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Add tapered roller bearings to your Earles Fork BMW motorcycle |
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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. 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.
This is a harness after "surgery" to repair the worn through place. 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 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.
This is what the old race looks like when it is slightly lifted off of the casting. This is the lower set of races.
This is what the top race of the upper set look like in it's dust cover.
This is what it looks like after you have installed the tapered bearing to the casting.
This is the tapered bearing mounted inside of the dust cover.
This is what the whole "stack" of parts look like. The large round bushing thing that is in between the bearings is just to "represent the frame" of the bike. It is not real and you don't need one. The frame holds the cups apart when all is assembled. /2 BMW motorcycle steering bearing adjustmentThis 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.
This wrench has been modified to also work on the US models without removing the handlebars to make adjustments to the steering bearings. Sometimes this wrench needs to be "encouraged" a bit with a plastic hammer to loosen the lock nut. Tighten the adjuster just enough so that the free play goes away. I like to just gently pull on the forks to feel that slack or play. Don't give the adjuster any more than the amount that just takes away the play. The movements are very slight, or on the order of only a few degrees at a time. When you tighten up the lock nut on top of the plate, that will apply some additional pressure or preload to the bearings. Make sure that you have the washer mounted under the top plate. Sometimes a PO has lost the washer and one 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. WarningUse 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 for 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. |
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This page was last edited:
04/07/2006 - copyright
Duane Ausherman |
