K100 Auxiliary Drive Shaft o-ring goes between thrust washer and the drive dog.

85 K100RT While in the process of replacing a slipping clutch at 60k I decided while into the job to pull the bellhousing to replace the oil seal on the back of the drive dog(commonly known as the alternator drive flange).

Had the clutch housing secured and released the hex nut in the drive dog and pulled the drive dog shaft off of the auxiliary drive shaft. Secured by stiction to rear of the drive dog was a o-ring. Up on the the shaft was the oil seal which did need to be replaced.

With my parts replacement list accumulated went to the web and the micro fiche to secure part numbers for all the parts needed for the entire job. I don't like to place multiple parts orders what with the extra costs of shipping. So I try to be completely ready when I order.

I could not locate the o-ring part number on the micro fiche so I called the dealer I usually order my parts through. They were stumped. 25 minutes on the phone and he talked to two of the mechanics in the shop. Also stumped.

I couldn't believe that in 26 years of k bike wrenching and all the forum discussions on seeping oil from alternator area that it was not noticed that an o-ring was to be between the alternator drive flange and the thrust bushing on the auxiliary drive shaft.

I put off my parts order and decided I'd email some more experienced dealers parts contacts. I referenced the Haynes K100 K75 1373 Owners Workshop Manual which lists the part on the Fig 1.8 diagram, has a picture 33.2b, and in 33-6 describes ensuring the o-ring in place before securing the alternator drive flange.

One week no reply. I took my digital micro calipers and measured the auxiliary drive shaft(14.51 mm). I measured the o-ring at 18 mm outside edge. 14.11 mm inner edge. Thickness 1.80 mm.

Anyone know the part number ?

While EVERY shop manual I have (Factory BMW, Clymers, and Haynes) show the o-ring in diagrams and refer to it in the text for both old and newer style one way starter drives, NONE of the several dealer or REALOEM parts fiches show it.

One explanation for its absence would be that it is right at the parting line between what is listed and pictured in:

Section 11 Engine, Diagram #11_4686, STARTER 1-WAY CLUTCH/REDUCT GEAR SHAFT

OR

Section 11 Engine, Diagram #11_4680, INTERMEDIATE HOUSING/ALTERNATOR COVER

OR

Section 12 Engine Electrics, Diagram #12_1631, ALTERNATOR, INDIVIDUAL PARTS


It is possible that whoever was in charge of each diagram thought it was in one of the others, so it got overlooked. Since all those parts are not shown on the same page (like they show in ALL the shop manuals) it would be easy to get left out.

My suggestion is to get the closest standard metric o-ring to what you believe to be the UNCRUSHED original dimension. Take into account which way you believe the intended sealing to be, radially or axially.

Good luck. I'm sure you will find something that will work well.

Thanks Lee. Seriously considered the use of some metric green o-rings left over from air conditioning repair on my Honda Element. The newer materials might hold up better to the environment.

Years ago the local Raleigh BMW dealer Scooterville was going out business and I bought the factory original BMW 1985 parts micro fiche from them. Went to UNC Library in Chapel Hill today as a last resort as they have a microfiche viewer printer area.

The 11-019 section Countershaft listed the o-ring as a 14.0 mm x 1.60 mm.

Part number: 11 26 1 460 459 E

That part number does not show as a current good number.

I bet your fiche showed everything on one page just like the drawing in the Haynes (and BMW and Clymers) shop manuals, not like the current fiches. I bet the o-ring got lost in the redrawing in later years.

At least you have the dimensions.

BMW stopped installing this o-ring years ago.

BMW stopped building these bikes years ago!




What was the original purpose and why was it determined it wasn't needed? It's shown with both the old and new style one way clutches in all the shop manuals and specified to install it.

The engine development engineering diagram calls for an o-ring as the first line of defense against oil migration directly up the drive dog flange shaft. It by design protects the oil seal on the flange shaft from being overwhelmed at the shaft oil seal union. The oil seal at the rear of the of the drive flange shaft is a metal on metal union and does not ultimately stop the oil migration from exiting up the flange head out onto the flywheel. The oil seal is held against bell housing wall and is the final means of stopping oil migration out of the engine.

I cannot find or have I ever heard of an EC(engineering change) to not include the o-ring in the assembly of the bell housing and drive flange. To the contrary the BMW, Hayes, and other technical articles call for the o-ring to be replaced when servicing.

The original I've taken out is in need of replacement. It is flattened out after 26 years of service and creased with the impression of the drive dog flange. What with the measurements available I'll try to find out more about the heat rating to procure a replacement.

Thanks everyone for the discussion.