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Thread: Revelations on spline wear

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    Curmudgeon nrpetersen's Avatar
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    Revelations on spline wear

    I reposted with more pictures
    Last edited by nrpetersen; 06-08-2010 at 02:49 AM.

  2. #2
    Curmudgeon nrpetersen's Avatar
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    I have posted in the past on my theory of clutch spline failures being caused by manufacturing errors in the clutch housing. Others have adjusted the radial alignments with various schemes, but now I'm starting to wonder if maybe there is an additional damage result from dragging the clutch disk around the flywheel face.

    This was to be a writeup suggesting a way to make fixturing and measure the alignment of a disassembled transmission to the engine on BMW R1100 series bikes. The idea was to make new alignment pins with a small offset to shift the transmission as required to minimize spline wear. But the project grew and with it, I found a new cause of premature spline failure, and maybe serious consequential damage.

    The subject bike was a 1996 R1100RT with ~55K miles and a fully stripped out clutch-transmission input spline. The project was to make a fixture that could use a dial test indicator ($30 at Grizzly Tool) that would simplify run out measurements of the transmission input bearing housing bore with respect to the crankshaft rotating axis. Before, this has always been a problem because standard purchased magnetic bases are way too bulky to fit and swing in the clutch housing, as well as too flimsy to give accurate readings.

    I made a fixture which used the two hard disk rare earth magnets from a dead hard drive head (everyone has a few of these left around...) to span three of the flywheel bolt heads. A short piece of 1/2 inch conduit was used to project through the transmission input bearing housing, terminating in a 45 deg angle. A crude dovetail was hacksawed into the end of the 1/2 inch conduit, a slot was cut and a small screw used to give compliance necessary to mount the dovetail of the dial test indicator.



    The conduit was brazed to a flange, and the whole mess was epoxied to two hard drive magnets (take your mechanical watch off as you will find these thing are incredibly strong!).



    The distance from the bolt head face to the indicator reading point ends up being about 3 5/8 inches for the R1100.



    The fixture has to be pushed thru the input bearing hole, and the indicator assembled on it before the clutch bell housing is assembled onto the engine. This is because the indicator won't pass thru the input bearing housing bores.



    Final adjustments to get the indicator in its limited +/- .030 inch range can be made by carefully sliding the whole mess on the flywheel bolt heads. Note that the bearing housing bore doesn't quite make a full circle so you have to sweep the indicator back and forth.



    This setup was so rigid and it fit first time! Sure enough facing forward looking at the dial test indicator from the bike's rear, the bearing bore showed .013 inch total run out as the crank was slowly rotated.


    The measurements were very repeatable. Based on the crankshaft centerline, the transmission was displaced towards the 7 o'clock position by .0065 inch.

    But.........

    On a hunch I also measured the main bearing clearance while prying different directions on the flywheel with a screwdriver. Still measuring at the transmission input bearing bore, I found that the main bearing clearance was a whopping .008 inch! - again in the 1 to 7 oclock direction. In the 10 - 4 o'clock position the main bearing wear was only about .002 inch.

    The books say new main bearing clearances should be in the range of .0008 to .002 inch, with a service limit of .004 inch. This is at the bearing shell itself whereas I was measuring cantilevered out the back of the engine a few inches.

    Now - It does appear as though the transmission axis is below the average crankshaft axis by a few thou. But why should the wear on the mains be in the 1 o'clock -7 o'clock direction also? I'd think the maximum wear axis should be in the 9 o'clock-3 o'clock direction.

    Question - Is there an alignment issue here? I think there is and always has been. Has it caused the main bearing wear? I am very suspicious that it has as otherwise I see no reason for so much wear in such an odd direction.

    Question - What kind of main bearing wear do other overhauled engines show? Has anyone else that has gone through the agony of measuring the run out checked the main bearing wear? I'd now say they should definitely do so.


    In the meantime, I have no further use for my fixture. If anyone is interested, PM me. You furnish the dial test indicator!
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

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