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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R100GS MotoMacondo ProTaper Handlebar Mounts

Funny how an injury increases your ergonomic awareness. A scaphoid fracture in my left wrist, and the following surgery to insert a titanium screw, left that hand weak, sore and unable to stand the normal rigors imposed by the standard GS bars. I’d known Ricardo Kuhn was making adaptor mounts so BMW GS riders could use Answer ProTaper handlebars, but I didn’t know that Ricky started making these mounts because he wasn’t happy with the factory riding position, either.

In addition to accommodating the large bulge in the middle of the ProTaper handlebars, Ricky’s bar clamps move the bars both up and back, making stand up riding as well as sitting riding much easier. The ProTaper bars have less “sweep” than the BMW bars, and the result is less kinking of the wrist joint. And the aluminum material also damps out more vibration for clearer mirrors and less fatigue.

Fitting the clamps and bars is very straight forward.

Start by removing your fuel tank (you really don’t have to do this, but it does remove the danger of scratching or denting the tank). Then remove the zip ties that bind your control cables and wires to the old bars, and take off the grips. I like to use compressed air to help slide the grips off, and use a duster attachment to force air between the grip and bar while I twist and pull. Once the grip breaks loose (a philips screwdriver between grip and bar helps here) the grip will slide right off. With the bars clear, pop out the four bolts that hold them in place and set the bar and clamps aside.

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Magura X-line Handlebars

The old power line road was generally in good shape, at least it was between the arroyos. When the road dipped into the washed out beds of the dry creeks the gravel got pretty loose and deep. When the road dropped into the creek bed itself, there wasn’t much else to do but stand on the pegs and stay on the gas. Sometimes that went on for quite a while, and my lower back started to remind me just how far out of shape I was. It didn’t help that the Answer Hyperlite bars I’d installed with Ricky’s risers were a good inch and a half lower than the stock GS bars. I was pretty happy with the standing position on the newer R1200GS, and wondered if a taller aftermarket bar would help on the R100GS. With Answer, Moose Racing, and Renthal the most rise I found was about 150mm. BMW’s R100GS bars have about 200mm of rise, which is comparable to the new R1200GS bars. Santa Cruz County BMW offered a bar through Wunderlich that was a match for the one on the 1200, but at almost two hundred bucks it was a bit too much for my budget.

The GS mailing list came to the rescue with a post asserting that Magura was the OEM for the 1200GS bars, and that the same bend was available in their “X-line” model. I downloaded the catalog from the Magura web site, but found no reference to the taller bar. I found a link to the Magura USA web site, but again no specs for the bars. But there was an email address for tech support, and a brief note was quickly answered by Jeff Enlow providing not only dimensions, but a Magura part number for the bar:

Width – 778mm
Center Width- 104mm
Grip Length- 201mm
Rise – 198mm
Pull Back (Sweep) – 92
Part Number – 722120

A quick call to my buddy Mike at Fremont Cycle Salvage and he had a pair on the way from Parts Unlimited.

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R100GS Handlebar Risers

Hey, ever tried standing up on the pegs of a factory GS? Notice how you’re all bent over, and it’s difficult to keep your weight from pulling on the bars. That makes the bike wander because you aren’t letting the bike move freely under you. Well, these handlebar risers aren’t the whole solution, but they’re a lot of help. They move the bars up and back by about an inch, which may not seem like much but is fairly significant ergonomically. The pair shown here is made from some aluminum bar stock I had laying around, but there are commercially available risers if you don’t want to make your own.

The drawing at right is pretty self explanatory, so I’ll just make a few comments about the machining sequence. I started with a block about 2.5″ x 3″, and the first thing I did was mount it in a four jaw chuck, center it, and drill and bore the .875 hole for the bars. That let me get a very smooth hole of exactly the right diameter. I then used the milling attachment to square the ends and sides, and to drill the bolt holes. The last thing I did was split the block through the handlebar hole, and then square up the saw cut ends.

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R100GS Handguards & Heated Grips

Back in my dirt bike days it didn’t take many busted clutch levers and throttle housings before I realized that the ends of your handlebars aren’t a very safe place for delicate components. Pawing through the scrap box one day I ran across about three feet of 1/4″ by 1″ aluminum bar, and hit upon the idea of bending up some gards that would keep rocks and tree limbs from doing any damage to the parts behind them. Never broke another lever after that. The same idea started running through my head shortly before a winter run to Death Valley that held the promise of snow riding and its accompanying get offs.

This time, though, I wanted to preserve the functionality of wind deflection that the flimsy BMW hand protectors provided. Acerbis makes several styles of guards, but only one offered the aluminum bar reinforcement of my old bark busters. Touratech sells a slightly modified version touted to be especially designed for the GS, but at the usual outrageous price. A few minutes eye balling the standard Acerbis offering at nearby Fremont Cycle Salvage had me convinced I could make them fit, and even get them working with BMW’s electric grips. All it would take is a little lathe time and some patience.

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R100GS Flip-A-Lever Throttle Lock

BMW has a complete line of accessories for motorcycles destined for police use, and one of the handier of these is a friction throttle lock. The idea is simple: It screws into the throttle grip housing and rubs on the flange of the grip to resist the pull from the carburetor butterfly valve return springs. Screw it in tight enough and you can take your hand off the grip and the bike will keep running at the same speed. Back it off a bit and the weight of your hand will have the same effect, and it will be easier to change throttle openings to compensate for hills and such. Most useful on long trips to let your hand take a break once in a while, it’s also nice to be able to take your hand off the throttle to adjust your face shield, open a vent in your jacket, or wave to someone at the side of the road.

This little doodad has been around for years, for most of BMW’s motorcycle line (the K1200 series is a notable exception).

Simple as it was, the BMW screw took some fumbling with to get set just right, and if you wanted to change it you had to take your hand off the grip and reach under the bar to make the adjustment. Usually this resulted in the bike lurching down to full closed throttle as the grip snapped shut. At least it did until Bill Schneider got to thinking about a better way. The result of his thought experiment is pictured above.

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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

Hedz:

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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