Throttle & Clutch Cables

In my shop I saw many control cable failures from these things.

1. Throttle cables on the Airheads: Left cable failing at the carburetor, due to the throttle cable being bent as owners checked the oil dipstick. Do not bend the throttle cable at the left carburetor when checking your oil. There is no need for the oil dipstick to be overly-tightened. Bending the left throttle cable is a prime cause for that left cable to have increased friction, possibly spread some coils on the wrapped sheath (& making that carburetor difficult to synchronize, if bad enough), & eventually you might break an inner strand …usually where you can see it between the throttle lever on the carburetor, & the sheath. A single strand found broken (You do inspect these cables regularly, don’t you?), will usually cause other strands to eventually break from the same reason why the first strand broke ….this will …or can …result in total cable failure in as little as few hundred miles or so.

2. The bushing at the clutch lever at the handlebars is a replaceable plastic part and as it wears the result is the lever can move up and down & also allow angular motion. If worn enough, the stranded core of the cable will start rubbing, or even catching, on the sharp edged guiding slot in the lever. Eventually a strand breaks, failure comes soon as more strands break. The bushings are easy to replace and not expensive. If your new bushing does not finger press into place, heat the lever first. The Nylon-like bushing is 32-72-1-232-662 and has been used from 1976 onwards. That bushing may need light reaming for a good fit to the pin. If you do not have a 8 mm tapered ream, you can use very carefully selected drill bits, to progressively remove a quite small amount of material, a few thousandths at a time …until the pin fits properly …an easy, but not loose, push-sliding fit. The lever has a recess, and in that recess must be a waverly washer, 32-72-1-230-871. I recommend the sharp edge of the slot in the clutch lever be filed smooth. Be sure the crimped end of the cable that fits into the clutch lever at the handlebars is not fouling the lever.

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Lubing Steering Head Bearings

Cleaning and lubrication of the steering head bearings should be done at a scheduled mileage/time but most let it go until the steering has a ‘notch’ felt in the straight ahead position. This procedure was developed specifically for a 1983/1984 R100RT, but is similar for all Airheads. I advise you to read this procedure through before beginning. Cleaning and regreasing MAY WELL eliminate “notchy-ness” that SEEMS to indicate need for new bearings and outer races. It is best, but not mandatory, to do this procedure after installing new balanced tires, as road crown and tire squaring wear, and balance, might have an adverse effect on trying to make final on-the-road adjustments. This is not hardly just for the front tire….most riders do not know that a squared-off REAR tire is THE most common cause of wobble and weaving from the tires. The author has usually, but not always, done this procedure to his own bikes after installation of a new front tire, but when the wheel is off the motorcycle. If your REAR tire is not squared-off considerably, it will be OK for the final procedure, which are riding tests to get the preload adjustment ‘just right’.  It is possible to do this procedure with the front wheel in place, usually that means having the front wheel hanging over the edge of a curb, or the centerstand is in use and on a piece of wood, so the front end can be dropped a couple of inches.

Cleaning and lubrication of steering bearings is not at all difficult, but if a bearing is found truly bad, replacing them is more labor intensive, as part of any fairing must be removed, and possibly brake piping, cables, etc. Contrary to some popular belief, our BMW steering head bearings of the tapered ‘Timken’ style may well last over 200,000 miles. If the bearings/races/shells are in good condition and properly greased and adjusted, the steering will be light, smooth, without any straight ahead notch. You likely will not find out if the bearings are really bad, that is, in need of replacement, UNTIL you first try cleaning and greasing.  In a SHOP situation, the bearings are not cleaned and lubricated and then adjusted to see if any notch is gone. In a SHOP situation, labor is too costly for that.  A shop can not take the time to clean and regrease, and then find out that the bearings really are bad, so a shop always replaces a notchy bearing.  YOU, on the other hand, don’t need to do that…..and will often save a LOT of money, and a considerable amount of labor saving is possible.

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Discussion of Tank Slappers


The past several days on this topic has resulted in a host of opinions ranging from almost agreement to diametric opposition. It needs some clarification. There is a lot of flesh at stake… The causes and cures have been published in AIRMAIL tech pages more than once and many years ago in BMW News in the late 1970’s in feature articles on the subject. But for you neophytes and latecomers here it is in a nutshell……

First and foremost, never let the problem manifest into a worsening condition. The progress from normal handling to dangerous deterioration is usually slow. Don’t ignore the warning signs and get it fixed before it fixes you so nobody can fix you. You will usually get some early warning signs before the big event of the tank slapper happens.
The tank slapper is of course the worse, almost always preceeded in miles and time with a lesser degree wobble mishandling. Weaving is an entirely separate phenomenon.( discussion forthcoming)….
The most dangerous combination for the wobbling and tank slapper is a handlebar mounted wind screen arrangement, a solo lightweight rider, a significant load at the rear of the machine rear of the rear axle, diagonal headwinds, and of course, steering head bearings too loose or worn and notched. The more of these ingredients in the act, the greater the chance of disaster-and the event may happen without warning.

The primary instigation of wobble is a physical resonance set up in the frame and steering geometry that once starts, feeds the accumulated resonant energy back into itself to accentuate the problem. This is what makes it so difficult to squelch once commenced. A rigid frame and steering coupling (tight steering head preload) will avoid the resonance,by absorbing the energy needed to create and manifest the problem, but a small amount of liberty in movement of the steering is needed for continuous self correction of tracking versus road aberrations as the machine moves along. The proper preloading of the bearings is a compromise-to allow enough movement for corrective needs and not so much as to allow resonance to initiate. Kind of a tightrope act.

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Discussion of ‘Tank Slappers’–Part 1

Discussion of Tank Slappers–Part 1 (Snowbum) Since the original publishing of the discussion about tank slappers”, I finished writing an extensive article on that and allied subjects.  This was after accumulating a very large number of tests on a large number of BMW Airheads, mine, and customer’s bikes.  The article is on my website. Here […]

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