reasons for pivot bearing failure? - BMW Luxury Touring Community
 
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post #1 of 9 Old Nov 8th, 2012, 9:45 am Thread Starter
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reasons for pivot bearing failure?

I recently rebuilt my final drive and when I opened the drive I realized that the pivot bearing cage was chewed up.

I observe that the reason for the roller bearing failure is the extra shim. What is the reason for pivot bearing cage to fail?

Amish.

1996 Kinetic Pride 75cc - First motorized cycle at age 16.
2002 Yamaha Enticer 125cc - First brand new cycle bought from the first salary at age 20.
1984 Honda Shadow 1100cc
1999 BMW K1200LT
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post #2 of 9 Old Nov 8th, 2012, 12:08 pm
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Re: reasons for pivot bearing failure?

If you mean the two that connect it to the swing arm, it is because a tapered needle roller bearing just does not work well in this application. They develop notchiness as they beat aganst the races with little rotational movement. I replaced mine with Rubber Chicken Racings solid oiltite version bearings. If you do use them, you reduce the preload on the them to about 1/2 what the needle bearings call for.

If you mean the taper bearing on the hub unit - it was taken out by the creeping race on the pinion shaft. This is based on the pictures you had submitted earlier.

John
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post #3 of 9 Old Nov 9th, 2012, 8:52 pm Thread Starter
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Re: reasons for pivot bearing failure?

Thanks John, I now realize I am asking about the tapered needle bearings.

I am not asking about how to fix it but whether we know why they fail?

1996 Kinetic Pride 75cc - First motorized cycle at age 16.
2002 Yamaha Enticer 125cc - First brand new cycle bought from the first salary at age 20.
1984 Honda Shadow 1100cc
1999 BMW K1200LT
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post #4 of 9 Old Nov 10th, 2012, 2:35 am
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Re: reasons for pivot bearing failure?

Quote:
Originally Posted by LTFan
Thanks John, I now realize I am asking about the tapered needle bearings.

I am not asking about how to fix it but whether we know why they fail?
I don't think that the tapered needle bearings are very robust for that application, however, I suspect that proper assembly (torqued preload) is critical to maximizing their lifespan.
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post #5 of 9 Old Nov 10th, 2012, 5:49 am
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Re: reasons for pivot bearing failure?

The tapered roller bearings in the pivot fail because they are not actually performing (in that application) as per their intended design. Any rolling element bearing must have its rollers or balls rotating 1.5 revolutions minimum. This is in an oscillating application of course. Our bearings in both the swing arm pivots and the rear paralever pivot joint would be lucky to see the rollers turn 1/2 a revolution. In this application, to maximise the life it is imperative that the bearing be 100% packed with an extreme pressure grease. That way, when a roller moves it must push through lubricant. If this is not the case then false brinelling will quickly occur and this is the notchy feeling we all talk about. I'm lucky, we use a 1000 cst. base oil grease with a tacky additive in my industry, it works a treat in swing arm and steering head bearings. For the record it is Castrol Optimol Optipit, anything similar will be fine. Hope this helps.

Dennis
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post #6 of 9 Old Nov 10th, 2012, 8:15 am Thread Starter
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Re: reasons for pivot bearing failure?

Thanks. That makes sense.

After 3 weeks of part time work and help from the forum I have managed to fix the FD. I have changed the tapered pivot bearings and the roller bearings, removed the thinner shim and reassembled the drive. It was a therapeutic experience. Before the FD issue I used to feel that the FD failure would mean the end of this bike for me but now I realize its not impossible to fix and I have much more confidence in the bike being able to cross very high mileage. I did not perform the accurate shim measurement techniques. I have only removed the thin shim.

Thanks everyone.

Amish.

1996 Kinetic Pride 75cc - First motorized cycle at age 16.
2002 Yamaha Enticer 125cc - First brand new cycle bought from the first salary at age 20.
1984 Honda Shadow 1100cc
1999 BMW K1200LT
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post #7 of 9 Old Nov 10th, 2012, 10:35 am
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Re: reasons for pivot bearing failure?

Quote:
Originally Posted by LTFan
.... I have managed to fix the FD. I have changed the tapered pivot bearings and the roller bearings, removed the thinner shim and reassembled the drive..... I did not perform the accurate shim measurement techniques. I have only removed the thin shim....
Amish,
At the risk of beating a dead horse and sounding like a broken record to frequent readers of this board, removal of the thin shim (where it exists) is something I have suggested as a quick fix and is no substitute for proper preload set up. While many failed final drives I have rebuild were over shimmed in the range of 1.5-2.0 mm not all fell into this range. Some more, some less. And while most of the thinner shims, (again where they exist as only about 50% of final drives are set up with 2 shims) are the 1.5 mm shim sometimes the thinner shim is 2.0 mm. In the case where a final drive is set up for 5.0 mm shim thickness there will be a 20. mm shim and a 3.0 mm shim. In that case if you remove the thinner shim, you will be removing 2.0 mm rather that 1.5 mm.

Congrats on rebuilding your final drive; if it were mine, I'd go back some time in the future and check measurements. You might find you are lucky and are spot on, but you may find that you are either over or under shimmed. If the setup is significantly over or under shimmed, I think our mechanical engineers friends would tell us that that can be damaging to the bearing and sets the stage for failure.
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post #8 of 9 Old Nov 10th, 2012, 10:44 am
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Re: reasons for pivot bearing failure?

Just curious Amish, did you pull the pinion out and press the creeping race back into place?
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John
2009 K1300GT Red Rocket
2009 R1200GS (Gone)
2005 K1200LT Ocean Blue Blue Wizard 110 K and counting...
2006 Bushtec Turbo+2 Spell
2004 330 Ci Convertable
K4AN

Have ridden a Motorcycle in all 48
But lack DE, MA, RI and CT with the 2005 LT

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post #9 of 9 Old Nov 10th, 2012, 6:58 pm
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Re: reasons for pivot bearing failure?

My pinion needle roller inner race has also moved away fron the pinion face by approximately 1 mm (previous post) and I intend to make a tool for undoing the pinion assembly nut to correct the problem, but it's summer here in Tasmania and there is much riding to be done. The race isn't physically loose on the shaft so I'm hoping it has taken 38,000 Km's to move 1 mm, but till I do remove the FD again I'll be frequently sucking out an oil sample (Mightyvac unit) and checking for aluminium in the oil. It can usually be seen as really sparkly in bright sunlight.

Dennis
1987 Yamaha TY250R
1991 Aprilia Climber 280
1988 K100RT (the pack horse)
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