Taper Bearing Preload

Changing the rear tire on my ’84 R100RS I discovered a bad rear wheel bearing.

The process of learning how to remove, install and adjust new bearings was aided by Duane Asherman and Robert Fleischer.  Both men have made exhaustive studies of this service, documented them on the web and were very kind to assist me via email.  And Robert Fleicher’s encyclopedic http://www.bmwmotorcycletech.info covered both setting preload and removing and installing bearings in extraordinary detail.

I was fortunate to discover that my 1984 model R100RS has wheels that allow removal and installation of wheel bearing without first heating the hub.  Removal was a simple matter of using a 30mm blind bearing puller, and installation using a standard race installation driver  – both quite inexpensive tools on eBay or Harbor Freight.

The bearings on my R100RS’s wheels are taper bearings – similar to the ones I used to lube on my first car – a ’67 Ford Mustang. The preload setting on the old Ford however was a simple process of tightening the castle axle nut and then backing it off a quarter turn, and installing a cotter pin through the castle nut.

I learned from Mr. Asherman that the taper bearings on my R100RS are so over designed for this application, that I probably didn’t need to be much more scientific to get this job done and still get good service life from new bearings.  But I couldn’t resist doing the preload adjustment to the specification of 15 to 30 newton-centimeters. (about 21 to 42 ounce-inchs)

In a nutshell, adjusting the taper bearing preload on my motorcycles wheels was a simple matter of selecting the proper size spacer (referred to as the “wedding band” spacer) that controls the space available between the inner and outer bearings’ races once the axle nut is tightened.

There are two tricks involved with measuring the bearing preload. First spacers must be used to allow tightening the axle nut while the wheel is not installed on the bike.  I elected to use one of the suggested methods – I bought a dozen “top hat” spacers employed on the axles that could be stacked along the axle to take up the necessary space.  This might have been more expensive than one of the other suggested methods such as cutting a tube to length.  But the “top hat” spacers were cheap enough – and super easy to use.

The second trick is to measure the torque required to rotate the axle after the wheel was assembled with new bearings and spacers and the axle nut properly torqued.  Both Asherman and Fleischer advocated different methods – and I came upon a third after searching YouTube for videos about setting taper bearing preload.

My method was to use a dial torque meter.  I was able to find a used one on eBay for under $100.  The Snap-On TQS-025 is scaled in inch-ounce from 0 to 48 – perfect for this job.  It’s 1/4″ drive allowed me to attach a socket to fit the axle nut, and rotate the axle to take the torque measurement.  The “tell-tale” on the TQS-025 recorded the maximum torque registered while rotating the axle.

snap-on-tqss-025-fu

snap-on-tqs-025-dial

This video shows how I used the TQS-025 to measure preload – indicating 26 Inch-Ounces. Note the stack of “top hat” spacers to allow tightening the axle nut.

 

I also tried a different tool – a Proto 6104, a torque limiting screwdriver.  This tool allows setting a maximum torque on the inch-ounce scale (0 to 100) using a setting similar to a “clicking style” torque wrench.  This tool can be used to bracket the torque of the axle by choosing settings lower and higher than the actual preload torque.

proto-6104

The Proto 6104 was a little more expensive than the Snap-On TQS-025, and less precise in measuring preload torque.  But it probably has more useful applications in the workshop – specifically not allowing drive shaft filler plugs to be over-torqued.

This video shows the Proto 6104 set to 22 inch-ounce and not rotating the axle because the preload exceeds that torque value.  Note the stack of “top hat” spacers used as a single spacer to allow tightening of the axle nut:

This video shows the Proto 6104 set to 24 inch-ounce and rotating the axle – indicating that the bearing preload is less than this value:

These two tests allow “bracketing” to test the preload of the taper bearings.

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