steering bearing mod

 

 

Change to tapered roller bearings on your Earles Fork BMW motorcycle

Proper adjustment of the steering bearings.

by Duane Ausherman

This page is about the BMW motorcycle models R26, R27, R50, R60, R69, R50/2, R60/2, R50S, R69S.Earles forks, often called leading link suspension, were introduced on BMWs in 1955.  They were specifically designed for use on a bike with a sidecar.  They are known for providing a soft ride and being extremely robust.

BMW used ball bearings on the Earles forks and while they worked, they easily became notched with small detents in the straight ahead position.  In 1970 BMW changed to tapered roller bearings and they provided a longer life.  Neither set up is ideal for this application, but sort of works out OK.  The problem is that forks don’t make full revolutions.  They sort of go back and forth over a small range.  This means that the pounding that they get from the road is mostly in one spot.

The test for “notched bearings” can be done in several ways.  One of the first symptoms noticed by a rider is the inability to place the front tire exactly where the rider would want.  If a quarter were placed on the road, the rider couldn’t quite run over it.  Another symptom is to look at a track made by a bike on wet pavement at 25-30 mph.  If the track is a big S curve and not straight, then the bearings are probably notched.  Put the bike on the center stand.  Very gently swing the handle bars back and forth through center.  A notch can be easily felt.  In really bad cases the forks can be moved off center slightly and they will return on their own to the center.

Since you must remove the whole front end to replace them anyway, why not use better bearings?  The later style tapered bearings can be installed.  Do not go out and buy /5 tapered bearings for the steering.  They are quite close, but not the same.  I don’t know the relative cost, but compared to the labor it isn’t significant.  A properly lubricated and adjusted set of tapered bearings will last several times longer than the original ball bearings.  I understand that they can be purchased from Vech.

This isn’t a recipe type page, but if you are at all mechanical this is an easy job.  BMW usually, but not always, routed the wiring harness over the top casting part of the Earles forks in most cases.  That causes the harness to constantly rub and wear through it quickly.  I preferred to route it under that casting and get more years out of it.  If it is under then one must unwire the harness in the headlight before dropping the forks.  Make a drawing with colors of the wires and the terminal post numbers etc.  Aside from the wiring, an experienced mechanic can do the whole job in less than two hours.

Steering7.jpg (49332 bytes)

This is a harness after “surgery” to repair the damaged area.  The harness was fairly new, as it was supple and of the replacement type, not the original style.  I hope to write about that later, but it only affects the horn wiring.  We unwired the harness from the headlight and cut out the worn places and repaired a few other “altered” places in it.  This only took about two hours and was faster, easier and much cheaper than replacing the whole thing.

If for some reason you are using this page to start some other fork work and are going to try to reuse the steering bearings, put a clean surface down so that you can find the 54 balls after they fall all over the floor.  No matter what type of bearing you are installing for the steering, they should be over tightened a bit and then the adjustment backed off to normal.  This will help to fully “seat” the bearings.

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This is what the old race looks like when it is slightly lifted off of the casting.  This is the lower set of races.

Steering2.jpg (24391 bytes)

This is what the top race of the upper set look like in its dust cover.

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This is what it looks like after you have installed the tapered bearing to the casting.

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This is the tapered bearing mounted inside of the dust cover.

/2 BMW motorcycle steering bearing adjustment

This adjustment sequence is the same for the original ball bearings or the tapered roller bearing modification.  This procedure doesn’t apply to the telescopic forks but click here for what we call the “US” models.  The original BMW motorcycle tool kit comes with a thin flat combination end wrench to loosen and tighten the lock nut and make the steering bearing adjustment.

Steering6.jpg (27605 bytes)

This wrench has been modified to also work on the US models without removing the handlebars to make adjustments to the steering bearings.

Make sure that you have the washer mounted under the top plate.  Sometimes a PO has lost the washer and may not be aware of its existence.  Without the washer in place, the top plate will be warped downwards and eventually take a permanent set.

I wrote this to show how to do the adjustment. To do the adjustment assumes that all is in order, but at this late date, that could well be wrong. Thanks to Vech and another person, I have decided to start over. Some is a direct quote from Vech.

When you are doing any work on your Earles fork bike steering system, I suggest taking a very good look at it. At this late date, any of many things could be amiss and you might not realize it. This aspect of this issue might well bring more questions and that is OK. I will try to answer good questions by editing this article and that way others may profit.

Check your top plate for being flat, if not, fix it. A press works well for this fix because that plate is thick and requires some serious pressure.  Do you have the washer under it? You may have no washer, or the wrong one. They are provided in 4 thicknesses and Vech stocks them.

31 41 1 231 201—-steering head shim 1.5mm twins & singles 1955-1969
31 41 1 231 202—-steering head shim 2.0mm twins & singles 1955-1969
31 41 1 231 203—-steering head shim 2.5mm twins & singles 1955-1969
31 41 1 231 204—-steering head shim 3.0 mm twins & singles 1955-1969

  1. Tighten the lower steering stem nut TOO TIGHT initially, to ensure the upper and lower bearing races are actually seated all the way in the frame.
  2. Back the lower steering stem nut until one has a light drag on the front end.
  3. Temporarily Install the upper plate without the shim washer and upper steering stem nut. Mount the plate with the two bolts, just to hold it in place while you try to shove a washer, or shims, into the gap.  With the upper plate seated then take the existing washer, if you have it, and try to stick the edge of it between the upper plate and the lower steering stem nut. See if the shim washer is too thick, too thin, or just about right. If it is the proper thickness, take the upper plate off and install it. If it is not the proper thickness, measure the thickness, and referring to the above part numbers, order the correct one.  The gap can easily be measured with feeler gauges. Once you have a washer of the correct thickness, put a slight amount of grease on each side. This allows the lower steering stem nut to move easily for proper adjustment. 

I will give the (incorrect in my opinion) factory procedure for adjustment. It is to loosen the lock nut. It is on top of the thick plate that I will call the plate. Then use the wrench open end to get in under the plate to turn the adjustment nut. This is best done by two people. One gently pulling on the forks to feel the play. The second adjusting the nut at the same time. When you are happy with the adjustment, tighten the lock nut that is on top of the plate.

Sorry, but this doesn’t really work and here is why. If you had the forks off of the bike and only the lower steering stem nut screwed (adjuster) down on the threads of the steering stem, you would find that the adjuster has a bit of up and down play. These are fine threads and good quality, but still, there is a bit of play.

During your adjusting, the pressure from the bearings has the adjuster in the “up” part of the play. When the lock nut is tightened up, the adjuster is forced into the “down” part of the play. While this amount of movement is very small, it actually increases the tightness of the steering bearings. They will wear out faster and the evidence will be a “notch” as mentioned above.

Here is the solution that was used in my shop. Get the adjustment close. Tighten the lock nut down most of the way toward the final result. This puts pressure on the adjuster to move it into the “down” part of the play. Insert the wrench to do the adjusting as your helper gently pulls and releases the fork. You may need to tap on the wrench to move the adjuster. You may need to make several attempts of slightly too loose, or to too tight. After several times of going back and forth, you should get the “feel” of the right position. This “feel” is quite subtle to some people and obvious to others.  You must judge yourself before doing this task.  Now add a bit of torque to the lock nut. You are done.

Warning

 

Use grease liberally on the bearings.  Never let a car wash pressure wand get near these bearings, the wheel bearings or the swing arm bearings.  The hot soapy water, under pressure, will wash the grease out and ruin the bearings.  Water is the most common cause of wheel and swing arm bearings to fail.  Steering bearings fail from both water and/or improper adjustment.  It is common for the steering bearings to loosen up after a few hundred miles.  We always asked the customer to bring the bike back in 500 miles for a free check and adjustment.

Photos generously provided by Dale Thomas, thanks.