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Survey on power line failures in oil/hexheads


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I believe that many of clutch spline, final drive and transmission failures are caused by cruising on too low rpm.

Engines power culture isn´t smooth/stabile sub 2500rpm.

It causes constant brutal pulsing which is too much to handle for small bearings and shafts.

So when you´re aiming good mpg with 6th gear doing 40, you´re slowly destroying the bike at the same time.


Similar problems are familiar in many cars with 4cyl diesel engines - transmission renewals are "normal" maintenance.


All of You who have blown your powerline, what gear/rpm range you use?

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Joe Frickin' Friday

The gearbox input shaft is fitted with a torsional shock absorber to absorb the speed/torque variations from the engine, and the driveshaft also uses a rubber coupling element. With regard to final drive and driveshaft failures, I think it's safe to say that engine RPM is completely irrelevant.


Even in the case of gearbox failures, I think it would require exceptionally low-RPM operation (to the point of rider discomfort) to overload the gear teeth or bearings. The most common oilhead gearbox failure mode is not even a standard bearing failure mode (i.e. spalling of the ball/bearing surfaces); instead, the axial face of the input shaft rear bearing experiences long-term wear due to relative motion with respect to the torsional shock-absorbing mechanism.


When not traveling at 0.5 past lightspeed on my R1100RT, I tried to keep the engine RPM somewhere above 3K RPM. My R1100RT gearbox failed in the above manner at 130K miles. I also experienced a final drive bearing failure at 85K miles. I never had any problems whatsoever with my clutch/input shaft splines; even at 130K miles (when the gearbox bearing died), the splines looked brand new. If driveline pulsations were the root cause of my gearbox and final drive bearing failures, then I would have expected to see significant damage on the splines as well.

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111,000 miles on my '02 RT, and I spend a lot of time in the 3000 +/- 500 rpm range, often shifting up at 3500 rpm. No driveline failures yet.


To be fair, I'm also at low throttle openings at these times, and will downshift if I need to make more power.


Similar riding style on the R1100RT, just fewer miles at 81,000. No driveline problems to date.



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Mileage when Mitch had failures isnt anymore in unexpected/premature region.


I meant those failures found in say 40-60k region.


Boxer is behaving just nice 3krpm. Pulsing is problematic in low rpm, thats why there are torsional shock absorbers.

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I had final drive bearing failure at just over 60K miles. I use ~3000 rpm as lower limit to rev range. The motor just doesn't feel happy below that. I never lug the motor except by mistake.

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I believe that many of clutch spline, final drive and transmission failures are caused by cruising on too low rpm.


I don't think so.......I think its a design that requires too much "fine fitting" at point of manufacture. The bearing load shims are a handful if done improperly and the mis-alignment of the shafts are well founded.


This I believe is why some shops will replace these parts and have them fail again in short order. Using the factory shim, if it was wrong in the first place is asking for failure. And most shops either don't know how or don't take the time to align (or inspect alignment) of the shafts.

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The input shaft bearing failure (Helical gear chews ball bearing to pieces.) which was not rare enough on M97 R1100s seemed to be attributable to hard riding as opposed to lugging. T. Roe, S. Daly, myself, others.......

In my case, at 49K miles.

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This assumes that rear drive failures, transmission failures and spline failures are from the same cause.

I can't imagine a rear bearing having its loads significantly increased by lugging. Transmission bearings - perhaps to a small degree. Lugging to the point of serious damage to the bike should also rattle the eyeballs out of the rider.

If we accept that lugging could be a major contributor to spline failures, perhaps we might also consider hard and constant engine braking increasing wear on the opposite side of the spline.

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When my drive shaft failed at 75,000 miles, one of the bearings in the universal joint disintegrated. There was an ominous accumulation of red dust on the outside of the rear gaiter on swing arm.


I consider 3,000 rpm to be the lower limit for operation and usually am shifting down at that point. I usually cruise around 4,000, shift up around 5,000 and know exactly where the rev limiter kicks in.


It seems to me that this bearing simply failed due to loss of lubricant owing to the obvious red dust all over the remains of the bearing surface.


More than lugging the engine and drive train, I believe that this part just reached the end of its life in the 71,000 miles I have put on it in the past two and one-half years.

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