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Thread: Transmission Input Spline Wear Pattern

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    Registered User roger 04 rt's Avatar
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    Transmission Input Spline Wear Pattern


    Input Shaft Photo from Anton Largiader


    These pictures show the common pattern seen on the R1150 transmission input shafts when there has been excessive wear. Many possible causes and solutions have been identified and debated and there have been a couple good threads recently: Checking for spline wear 1999 R1100S, and tranny input shaft. Looking at the pattern of wear on the spline, which occurs inboard on the shaft and at an angle to the spline tooth, it can be hard to imagine how or why that exact shape develops. For months I've been thinking about a model for the wear pattern on the R1150 input shaft and feel that I've come up with one.

    Many assert that misalignment is the ultimate root cause of wear. It is my view that misalignment gets the wear started and other problems cause it to accelerate. The key to the pattern of wear on the input shaft is that all misalignments, whether flatness of the clutch housing/flywheel or a shift of centerline between engine and transmission, result in an angular force on the clutch-hub which gets applied to the input shaft. (Since the transmission input shaft is in a separate assembly from the engine crankshaft, there will always be some misalignment, and it isn't known how much misalignment the R1150 can handle without excessive wear.)

    The easiest way to imagine how misalignment leads to the angular force causing the wear that's observed is as follows:

    Start with a perfectly aligned crankshaft/input shaft and then lower the transmission input shaft enough for a total tilt of 1 degree from the engine end of the clutch hub to the transmission end of the hub--about 0.017". Now imagine some play in the hub/spline coupling such that the tilt can actually happen. (This model also works if the clutch-housing/flywheel are tilted but wear progresses around the shaft/hub as clutch release/reengagement changes the hub-flywheel rotary position. Also, I am only using a downward shift as that is easier to explain. Any shift yields the same results.)

    With the transmission lowered by a degree, viewed from the rear:

    --the clutch-hub splines in the 12 o'clock position are up at the engine end.

    --the hub splines at the 6 o'clock position are down at the transmission end.

    --the clutch-hub splines at 9 o'clock position press on the input shaft only at the end near the transmission and are up off the input shaft at the engine end.

    --and the hub splines at the 3 o'clock position contact the input shaft only at the engine end and are down and off the input shaft at the transmission end.

    These differing contact points lead to wear since there is extra pressure (pounds per square inch) and the surfaces change continuously as the shaft turns.

    The "give" in this system, is the sheet metal web that holds the clutch-hub to the disc. As the engine rotates, the contact points change position such that in the y-axis (12-6 o'clock) the splines are rocking up and down, end to end as the shaft turns. And in the x-axis the clutch-hub contact point moves from the engine end of the transmission spline, to the transmission end as it rotates. (And also, based on an amount equal to [1-cosine{misalignment angle}] there would be a tiny in/out motion along the transmission shaft.)

    This pattern of contact would vary continuously as the clutch-hub rotates (in a sort of figure 8 pattern) with the teeth sliding on one another at high pressure. Further, under hard acceleration, it is possible the forces are great enough that the 9/3 o'clock positions might flatten against the shaft, meaning more motion under even higher pressure. Whether that happens or not, the contact area on the splines, and hence the pressure would get very high as they pass through the 9/3 o'clock positions. That high pressure in the model is what I'm postulating leads to the wear.

    There's another factor that may speed wear once it has begun. The engine produces its torque for only about 1/3 of its rotation. That means that the torque during the 1/3 period is on average 3X the torque reaching the rear wheel. Peak torque within the 1/3 period would be even higher. The damping of these peaks doesn't happen before the hub-spline engagement, it happens in the transmission. Whether this plays a role in acceleration of the wear is a question.

    What might improve things? Better flywheel/clutch housing flatness, better crankshaft to input shaft alignment, harder materials, lasting lubrication, longer hub/spline engagement to effectively tighten the coupling and limit the range of motion. It seems each situation will be different.

    I plan to measure flywheel flatness, lubricate and possibly extend the clutch hub, all depending on what I see when I open it up, I'm at 30,000 miles.
    RB

    Damper photo from GSAddict
    Last edited by roger 04 rt; 03-16-2014 at 06:40 PM.

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    Registered User roger 04 rt's Avatar
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    Just a note: I've been a fan of Anton Largiader's posts and articles at BMWRA.org that are only available at the moment in print.

    A couple of the articles written around 2006 take some of the ideas expressed above to a much deeper level of analysis. I reread the articles last night and want to credit Anton's influence.
    RB

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    Registered User roger 04 rt's Avatar
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    Here are a great pair of photos from an advrider thread showing the complex wear pattern of hub and spline. The hub teeth wear in a straight line and the spline teeth on an angle. I attribute the spline wear to the "3 o'clock" forces.

    Edit: "Good list" of failures at early miles here: http://bmwsporttouring.com/ubbthread...r=22563&page=1


    Last edited by roger 04 rt; 03-17-2014 at 03:39 PM.

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    Registered User roger 04 rt's Avatar
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    Relative to the cause of tapered wear on the input shaft I can across this advice.
    RB


    Alto Standard Clutch Installation Instructions

    Examine the input shaft of the transmission.
    Clean the shaft with a wire brush and inspect. If there is excessive wear, replace the input shaft. For reinstallation, place a light film of white lithium grease on the input shaft. Do not over lubricate. Excessive grease will contaminate the disc facing.

    Look for evidence of engine and transmission misalignment.
    Misalignment can cause non- release of the clutch system. There are certain conditions to look for that are caused by misalignment. The pilot bearing/bushing will have more wear on one side than the other. Uneven wear or tapered splines on the input shaft or disc splines indicate misalignment. Broken cushion segments on the clutch disc are also indications of misalignment. Broken mounts, warped bellhousing, damaged vehicle frame, or a flywheel that is wobbling on the crankshaft flange mount can cause alignment problems.

    Install the transmission.
    A transmission jack is recommended to hoist the transmission in position. The transmission needs to be supported completely to avoid hanging the transmission on the clutch disc. In many cases the clutch job is ruined at this point. The transmission is allowed to hang on the clutch disc before the input shaft is in place in the pilot bearing, the result is, the clutch hub becomes bent and will now wobble on the input shaft. This will prevent a release. If a transmission jack is not available, install long guide pins in the top mounting boltholes of the bellhousing. Place the transmission on the guide pins and slide forward. These will support the transmission while you install the lower mounting bolts into the bellhousing. As you slide the transmission forward, do so slowly. Be sure the input shaft of the transmission slides easily through the I.D. of the clutch release bearing and that you do not knock the fork off of the ball stud. Install the mounting bolts of the transmission and tighten using the star pattern with three passes.


    The next article, while from a patent on a pilot bearing, has an analysis that seems relevant to us.

    From a Patent Application
    Applicant recently discovered that it was not necessarily and primarily the lack of lubricant which causes rapid failure of the pilot bearing, but rather that the apparent cause of pilot bearing failure was often due to relative misalignment between the flywheel and the transmission housing, which misalignment, even when small, often imposes excessively large loads on the pilot bearing so as frequently to cause failure thereof within a relatively short period of operation. This misalignment is generally due to tolerances in manufacture and distortion in the large housings and case members. Applicant particularly discovered that the misalignment between the transmission and the flywheel often occurs not only angularly but also radially, whereby the forward end of the input transmission shaft, as piloted within the flywheel, also tends to move both radially and angularly relative to the flywheel, thereby causing excessive loading of the pilot bearing so as to result in rapid failure thereof. Recognition of this problem and the solution thereto represents a major portion of the present invention.

    Still a further problem associated with the known flywheel and clutch assemblies has been the fretting which occurs between the splined hub of the clutch disk and the associated splined portion of the input shaft. Due to the frequent relative misalignment between the transmission and the flywheel, relative movement often occurs between the splined hub and the splinedshaft portion whenever the clutch disk is in clutching engagement with the flywheel. This relative motion thus causes a continuous sliding or oscillating movement between the associated splines of the hub and input shaft, thereby causing fretting. This has thus often minimized the useful life of the clutch hub and has required periodic replacement thereof.

    The fretting of the clutch hub due to misalignment has also been substantially minimized by the present invention since the forward end of the transmission input shaft is supported by a resilient bushing so as to be both angularly and radially floatable relative to the flywheel. Thus, the angular rocking motion of the clutch hub on the input shaft is minimized, and the fretting problem is likewise minimized, thereby resulting in greater operational life of the clutch hub.
    Last edited by roger 04 rt; 03-27-2014 at 01:20 PM.

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    Curmudgeon nrpetersen's Avatar
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    These quoted references all have a clutch pilot bearing, which minimizes the chances of severe radial misalignment. In addition, the clutch damper spring system in most other applications very possibly gives or wears some radial motion capability to the clutch hub in the event of radial loading. Our clutches have no pilot bearing but have a flex plate which is unfortunately radially very stiff.

    You raise an interesting point, that perhaps the clutch disk flex plate is being deformed on assembly. But if this was a substantial wear contributor, I'd at least expect the wear pattern to vary around the axial azimuth of the transmission and clutch disk hub spline since in service they remain locked together. This also would not explain the frequent predictable repeat failures of some high service bikes.

    On the other hand, if flywheel run out is a major contributor, it would distribute the same wear pattern around the splines just due to random lock up azimuths. Flywheel face run out is easily checked, even just visually, but I don't think it is a substantial contributor as the number of fretting cycles is only about the same as the number of clutch engagements.

    The real potential spline life killer though is radial alignment run out because the number of fretting cycles is so high (once per engine revolution forever) and the cyclic radial spline force being limited by the double-clamped friction of the clutch disk is so high.

    Alto's suggestion of using a small amount of lithium grease on assembly is naive for our application. I'd want the stickiest anti seize possible - preferably moly disulphide based.
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

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    Registered User roger 04 rt's Avatar
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    The point of my adding those to the thread is their description of the consequences of radial misalignment. The types of wear are just what we're seeing on every failed shaft.

    A pilot bearing; a full hub/spline engagement; and/or a transmission shaft that extends past the clutch disc plane are all conditions that could have mitigated the effect of misalignment.

    The lubrication should only have to meet the needs of clutch engagement/ disengagement. How long can the best grease stay in place if radial misalignment is bad? After all, the engine rotates roughly 250 million times in 30,000 miles.

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    I was reading an interesting article where spline wear from misalignment was studied. It kind of lends to what the OP was stating. What I got out of it, in our case, was our straight splines tend to turn into crowned splines, which tend to deform in the center. Causes were both under lubrication and misalignment. The interesting part was that the properly aligned spline did not deform under test. Pics are included, look familiar? It's interesting that angular misalignment shows up as wear in the center of the spline, I'd think it would be at the ends where the contact points are, but the study shows it's not so much contact as friction.

    http://www.powertransmissionworld.co...ned-couplings/

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    Registered User roger 04 rt's Avatar
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    Interesting Link, Thanks. Here is the start of the article which I think is helpful to us:

    Spline couplings are mechanical components used to connect and transmit torque between two rotating shafts. A spline coupling consists of two parts: a shaft with external teeth and an hub with internal teeth; the load is transferred from the shaft to the hub (or vice-versa) by means of a number of engaging teeth.

    Since these components are usually over dimensioned concerning both static and fatigue behavior (or at least doesn?t presents particular problems), their weak point is the wear phenomena that may affect the teeth surfaces [1], [2].

    In particular wear phenomena such as fretting wear appear on teeth surface when a relative motion between engaging teeth is generated. The relative displacement between teeth may be generated by vibrations, cyclical tooth deflection or misalignment between hub and shaft: this point has been investigated in this work

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    Registered User ratze's Avatar
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    EXCELLENT thread, thanks to all contributing. ya know, my ole guzzis never had any issues with the splines an they stayed dusty rusty dry for 100k plus before i started lubing. compleatly diff design though, my first beemer was a c model, after fussing with those splines a few times i decided to modify the clutch disc with longer rivets and a shim to enable the use of the whole input shaft. i doubt it helped in any way as to shaft wear pattern but has'ent failed yet. (32k) i have no idea what they look like as i have not looked, the bike sets in the collector end of the barn now and hardly ever gets riden. this may be the wrong pic, my eyes have gone all ta hell.
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    Here's another paper that describes everything that's been noted, like the fretting and red dust.

    http://fcp.mechse.illinois.edu/repor..._Report177.pdf

    It's going to take awhile to get through this and imagine it's not something I'll read in bed. He talks about mostly dry clutches. Fretting happens early and it's the initial wear that set things up down the road - if you can make it past the initial break in not many problems are found later on. This makes sense to me; I remember when I was a kid the old time garage mechanics used to rebuild rear diffs using absolutely no specialty tools to set the preload. They would get it close by feel - and then install the diff and jack the back end of the vehicle up. With the tires off the ground, the vehicle would be started and run no-load in high gear at about 3Krpm for half a day. (Yes, this was as scary as it sounds!) I had a pickup done this way and it's still on the road as far as I know. I'm not suggesting actually doing this, but just to point out initial break in. I imagine the break in for most bikes happen the moment they are taken off the showroom floor - and hammered through the gears to early breakdown.

    The author makes a good point, lubing perfectly aligned splines doesn't do much. A little misalignment does a better job of holding the lube in place. He brings up a couple solutions and back them up with reference; plating the splines with copper or silver help with initial break in, and another proprietary coating, (page 16) WC/C. The answer to the question is probably in this report someplace - don't think I'm smart enough to figure it out though!

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    Registered User jnrugg's Avatar
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    Forgive me if this is out of line, but...
    I am past the 40k miles since my splines were done by a master mechanic.
    It went to bed for the winter shifting as good as the day I picked it up after the service.
    From reading in other areas many are suggesting lubing @ 40k.
    Should I do so or wait until shifting starts to suck?
    I ask because it's not something I can or will do but have a mechanic do it.
    There are other things I need done right now such as suspension replacement.

    Thanks!

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    Registered User ratze's Avatar
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    I remember when doing the c alot of these things discused in this thread came to mind, but my no how is very limited. wouldent know what to do with the tools if i had em, having said that. the best i could come up with is a 1100s gearbox with a rt clutch setup. because the c model had a huge clutch cover on it that weighed in at about 8lbs.(man hole cover). keeping in mind that my beemer experence is very limited,so i thought the lighter weight would allieviate some of the shaft wear. hmmm,,,the modifyed disc, the extra gear. very nice input shaft, ect. i did have the slave off of it on account of the lil pilot bearing going bad, dono if i greased it on assembly though. hmmm.
    The pursuit of reality at all cost.

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    Curmudgeon nrpetersen's Avatar
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    In the end though the author points out that the most damaging spline alignment issue is radial (coupling) alignment around and after the author's page 140. And that a small amount of misalignment can be tolerated, but the amount of radial (coupling) misalignment that will cause wear problems is only a couple of thousandths.

    His numerical results have to be colored by the comparatively short fatigue life he generally used. As RogerRT pointed out, we are dealing with 200+Million cycles in ~50,000 miles. In addition we already have one element (the crankshaft) running & floating in a fluid bearing that will cause some potential alignment issues in itself.

    At least in many cases our Oilheads do last.

    He really worked for his MS degree.........
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

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    Registered User roger 04 rt's Avatar
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    Quote Originally Posted by sjensensr2 View Post
    Here's another paper that describes everything that's been noted, like the fretting and red dust.

    http://fcp.mechse.illinois.edu/repor..._Report177.pdf

    It's going to take awhile to get through this and imagine it's not something I'll read in bed. He talks about mostly dry clutches. Fretting happens early and it's the initial wear that set things up down the road - if you can make it past the initial break in not many problems are found later on. This makes sense to me; I remember when I was a kid the old time garage mechanics used to rebuild rear diffs using absolutely no specialty tools to set the preload. They would get it close by feel - and then install the diff and jack the back end of the vehicle up. With the tires off the ground, the vehicle would be started and run no-load in high gear at about 3Krpm for half a day. (Yes, this was as scary as it sounds!) ? ...
    That is a tremendous document. It brings to light just how many complicated interacting factors there are in defining the true wear problem on the input spline.

  15. #15
    Registered User roger 04 rt's Avatar
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    Quote Originally Posted by jnrugg View Post
    Forgive me if this is out of line, but...
    I am past the 40k miles since my splines were done by a master mechanic.
    It went to bed for the winter shifting as good as the day I picked it up after the service.
    From reading in other areas many are suggesting lubing @ 40k.
    Should I do so or wait until shifting starts to suck?
    I ask because it's not something I can or will do but have a mechanic do it.
    There are other things I need done right now such as suspension replacement.

    Thanks!
    Is have your mechanic look in the starter port and tell you how much play there is at the clutch disc perimeter. Then if the play between the clutch hub and input shaft was small I'd let it go ... At least that's how I'm procrastinating my own situation ...

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