Cracked R1100GS Transmission Case

Discussion in 'GS Boxers' started by MJ Gurunathan, May 26, 2012.

  1. TXjames

    TXjames High Sider

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    They will also fit the M96 that I have with the use of what I think is called the "clean bearing kit" from BMW. It has a 3mm spacer to compensate for the greater depth of the taper bearing.
    #21
  2. MJ Gurunathan

    MJ Gurunathan Adventurer

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    Hi all.


    So I went back down to the dealership and asked them about the technician about what happened with the gearbox. I got pretty much the same answer as I did from the service rep; that the pin seized and as he applied leverage to remove it, the gearbox threads gave way. BUT he did produce a heat gun and tell me that he tried to heat the pin before removing it - which I think might be a bit too convenient, but there is no way that I can prove that he didn't.

    One of the theories that he put forward was that the wrong type of thread locker was used when the pivot pin was put back in place, but I know that is rubbish because I used the same type of red loctite as specified in the manual. What I think happened was that he tried to loosen the pin, found it wouldn't budge, put a bit more force and *crrrack* there went the gearbox. Out came the heat gun and impact wrench and then miraculously the pin gets removed.

    Let's see what I can do to sort this mess out but I can be sure of one thing: I'd rather sacrifice my own time and work on the bike myself, rather than send it in for repairs to the dealership. What a horrid experience.

    Thanks all for the great advice!
    #22
  3. MJ Gurunathan

    MJ Gurunathan Adventurer

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    OK once again thank you all for the great advice.

    Special thanks to all who have volunteered help in one way or another with parts.

    Here's what I've learnt so far, summarised for anyone who cares to read it. Of course, all of the information below has nothing to do with the R1100S transmission, which I know nothing about and in any case will not fit the R11000GS/R/RT.

    Please correct me if I'm wrong, I'd like to try and get this all right so we can build up a reference of sorts.

    1) Ratios:

    The R1100R/RT/RS/GS M94/M97 transmissions all have the same gear ratios. The M93 transmission has different gear ratios from the M94/M97 transmissions.

    Different final drives are used for different R bikes. The ratios are presented below:

    R1100RS 31:11 (2.818)
    R1100RT 32:11 (2.909)
    R1100GS 33:11 (3.0)
    R1100R 33:11 (3.0)
    R850R 37:11 (3.364)
    R850GS 37:11 (3.634)

    2) Interchangeability (complete gearboxes):

    All M94 and M97 gearboxes are interchangeable. M93 is interchangeable with M94/M97 but you'll get different ratios in the gearbox.

    3) Interchangeability (internals):

    M94 internals will fit M97 housings with modifications to input shaft and rear intermediate shaft bearings.

    M97 internals will fit M94 housings with modifications to intermediate shaft bearings. Some M94s had the newer M97-type bearing here.

    M94/97 internals WILL NOT fit an M93 housing.

    4) Interchangeability (housings)

    The M97 housing has thicker walls and a different finish so there will be some mismatch when the front case of an M94 transmission is bolted to the rear case of an M97 transmission. Opinion is that it is possible to mix and match M94/M97 cases.

    There is no such thing as an M96 transmission.

    Please add on as you see fit. I will try to refine this when I have more time.

    Regards;
    MJ.
    #23
  4. AntonLargiader

    AntonLargiader Long timer

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    Only the intermediate shaft bearing*. You just have to use more shims on the input.
    Doesn't exist.

    * EDIT: in some cases. Some M94s had the newer M97-type bearing here.
    #24
  5. fallingoff

    fallingoff Banned

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    #25
  6. TXjames

    TXjames High Sider

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    True, true. Sorry about the confusion. I got my numbers mixed up. It is an M94 case out of a 1996 RT.
    #26
  7. rutard

    rutard Magnanimous Madcap

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    Does this mean that they can't be matched? Or is it just a cosmetic problem?

    Thanks for the transmission synopsis! :clap
    #27
  8. MJ Gurunathan

    MJ Gurunathan Adventurer

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    I am not sure of this. Dimensionally the cases should be the same, but until and unless I have the cases in hand I cannot be certain.

    Logically this should work. You've got the same swingarm, driveshaft, clutch, clutch bell housing, everything is the same... and if you can swap the gearbox as a complete assembly, surely you can swap housings. Personally I think it is best to keep them as a matched set.

    Honestly if I had some money I would buy a used transmission, tear the bloody things apart and do a Lego on them. Haha! See what fits where using what in which way... whoaaaa....
    #28
  9. MJ Gurunathan

    MJ Gurunathan Adventurer

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    Good day all.

    I would like to share my experiences with all of you, so that I can help anyone who faces the same issues that I did. Sorry this update took so long, but my health hasn't been too good. Finally got the job done though!

    Synopsis:

    Motorcycle Model: 1994 R1100GS, M94 transmission.

    1) Whilst removing the RHS pivot pin for the swingarm from the gearbox, excess force was applied to a seized pin. This caused the housing to crack as in this picture (cracked portion is circled below):

    [​IMG]
    DSC03288-1 by MRF3343, on Flickr

    Tips:
    a) Use the correct threadlocker when installing the pin.
    b) Heat the gearbox around the pin prior to removing it. The heat will soften the threadlocker and make it easier to remove the pin.
    c) If the pin seizes, DO NOT FORCE THE PIN! Drill it out and carry out a thread repair using a wirethread insert.
    d) Oversize holes can be repaired using a solid insert. Cracked holes must be welded, the case crack tested and then retapped.

    2) The crack was caused by excess force that was applied to the swingarm pivot pin. The gearbox was stripped down to facilitate repair. Here are some pictures of the internals of the M94 gearbox:

    [​IMG]
    IMG848 by MRF3343, on Flickr

    And again:

    [​IMG]
    IMG861 by MRF3343, on Flickr

    Tip:
    a) Take pictures as you carry out each step in the disassembly process.
    b) Put all parts in plastic bags. Label them with the BMW part number.
    c) Match spacers to shafts, bearings to races. These parts are already bedded in.

    3) After the gearbox was stripped down, it was cleaned in a solvent bath and then plastic-blasted to remove all traces of the original coating. The gearbox cases were then placed in an oven set to 140 deg. C for about an hour. This was done to drive out any oil or solvents that remained in the porous aluminum. Once I was satisfied that the gearbox was clean and oil free, I handed it to the welder to start the welding process. Here are some pictures of the gearbox after cleaning and plastic blasting:

    [​IMG]
    IMG925 by MRF3343, on Flickr

    And another view:

    [​IMG]
    IMG946 by MRF3343, on Flickr

    Tips:
    a) The paint on BMW gearboxes is very tough. To save time when blasting, soak painted parts in paint stripper to loosen the paint. You can then blast the paint off with some ease.
    b) Use kerosene to clean the gearbox, then a solvent degreaser.
    c) Heat parts in an oven to drive out oil and gases from the porous aluminum.
    d) Plastic bead blast the gearbox casings. Plastic blasting is gentle and will not harm the parent metal. Accidentally blasting a bearing seat or gasket surface may damage it if you're using highly abrasive media like alu-oxide.

    4) The gearbox is made of an aluminum alloy. Some form of inert-gas welding must be used when welding aluminum. In my case, I TIG (tungsten inert gas) welded the gearbox. The material was built up in small sections around the cracked area. Once the crack was built up, the threaded hole was built up to repair sections of thread that had chipped off. Buildup was continued until the hole diameter was less than 24mm. This is because the pin has an M27X1.5 thread; a 27.0mm-1.5mm = 25.5mm hole must be bored to allow the thread to be created. Below are pictures of the gearbox during the welding process.

    [​IMG]
    IMG926 by MRF3343, on Flickr

    And again:

    [​IMG]
    IMG927 by MRF3343, on Flickr

    After blending:

    [​IMG]
    IMG944 by MRF3343, on Flickr

    Tips:
    1) Make sure the affected case is clean and free of oil, dirt and grease before welding. It is important to heat the part in an oven to drive out anything that may 'gas out' during the welding process. This can cause weld porosity.
    2) It is a good idea to build up more material than is necessary. You can always machine the part to size later.
    3) If possible, leave a small amount of undamaged thread to act as a hole center reference and as a guide when tapping the hole.
    4) If possible, do not weld completely the flat surface next to the pivot pin hole. You will need a small portion of undamaged material to act as a datum to machine the face flat.

    5) Once welding was complete, I started planning the machining of the affected area. To set the workpiece up correctly, I needed two datums; one to set the gearbox parallel to my machine table, the other to set the gearbox perpendicular to the table. I set the gearbox up on a milling machine as in the picture below:

    [​IMG]
    IMG1177 by MRF3343, on Flickr

    Here again is the setup:

    [​IMG]
    IMG1178 by MRF3343, on Flickr

    And another view:

    [​IMG]
    IMG1181 by MRF3343, on Flickr

    The centre of the hole was conveniently found to be related to the distance between centres of the footpeg mounting holes. A pin of the correct size was held in the machine spindle and the table adjusted so that the pin could slide easily into the footpeg mounting hole. I then used an edge finder to set the workpiece zero. This hole centre was confirmed by running a threaded rod into the pivot hole on the other side of the case and seeing if it would clamp neatly in the chuck of the milling machine. I also confirmed the hole centre distance from the mating face with the angle plate by comparing it with a measurement (previously taken) of the hole centre distance from datum of the pivot pin hole on the LHS of the gearbox.

    I then bored the hole to 25.4mm ID (0.1mm allowance) by pocket milling. You can see the machine in action below:

    [​IMG]
    IMG1183 by MRF3343, on Flickr

    Sadly I had to de-rig the job as I had to start on another project. Not good practice because this meant that I lost the hole centre and would have to setup the job again (clocking the angle plate, finding hole centre etc) in order to accurately tap the hole.

    Tips:
    1) Again, make sure you leave some portion of the original hole undisturbed. This will help you find the hole centre much more easily.
    2) Assemble all your tools before you start. It is best to machine and tap at one go. This will help you save time on workpiece setup later.
    3) Check and recheck dimensions before starting machining to avoid expensive mistakes.

    6) Once I had some free time, I headed down to the shop to start tapping the hole. I used a dial gauge to indicate hole center and then tapped the hole. The picture below shows how the tap was set up:

    [​IMG]
    IMG1216 by MRF3343, on Flickr

    Tips:
    a) Make sure you have your hole center correct. Any misalignment might cause the swingarm to shift or the swingarm bearings to wear and will affect the driveshaft alignment as well.
    b) Tap slowly. Make sure the tap is perpendicular to the workpiece.

    That's it! Job done. I'll powder-coat the cases and then reassemble the gearbox when I have more time. I shall try to get bearing sizes and seal dimensions so that you won't have to go back to BMW to buy bearings and seals. Saves a great deal of money.

    MJ.
    #29
  10. def

    def Ginger th wonder dog

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    I have always admired skilled welders and machinists...they understand how to fix things broken by those of us who are unskilled with tools or use the wrong technique when repairing things made of metal.

    During the restoration of his 1970s vintage Triumph T100, my brother discovered one of the engine mount tabs on the crankcase was broken. A local welder repaired it without drama for a few bucks. To this day, the repaired case is fine.

    Nice work on the transmission case.
    #30
  11. def

    def Ginger th wonder dog

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    Come to think of it, I would send a bill to the BMW dealer who busted it originally. Not that it will be paid but, just to show defiance, your grit and competence in the face of the dealer's incompetence and poorly skilled mechanic.

    On the invoice I would print, To repair and correct damage caused by incompetent dealer technician.

    Of course, include this set of photos.

    Again, nice work.
    #31
  12. MotorradMike

    MotorradMike MIL-TFD-41

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    Brilliant job MJ.
    You hid this little tidbit quite well and I'm sure most of us missed the fact that you had access to all that equipment.

    Question about the pocket milling if you don't mind.
    Why didn't you simply bore the hole in preparation for tapping?
    #32
  13. def

    def Ginger th wonder dog

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    MJ,

    In your last photo, the tap is shown in a typical tap wrench with the quill of the milling machine above the work. Are you hand tapping using the quill as a reference? Also, what tapping fluid did you use during tapping? Was there any difficulty during the tapping process with the original threads being overcut?

    Finally, alloy can be rather buttery or very difficult to machine. Did you ascertain the alloy used in the case before proceeding? What rod was used to provide the alloy fill?

    Thank you. Continued good luck.
    #33
  14. MotorradMike

    MotorradMike MIL-TFD-41

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    Since MJ is off riding his new bike, I'm going to say what I think def.

    He hand tapped that hole using a pin in the chuck to center the tap using the dimple in the top of the tap.
    A little down force is all that is needed to get it started straight.
    Once you get it started straight, it tends to stay that way. I'd be careful almost all the way through on this job.
    I usually chuck the tap and power it in part way, then stop and go manual after that because I don't have a tapping head yet.

    I've tapped a pile of holes this way but never anything that big in that critical an application.
    Although, with all due respect, he had nothing to lose at that point.

    I bet the case would machine like butter, however, I don't know how it would be after he welded it.
    I'd also like to know.
    #34
  15. vagueout

    vagueout Long timer

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    Fantastic job.:thumb
    #35
  16. def

    def Ginger th wonder dog

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    As a prototype machinst (~1970), I used to tap holes from 2-56 up to 1 inch in alloy and steel plate using a Bridgeport Vertical Mill (manual, no NC). I too chucked the tap and allowed the mill to center and rotate the tap but allowed the threads to feed the tap. My thinking was once the tap was started, it was best to keep constant pressure on the tap to preclude breaking the tap (which I did on several occasions).

    Also, this hands off approach allowed me to apply cutting fluid and compressed air as the tap cut threads. Those were fun days when I learned a lot about metallurgy and just how tough some metals were and were not.

    Alloys were always challenging for me. Most of my work was in alloy. Steel was more predictable to cut. I've never tried much welding. I had a friend who could weld steel and alloy beer cans together without blowing holes in the work...very steady hands and lots of patience.
    #36
  17. MotorradMike

    MotorradMike MIL-TFD-41

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    2-56 in steel 1" deep?
    Hat off to you, I don't even try 2-56 in anything but Delrin, and never more than .250 deep.
    #37
  18. MJ Gurunathan

    MJ Gurunathan Adventurer

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    Hi Mike.

    Thanks very much, I took this as a learning experience. It was fun and I learned a lot.

    I didn't have a reamer that large! I had a couple of endmills lying around so I chose to pocket mill instead. The machine I was using had the canned cycle there so it was very easy to use.
    #38
  19. MJ Gurunathan

    MJ Gurunathan Adventurer

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    Hi def;

    I used the method outlined by MotorradMike, using the quill with a pin in a collet to steady the tap and keep it centered as it started the hole. For tapping fluid I just used some light penetrating oil that I had lying around in a can, it was a generic version of WD40. Worked quite well. I did make sure to go slow, though; when you are working on your own bike your heart always beats a little faster!

    As far as the welding is concerned, I deferred to the expertise of my colleague, who is a trained welder. He said to choose a filler rod for general purpose aluminum welding (4043) to play it safe.

    I am always looking to learn more, so if you see something that wasn't quite right or if you have some experience to share do let me know. I think I've learnt a hell of a lot from this little incident! I just hope someone else benefits from the collective expertise here.
    #39
  20. def

    def Ginger th wonder dog

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    With patience and wisdom and some grit thrown in for good measure, you turned a bad situation into one with a good outcome. Many less skilled would have either incurred a large repair bill or sold their bike.

    I would let the dealer know of the success of your repairs and somehow convey to him that you have no faith in his skills and his business practices don't inspire customer loyalty or patronizing his business...in other words, he should be ashamed of the way you were treated (not to mention your bike).

    Did the dealer give you a bill for breaking your motorcycle?

    Continued success.

    73
    #40