getting the gearbox out for repairs on my '96 1100RT

[schneeman]

Hi all,

I finally started the long-awaited work on the bike to fix the gear-skipping issue i've had since i bought the bike a bit over a year ago. I purchased a second hand M97 gearbox with something like 90tkm on it (don't recall exactly), and the plan is to take the input shaft from the old one and put it in the M97 to make one perfect transmission. After reading countless posts on the forum and getting a lot of helpful advice from many of you i feel ready to go. I thought i will document the process here, like so many before me.

Unfortunately i do not own a garage, and i have to work in the one i rent together with 3 other people, it's just a concrete shed, no electricity or heating, so conditions are a bit spartan, but i try to make it bearable by using a looong extension cord to get some electricity in there to power a small heater and 2 small lamps and other power tools like heat gun, drill etc.

I have to shift the heater constantly to get the warm(er) air blowing to where i am at the time, same with lights, so everything takes longer that it would otherwise. Add to that no storage space, and the logistics of the whole process increases the effort quite a bit. When the temperature gets below zero i cannot sit there more than a few hours before i start shivering The fun part is that if i try to use too many appliances the extension cord overheats and switches off, so to heat some bolts with a heat gun i had to switch everything but the neon lamp off (the heat gun kept me warm ) All the above adds to the experience, to keep the spirits up i think of the guys who had to fix their BMWs on the easter front during WWII

Anyway, i can take my time doing this, so no problem.

This is by far the most complex repair attempt i have undertaken, previously changed the Hall sensor, starter and fuel filter on a 1100R. But as i'm pretty anal about everything, i remain optimistic.

 

Here's the work place (it is snowing)

 

after some time... (the garage is normally empty apart from the bikes, all the stuff you see is what i brought in for the job)

 

I use the door frame to hang a rope and neon lamp from, so that i can position the lamp exactly where i need it to see what i am doing

I sit on a cardboard box filled with some stuff, very comfy, or on a thin styrofoam sheet directly on the floor when i need to get lower. Most of the time i'm on my knees, sometimes even lying on the floor. Blessed be whoever fitted the place with a carpet, rather unusual commodity for a garage

 

Today i got almost got to the gearbox, just the swingarm left and then i can take the tranny off and work on it at home.

 

 

 

The good news is that the final drive seems to be ok, was worried about that too, when i first changed oils after purchase it came out opaque (even though previous owner said he had changed it recently) , didn't check for particles back then, so i was relieved to see clear oil with no particles after a year of riding. Have no unusual play in the FD, splines are perfect, even had some lubricant still on them. So at least i don't have to rebuild the FD

Hope the splines on the tranny input shaft are ok as well, i will still need it !

 

I will keep updating this thread as i continue the work, that's it for the first installment.

 

One more thing, I want to thank everyone on this forum, all those who answered my questions and encouraged me to undertake this task (unless i fail, then i will blame you !! )

Cheers !

 

[Edgar]

Take a minute to strap the front wheel to the center stand to prevent the accidental collapse of the stand. DAMHIK. Good luck!

[schneeman]

thanks for reply and advice Edgar !

 

[David R]

I use a rug too. It really helps.

 

Best of luck

 

David

[dan cata]

I changed the gearbox too, but made a direct swap, instead of opening both of them and putting in the best parts.

 

Next thing I need to do is change the FD to a GS one, for ratio purposes

 

Thanks,

Dan Cata

[schneeman]

thanks for the comments !

 

swingarm and drive shaft are out, took forever to heat the pins enough to remove them safely, and still the big pin on the right was very hard to start going, both in the swingarm and the final drive.

You can see how dirty the engine block is, previous owner's maintenance was a joke, among other things he pinched the seal in the spark-plug tunnel in the right cylinder head, so that oil was spraying out, and by the looks of it was driving like that for quite a while. The amount of gunk is unbelievable, i will take this opportunity to clean it as much as i can now that i have better access to it.

 

 

 

[nrp]

[Take a minute to strap the front wheel to the center stand to prevent the accidental collapse of the stand. DAMHIK.]

DAMHIK too! Felt really stupid making that mistake.

[Limecreek]

Nice work so far! On reassembly of the swingarm pins; make sure you clean every bit of the old threadlock from the threads before reassembly.

[eddd]

Nice work so far! On reassembly of the swingarm pins; make sure you clean every bit of the old threadlock from the threads before reassembly.

 

+1

 

This is very important. I found the best tool for this was a Dremel or other brand (I really like my Black and Decker model) with the wire brush attachments. You'll likely go through several brushes. If loctite is still coming out keep going. Less expensive brushes can be purchased at Harbor Freight or through Amazon (link).

[schneeman]

Thanks guys, appreciate your advice !

I already cleaned all the threads from the old loctite using a heat gun and brass wire brush. I take my time and inspect & clean every part i remove, makes my progress slower, but hey, winter is loooooong (and i really enjoy this sort of work)

cheers !

[SKYGZR]

Looks like tying the nose wheel to the stand ain't gonna work with all those wood blocks in the way.

[dan cata]

Where is all that oil on the engine lower side come from? And the center stand too... It can't come from the spark plug seal... I think it comes from the middle of the engine, where the 2 sides meet. Use a couple of brake cleaners and clean everything good in there and keep an eye on it after it's all together

 

Dan.

[schneeman]

Where is all that oil on the engine lower side come from? And the center stand too... It can't come from the spark plug seal... I think it comes from the middle of the engine, where the 2 sides meet.

 

Hi dan

I believe the oil came from the right cylinder head spark plug seal, as i said before, the oil is only on the right side under the cylinder, and from there it also got a bit to the back with the moving air while driving, centre stand and all. It correlates very well with the location of the "pinch" in the old seal. Now it looks very fresh and "oily", since i sprayed it with engine cleaner spray to loosen it up and eventually remove with a brush. No fresh oil came after i replaced the spark-plug seal in the right cylinder a year ago. The oil had been accumulating and collecting dirt for quite a while since the previous owner didn't pay much attention to the bike - he treated it like a bus, get on, go where you want, get off, done.

 

 

Looks like tying the nose wheel to the stand ain't gonna work with all those wood blocks in the way.

 

yeap, no way to do it in this configuration, but the block prevents the bike from tipping forward, i made sure it is stable to small/medium perturbations, and i try not to cause big ones (like tripping and falling on the bike for example )

 

I have successfully removed the gearbox and clutch today without any problems, have to clean the splines to inspect them in detail, but from what i saw so far they look brand new. The clutch disc looks ok, 5.6mm thick, so i will not be replacing it.

Tomorrow i plan to clean the gearbox so that i can open it up.

 

One this got me thinking a bit, one of the gearbox bolts removed a little bit of the thread from the engine block. I didn't have to struggle with it, all of them came out easily, but then i saw something that looked like when you have loctite on a bolt, and upon removing it it turned out to be the thread, aluminum "coil" about 5mm long, roughly 5-6 loops. Logically, it has to be the thread from the top of the hole, otherwise it would have been removed from the bolt by the remaining thread when unscrewing the bolt (not sure if it's clear what i mean). Anyway, since there are 6 bolts and there is still some thread left in the engine block for that particular bolt, i hope it's going to ok. Don't have much choice anyway...

 

Gearbox removed

 

 

Clutch removed

[schneeman]

Clutch

 

 

[nrp]

{One this got me thinking a bit, one of the gearbox bolts removed a little bit of the thread from the engine block. I didn't have to struggle with it, all of them came out easily, but then i saw something that looked like when you have loctite on a bolt, and upon removing it it turned out to be the thread, aluminum "coil" about 5mm long, roughly 5-6 loops. Logically, it has to be the thread from the top of the hole, otherwise it would have been removed from the bolt by the remaining thread when unscrewing the bolt (not sure if it's clear what i mean). Anyway, since there are 6 bolts and there is still some thread left in the engine block for that particular bolt, i hope it's going to ok. Don't have much choice anyway...}

You might want to see if you can thread the block hole a little deeper with a bottoming tap, and/or get a longer bolt for this one location. You could even cut the bolt to the max exact length possible.

 

This sort of thing only gives you one chance before making a heckuva lot of extra work.

[Selden]

Even though I replaced the clutch on my 99 RT last year, I don't know how much the transmission weighs, because I built a dolly for the task. I strapped down trans and swingarm tightly, and used a small bottle jack to make minute height adjustments when I was putting things back together; as a result, lining up the transmission with the clutch rod was relatively easy, with no worries about bending it due to misalignment. I also used a tiedown strap to slowly pull the transmission toward the engine: move a little, measure, move a little more, measure.

[schneeman]

You might want to see if you can thread the block hole a little deeper with a bottoming tap, and/or get a longer bolt for this one location. You could even cut the bolt to the max exact length possible.

 

This sort of thing only gives you one chance before making a heckuva lot of extra work.

 

thanks nrp, didn't think about that. If in fact the hole is longer than the length of the bolt that was there, then bottoming tap plus a longer bolt might be the way to go.

[nrp]

BTW - Release the clutch several times during the engine-transmission pull-up, even if you use a clutch pilot alignment tool initially. It just might be that dragging the clutch disk across the flywheel otherwise is what is causing these alignment problems. The clutch housing on the R bikes is thin and maybe quite deformable due to the starter opening.

 

FWIW - This is just a pet suspicion of mine.

[Selden]

BTW - Release the clutch several times during the engine-transmission pull-up, even if you use a clutch pilot alignment tool initially. It just might be that dragging the clutch disk across the flywheel otherwise is what is causing these alignment problems. The clutch housing on the R bikes is thin and maybe quite deformable due to the starter opening.

 

FWIW - This is just a pet suspicion of mine.

I share the same suspicion.

[greenrider]

How many miles are on your 1996?

Its great to see that the splines are in such great condition.

I bought a 1997 R1100RT with 109000 km (67700 miles). And reading how the spline is a common weak spot its always in the back of my mind that it might let go anytime. And no sure if I should pull it apart to re-grease the spline.

[schneeman]

BTW - Release the clutch several times during the engine-transmission pull-up, even if you use a clutch pilot alignment tool initially. It just might be that dragging the clutch disk across the flywheel otherwise is what is causing these alignment problems. The clutch housing on the R bikes is thin and maybe quite deformable due to the starter opening.

 

FWIW - This is just a pet suspicion of mine.

 

Thanks for another good tip nrp, will remember that.

As for the damaged threads, i measured that there is about 4 mm of depth left in the bolt hole, so i will try to exploit that. Nice.

 

 

How many miles are on your 1996?

Its great to see that the splines are in such great condition.

I bought a 1997 R1100RT with 109000 km (67700 miles). And reading how the spline is a common weak spot its always in the back of my mind that it might let go anytime. And no sure if I should pull it apart to re-grease the spline.

 

My '96 is now about 60tkm, not so much. From what i can tell previous owner was not an abusive rider, just low on maintenance. Before that no idea.

The clutch splines were dry, while FD ones were still lubricated. I was relieved to see the condition of all splines on my bike.

 

BTW, what do i use to lubricate the seals and rubber sleeves ?

there was some white stuff on them, not sure what it is.

 

Some pics of the input shaft splines

 

 

 

 

Now the real fun begins...

 

[nrp]

Just pull the starter & carefully see how much wear/clearance there is on the spline faces. You might be pleasantly surprised & be able to get by with a hypodermic lube. It sure beats being suddenly stranded somewhere else. Think of a spline as an inside & outside 1:1 gear set. If there is any relative motion, it will fret and wear. If there happens to be no relative motion, the "gear" faces won't wear.

 

Remember - if you happen to have good spline alignment, you really don't want to take it apart though lubing is really essential. Just be very very careful not to have any excess grease get onto the clutch facings, yet a tiny amount of fresh grease on all faces of the spline teeth.

[nrp]

BTW - Release the clutch several times during the engine-transmission pull-up, even if you use a clutch pilot alignment tool initially. It just might be that dragging the clutch disk across the flywheel otherwise is what is causing these alignment problems. The clutch housing on the R bikes is thin and maybe quite deformable due to the starter opening.

 

FWIW - This is just a pet suspicion of mine.

 

Thanks for another good tip nrp, will remember that.

As for the damaged threads, i measured that there is about 4 mm of depth left in the bolt hole, so i will try to exploit that. Nice.

 

 

How many miles are on your 1996?

Its great to see that the splines are in such great condition.

I bought a 1997 R1100RT with 109000 km (67700 miles). And reading how the spline is a common weak spot its always in the back of my mind that it might let go anytime. And no sure if I should pull it apart to re-grease the spline.

 

My '96 is now about 60tkm, not so much. From what i can tell previous owner was not an abusive rider, just low on maintenance. Before that no idea.

The clutch splines were dry, while FD ones were still lubricated. I was relieved to see the condition of all splines on my bike.

 

BTW, what do i use to lubricate the seals and rubber sleeves ?

there was some white stuff on them, not sure what it is.

Beautiful condition! I used Honda Moly 60. Others use something called Guard Dog 60. Should be black from being high moly disulphide and incredibly sticky. Put a thin coat w a brush on both surfaces but don't allow any to get or spin onto the clutch faces!

[schneeman]

Well, actually after measuring again a few times it seems that the hole with the damaged thread is 25mm deeper than where the current bolt reaches, while the thread goes all the way to the bottom, so instead of using M8x55 as it is now i can just use a M8x75 bolt.

[schneeman]

Today took the M94 gearbox apart. 35 mins in the oven at 100 degrees and it all came apart without problems. Notice the silver metallic color of the oil.

 

 

Apparently this M94 is one from the last batch where they already had clean bearings on the input shaft, if that means it's directly interchangeable with the M97 input shaft it would save me some work.

 

Axles out:

 

 

 

Shifting forks and roll out :

 

 

Shafts out:

 

 

 

 

[smiller]

That last picture is a classic M94 worn shift fork which was causing your skipping-gear issue. But the M97 has an endemic problem of its own (eating rear input shaft bearings) and you might want to check your replacement M97 before you install it.

[schneeman]

That last picture is a classic M94 worn shift fork which was causing your skipping-gear issue. But the M97 has an endemic problem of its own (eating rear input shaft bearings) and you might want to check your replacement M97 before you install it.

 

yeah, that's what this thread is all about ...

[schneeman]

M97 gearbox:

 

 

I can see it's been opened before, one lock clip is missing, the sealant between the two halves of the case was applied in excess and differs from the original, but what worries me most is that there are some small metal shavings present in the oil in the corners of the housing. Not sure where they came from, upon inspection the shifting forks look ok, dogs look ok, everything looks ok. WIll take a look again. Maybe it has been overhauled after the usual M97 input shaft bearing failure, can that produce metal shavings ?

 

 

input shafts: top M97, bottom M94 (last batch, with clean bearings)

 

 

The shafts differ a bit at the bottom end, the end of M94 is tapered and more exposed. From what i saw so far it shouldn't make a difference, but will double check. Have to measure them precisely to find out if and what adjustments need to be made, so far the spacings seem identical.

 

 

[smiller]

You pretty much have to pull the rear bearing on the M97 shaft if you want to do a proper inspection as early bearing damage can be invisible when assembled.

[schneeman]

You pretty much have to pull the rear bearing on the M97 shaft if you want to do a proper inspection as early bearing damage can be invisible when assembled.

 

Yeah, i might do that later just to see if there's any damage, for now priority is to build the M97 back using the M94 input shaft.

[smiller]

Oh yeah, forgot you were swapping them out. Nevermind.

[schneeman]

upon inspection of the gears i discovered that one of the wheels on the intermediate shaft is damaged, seems to have been eaten out a bit, this happens on one side of the "teeth" only, and in a couple of places on the wheel, in a progression, meaning the damage is getting larger from one tooth to the next, like in the pic below. It is also always on the same location on the teeth, so it's likely to be caused by misalignment with the corresponding wheel on the other shaft.

I think that's where the metal shavings came from.

 

 

 

So my question to all gearbox gurus out there, what causes this, some misalignment, wrong clearances, or material fault ?

 

And how serious is it, i mean the damage is not very deep, but if it continues like this then i am looking at a failure down the road.

It seems i cannot order just the wheel and would have to buy a complete new shaft if it turns out i cannot reuse this one. And that costs a lot of money new from BMW, about 1000$, which probably makes buying another used M97 sound like a better option if it comes to that. Damn, i was hoping this M97 would solve my problems...

 

[nrp]

Definitely not a clearance problem, probably not an alignment problem, but looks to me like a material defect or most likely a heat treat problem.

 

The part is probably made from carburized 8620 (or similar) steel - whatever the German equivalent is.

 

Is the smallest "wart" (actually inverted wart) in the root of the gear tooth, or is it actually on the contact surface? It looks in the photo like it is in the root. I assume that is just a photo artifact as I'd expect it to be a spalling type fatigue failure on a loaded face.

 

My opinion FWIW

 

Niel Petersen

Mech Engr (retired)

[nrp]

After some more review, the location of those marks make me wonder about the tooth profile of the mating gear. It is as though the mating gear has excessive material on the tips of the teeth making an extra hard line contact on the roots of the pictured gear.

 

When does the pictured gear carry power (i. e. 1st gear or 5th)? Is this damaged gear face the most highly loaded in the whole cluster?

[schneeman]

Definitely not a clearance problem, probably not an alignment problem, but looks to me like a material defect or most likely a heat treat problem.

 

The part is probably made from carburized 8620 (or similar) steel - whatever the German equivalent is.

 

Is the smallest "wart" (actually inverted wart) in the root of the gear tooth, or is it actually on the contact surface? It looks in the photo like it is in the root. I assume that is just a photo artifact as I'd expect it to be a spalling type fatigue failure on a loaded face.

 

My opinion FWIW

 

Niel Petersen

Mech Engr (retired)

 

After some more review, the location of those marks make me wonder about the tooth profile of the mating gear. It is as though the mating gear has excessive material on the tips of the teeth making an extra hard line contact on the roots of the pictured gear.

 

When does the pictured gear carry power (i. e. 1st gear or 5th)? Is this damaged gear face the most highly loaded in the whole cluster?

 

Thanks for your comments nrp, as a mechanical engineer you surely have more experience with this stuff than me, so it's good to hear your opinion.

The warts are not exactly in the root, i would say lower part of contact surface. The pattern you see in the pic is repeated 2-3 more times around the wheel, always a few teeth involved and the size of the damage increases as you go from one tooth to the next. From what i can figure out the wheel is under load in second gear, nothing out of the ordinary can bee seen with naked eye on the matching 2nd gear wheel on the output shaft. It does look like spalling fatigue i guess.

What would you advise ?

[nrp]

I now understand that there are three separate but somewhat similar areas of such 3 tooth failures, and that here you have pictures of only two of them. Did you get equivalent sized particles or chunks out of the oil? or did everything get chewed up to fines?

 

Frankly, if it was my bike, given the service that I'd expect from it (but I'm 74), I'd quietly put it back together with new bearings & just monitor the noise and the drain oil more frequently for signs of further failure. I don't think the assembled transmission will be any noisier - yet at least for now.

 

Since a new replacement is $1K (ouch!), you might want to keep an eye out for a used one from BeemerBoneyard or similar. Besides, then you could relube the clutch ID spline.

 

But this is just my opinion. In something like this, gurus such as experienced service guys can tell you if they have seen this before (yikes!) and are probably better at crystal balling the likelihood of future failure.

 

The more I think, it is probably a material failure. It would be interesting to see if there are initiating crack indications at the roots of other teeth in that gear. Do you have any easy access to Magnaflux or Zyglo? If there are cracks at the root of every tooth, I would definitely replace it.

[schneeman]

I now understand that there are three separate but somewhat similar areas of such 3 tooth failures, and that here you have pictures of only two of them. Did you get equivalent sized particles or chunks out of the oil? or did everything get chewed up to fines?

 

That's correct, there is a series of such failures all around the wheel, always at the same location on the teeth, some span 2 some 4 teeth, some are smaller some larger. I found distinct metal shavings in the housing (bought the box without oil in it) about 1mm in size.

 

As tempting as it is to reuse the shaft i am looking around for a replacement. I would just think about it every time i ride and that would definitely spoil the fun. Will cost additional $$ but worth it for the peace of mind, and still much less expensive than a new/overhauled/used gearbox. I am a bit on a budget but what can you do. Don't want to be doing this again in a year or so if the shaft breaks. If i cannot find any spare parts soon then i might go with the damaged one and just pray it holds. Thanks again for your opinion nrp, much appreciated.

[Twinsig]

Great thread here. Inspired to open my spare (broken) Trans. Supposedly has 5-6 gear problem.

[nrp]

More thinking. I wonder if possibly some original tramp metal was in the gearcase when it was first assembled - and then got fed thru the gear mesh repeatedly. That would explain the damage so close to the root. What are the numbers of teeth on that gear and the one it meshes to? Are they a multiple of three?

 

I once had a snap ring go thru a couple of 10 inch gears running ~5000 rpm. Ooooh boy!

[schneeman]

I once had a snap ring go thru a couple of 10 inch gears running ~5000 rpm. Ooooh boy!

 

oooops...

would like to see that, through a thick plexiglass plate though

 

 

The small and big wheels have 21 and 33 teeth, respectively, so yes multiples of 3.

Following your lead i worked out that if, for example, something was stuck to the big wheel, it would come in contact with tooth 1 of the small wheel upon first revolution, then 12th, 3rd, 15th, 6th, 18th, 9th and back with 1st. So every 3rd tooth should be damaged, and that's not the case. It might be that something was swirling around in there, but then why would only that one wheel be affected, the gearbox is supposed to have 90tkm on it, so in that time a free floating particle that got to that wheel would have gotten to all others as well. Unless it was quite dense and somehow fell from somewhere (?) between those wheels, went around a bit, caused the damage and then got spit out and into the case where it remained, until someone opened the case, saw what happened, cleaned the debris and got rid of the gearbox.

Still, given that the damage is always in the same location on one side of the teeth it is unlikely to be caused by a free floating particle, i think my money would be on your first suggestion, material fault, improper heat treatment of steel.

 

 

here are some more pics of the damage (wheel is covered in oil, so many reflections, but the damaged patches are easy to spot, everything else is a reflection):

 

 

 

 

 

 

 

 

[smiller]

I don't know what the future hold for that gearset (maybe 2 more years of service or maybe 20, who knows) but I wouldn't be inclined to try to re-use it. Another option (besides finding another M97) would be to have the shift dogs on the M94 undercut which should prevent a recurrence of the shift fork wear problem. Bruno can do this, think it runs around $300 so not the cheapest way out but should leave you with a nice transmission (in some ways the M94 was a better unit than the M97.)

[nrp]

Requoting (comments) :

 

The small and big wheels have 21 and 33 teeth, respectively, so yes multiples of 3.

Following your lead i worked out that if, for example, something was stuck to the big wheel, it would come in contact with tooth 1 of the small wheel upon first revolution, then 12th, 3rd, 15th, 6th, 18th, 9th and back with 1st. (Agree. There is no hunting tooth and each damaged tooth interfaces with only a couple of mating teeth) So every 3rd tooth should be damaged, and that's not the case. It might be that something was swirling around in there, but then why would only that one wheel be affected (I'll bet that damaged gear is softer than the mating gear. You can check them with a file), the gearbox is supposed to have 90tkm on it, so in that time a free floating particle that got to that wheel would have gotten to all others as well. Unless it was quite dense and somehow fell from somewhere (?) between those wheels, went around a bit, caused the damage and then got spit out and into the case where it remained, until someone opened the case, saw what happened, cleaned the debris and got rid of the gearbox.

Still, given that the damage is always in the same location on one side of the teeth (this could be a lube oil flow pattern) it is unlikely to be caused by a free floating particle, i think my money would be on your first suggestion, material fault, improper heat treatment of steel.

 

This failure is interesting and frankly fun from an analysis standpoint. It is a weird failure.

[dirtrider]

Afternoon schneeman

 

I really can't tell much from the pictures other than the teeth are damaged fairly deep on the tooth.

 

Being in the auto industry I have seen similar gear tooth issues & your problem looks similar to what I have seen in the past from high peak loading (rock cycles) that damage the tooth drive side. Even a low quality lubricant or lack of lubricant could start the issue but you seem to have the problem on only one gear set (a lube issue would probably show on other gears also).

 

Might also be as NRP suggested & that being a bad heat treatment or defective base metal.

 

From long time dealing with this type of problem in my job we guess (engineering level) at these gear damage problems all the time & miss the root cause about as often as we guess correctly. The only way we get to the root is to either duplicate the failure a few times under testing conditions or send the gear set to the lab for" expert" analysis.

 

The main reason I posted here is to bring up a couple of similar looking gear tooth damage issues I have seen over the years. Both were motorcycles & both were just a few teeth on one side. On the two bikes I have seen it on (neither a BMW), as far as I could determine both were heavily trailered IN GEAR & the damage was to the gear set in the gear they were trailered in. One was 2nd gear & the other was 1st gear. Trailering in gear not only loads the gear set continually in a specific area but it doesn't take long to beat the gear lube out of the contact area (above lube gears only) so the gear teeth are rattling & beating around with no lubricant cushioning. (just something else to think about)

 

[schneeman]

The main reason I posted here is to bring up a couple of similar looking gear tooth damage issues I have seen over the years. Both were motorcycles & both were just a few teeth on one side. On the two bikes I have seen it on (neither a BMW), as far as I could determine both were heavily trailered IN GEAR & the damage was to the gear set in the gear they were trailered in. One was 2nd gear & the other was 1st gear. Trailering in gear not only loads the gear set continually in a specific area but it doesn't take long to beat the gear lube out of the contact area (above lube gears only) so the gear teeth are rattling & beating around with no lubricant cushioning. (just something else to think about)

 

Hi dirtrider,

Thanks for your comment, it is a very interesting observation, i can see how trailering in gear can be bad for a gearbox. Why would anyone trail a bike in gear in the first place? Apart from maybe some strange tow scenario when you leave the bike where it shouldn't be or something.

 

This failure is interesting and frankly fun from an analysis standpoint.

Yeap, I just wish it wasn't mine to deal with

 

 

In any case, i spent 2 days searching the web for a replacement and i think i will be able to get the whole M97 intermediate shaft for 100-150 $ with shipping, depending on location i get it from. So there's hope for my wallet, i was already contemplating getting the M94 overhauled and brought to M97 specs (1200$ where i'm located).

 

 

[Twinsig]

Interesting Dirt! My orig Trans the PO gave me in the deal has about 80k on it and has a 5-6 gear problem, not sure what exactly. When removing rear lug nuts by the "book", bike on center stand, Trans in fifth gear, bla, bla, makes me wonder......

I use a short piece of 2x4 as a scotch.

[schneeman]

hmm, more issues, not sure what to make of it

 

i measured all the distances before putting the shafts in, i.e. measured the depth of both halves of the box, measured the length of the shafts (outer bearing race to outer bearing race), spent the whole afternoon doing it and it made sense, turned out the shims that were in place in the 97 gearbox were close (to my measurement precision of 0.05 mm) to give 0.1mm of end play.

What i also measured is that the 94 input shaft is 0.15mm shorter bearing to bearing that the 97 one, so i was expecting to have to put thicker shims to make up the difference.

BUT, today i installed the shafts and measured how much they protrude out of the deeper half of the box, and while the measurements for the intermediate and output shaft are close enough to the previous measurements , the input shaft seems to have only 0.15-0.2 mm clearance left. From previous measurement it should have about 1mm clearance.

Since the measurements for other shafts are close to each other, i assume it's not due to measurement mistake.

Once again the numbers, first calculated with the 1st method, meaning: sum of two depths of the box minus the length of the shaft:

94input shaft = 1mm (97shaft = 0.85mm) (shims that came with the box = 0.65mm)

intermediate = 0.875mm (shims 0.7mm)

output = 1.55mm (shims + oil guide 1.5mm )

 

Now, with the shafts installed in the deep half of the box:

Input shaft clearance : 0.15mm

Intermediate shaft clearance : 0.725mm

Output shaft clearance: 1.525mm.

 

Additionally, the input shaft has quite a radial play, due to movement in the bottom bearing. All shafts can be moved sideways a bit to give radial movement, but input has the largest. Not sure how important it is, the repair manual says to check the axial play, there's none, i believe the radial play will disappear when i install the lid.

But the end play of the input shaft is my concern, seems from the latest measurement i should not be shimming it at all, while previous, 0.15mm "longer" shaft was shimmed with 0.65mm.

I tapped all the shafts a bit with a plastic hammer just to make sure they sit in, since the box was really hot for installation they all jumped right in, no struggle. I know i am not supposed to tap the input shaft, but when i measured it and saw the result i tapped it a bit to make sure it sits properly, and measured again and again, same result. I don't feel like taking it all apart again to see if perhaps some small piece of , for example, old sealant, got in the between the bearing race and the box.

What i also measured previously is that the bottom end of both input shafts, from the bearing race to the end, are the same, so it should not be the case that the 94 is longer and the outer race of the bottom bearing is not seated all the way in.

I know that the previous open-bearing on those shafts were preloaded by 0.2mm if i'm not mistaken, but the clean ones should not be.

So i am really not sure what to do

to shim or not to shim, that is the question

[Selden]

So i am really not sure what to do to shim or not to shim, that is the question

Sounds like a question for Anton Lagardier...

 

Thanks for your extensive description of this project. I don't ever expect to attempt a transmission rebuild, but it's been very informative.

[schneeman]

ok, quick update, in desperation i took an aluminum rod with some plastic cap on the one, positioned it agains the outer race of the bottom bearing of the input shaft, and tapped with a plastic hammer a bit on opposite sides of the bearing to try to hammer it in a bit and see what happens

Result is now the clearance is ~ 0.7mm

So i guess math is correct, and the bearing simply doesn't sit in there as well as it could. With this clearance i might just put the 0.65mm shims that were in there, but since i'm anal i will maybe heat the box a bit in the area of the input shaft bearing and tap it a bit more to see if it goes deeper, don't want to end up with too much end play once the box heats up while riding. The predicted clearance should be about 0.9mm, so only 0.2mm to go...

 

Thanks for your extensive description of this project. I don't ever expect to attempt a transmission rebuild, but it's been very informative.

 

You're welcome

It's not wrenching at its best, but i found tons of helpful threads and people on this forum and so i thought i can take a bit extra time to record my struggles in case someone else finds it useful/entertaining. That of course beside asking for help every 5 mins

cheers

[schneeman]

After some more gentle tapping i got the clearance to what originally predicted (1mm). Not very scientific to accept the result one expected in the first place, but i think i'm satisfied and will shim it with 0.9mm. Hope it won't explode in my face down the road

 

Apropos the damaged intermediate shaft, i ended up buying a second-hand replacement of ebay, feel very lucky since it was the only one i could find locally, paid 75 euros with shipping.

[smiller]

Hope it won't explode in my face down the road

I don't think it will. Much is made of gearbox shimming but basically what you're looking for is to have no preload on the bearings (if they are the caged ball bearing type) but also not have too much slop, at operating temperature when the shafts are free to float. Many like to attribute shift quality, etc, to stuff like this but I doubt it would have much of an effect unless it was pretty far off.