oh, and he's putting in a Tubliss system. The beads on the K60 tires are just too damn hard to break out on the trail.

Do tell ...

[Gumbeaux]

Originally Posted by The Griz

A decent how-to comes with the Ohlins BM-802.

Thanks Griz. I wasn't too worried...just trying to get prepared.

[The Griz]

Originally Posted by Gumbeaux

Thanks Griz. I wasn't too worried...just trying to get prepared.

No prob. Glad I could help!

[The Griz]

Originally Posted by YetiGS

Mine just arrived! I'll install it tonight but won't get to test ride it for a little while.

Congrats Yeti! This shock is on a whole new level as compared to stock. It's plush. You'll love it!