Frequently asked questions

FAQ is a standard service with any serious website, so from now on with www. flyingbrick .de too. We do have a forum to discuss, among others, technical questions, but some of these are showing up frequently. The answers come from different sources, like the forum,, and are supplied without any guarantee to be correct or complete. Their shortness is intentional, they are not supposed to replace either workshop manual or a workshop visit. Corrections and additions to be sent to the webmaster as usual.

That is correct – at least in our latitudes. Lead was added out of two reasons:  First to insure a certain octane level, second as wear protection for the highly stressed valve seats. As a knock protection it is not necessary anymore, The 98 octane of  the former premium fuel are also standard for the current premium – Shell’s sulfur- free „V- Power“- fuel is said to have 100 octane.  Wear protection by residues of soft lead on the seats is nowadays offered by lead ’substitutes’ like Castrol TBE., available in 250ml- flasks at bigger gas stations. An EUR 6,00–flask  lasts for 250 l gasoline, i.e. in the case of the K100 4000- 5000 kilometers. After refueling lead substitute is added according to the amount of gas, measuring made simple by a dosing device contained in the top; the flask fits easily into the rear seat compartment. Modern lead substitutes are apt to catalyser use and also clean valves from redidues.

This is normal and caused by the horizontal mounting princple of the engine. Small amounts of oil pass by the piston rings into the combustion chamber. Modifications were carried out in later models, but the problem is of minor matter and no defect.

Possibly the fuel cut-off does not work properly. .On the engine’s left side above the valve cover you find the Injection system with the throttle mecanism. At the right end of the throttle shaft there is a small black box, the cut-off switch. Turning the twist grip (engine turned off) it should  click slightly; if it doesn’t, the switch is not working and does not cut off the fuel supply. In this case the switch must be calibrated by turning the lever on the shaft,( loosening the yellow marked screw). Further possible reasons are leaks at the valves and the exhaust system

Often the reasons are faulty HT- leads. Unfortunately this cannot  be checked visually. Advisable is a change, the spark plugs should be changed as well. Many  BMW- riders say the K- series will run satisfactorily only on Bosch spark plugs and advise against using other brands like NGK. With EUR 25 per set  however,l the plugs are comparably expensive. Poor starting behaviour also could stem from a faulty fuel filter, causing fuel splashing around in the tank during starting, furthermore the reasons are many and go from no fuel to lacking compression.

According to experiences of K- owners there is less wear on the timing chain itself than on the cam chain guidings and the hydraulic chain tensioner, the latter showing a worn rubber pad, the former announcing a faulty tensioner by a loud rattle immediately after starting. After a short period the noises cease. As the tensioner is normally operated by engine oil pressure, a ratched mecanism prevents the chain to run loose just after starting. If this mecanism fails, by all means the tensioner must be changed. For this purpose the valve cover must be removed  and the crankshaft cover loosened and pulled sideways. Thereafter the timing chain cover may be removed without draining the cooling fluid.

Clutch adjustment is different from most bikes: first you free the clutch cable from the operating lever; then you adjust the protruding length from nippel to outer cable to 75 millimeters by turning the adjusting screw of the handlebar lever and fit the cable again. Now you loosen the adjusting bolt on the operating lever one to two turns , turn it back in just until you feel resistance and secure it with the counter nut. By the way the Teflon cables of the K’s must not be greased or oiled to avoid sticking by expansion of the coating.

Particularly on older models there are found cracks or missing bolts.  1988 the fixation of the part was modified, which does not help much the owners of older bikes. Generally a tension-free mounting should be observed. The front one of the five bolts is fitted with a silentbloc, so you should grab it from the rear with an open spanner.

It sounds sad: this lack of  torque is a result of the 100 hp-engine design. As tests show, there is no improvement to be realized neither by chiptuning, nor changing airfilters, for example K&N. Cold comfort: two-valves have an agreeable buildup of torque , four-valves the higher output. After all, the nominal torque of the four-valves is higher but less even with a `'peaky' power curve, the diagram to be seen here.

Thats a well known phenomenon especially with models up to 1988. Furtheron the supplier Motometer  fitted housings with Gore-Tex- membranes( two round holes underneath). Reasons for the problem are obviously air temperature differences in- and outside, caused by the instrument lighting; there is no efficient remedy available.

Probably the push-in- connectors inside the unit are oxidised or loose. The instruments should be taken out and the connectors be cleaned with a contact spray moisted Q-tip. No spraying directly to the instruments! Taking advantage of the instrument unit  being dismantled, it pays to change the bulbs too. The reason for a faulty gear indicator could also be a bad gear switch; to change this switch the swingarm has to be removed.

This lamp controls the rear pilot and brake lights and their respective switches and lights up, when one of these components fail. After switching on the ignition the rear pilot light is checked automatically,for the remaining components front and rear breake have to be actuated;  with everything OK, the lamp is switched off. Consequently a failing bulb in the rear is indicated immediately, a failing switch only with the next start up.

On ABS equipped bikes the lamps functions in combination with the ABS- light inside the instrument. Switching on the ignition, it lights steady, the ABS-light blinks. With the rear pilot light beeing OK, and applying the brakes, rear brake light is also OK, both lamps blink. Only when the bike rolls with a speed of at least 4 km/h, ABS now being able to check the wheel sensors, both lamps go out at the same time. The ABS- system requires nominal voltage;  with a faulty or discharged battery the lamps will keep blinking during riding. ABS- wheel sensors must have the correct clearance to the toothed segment rings. On the floating disk-front brake of four valve models (lateral teeth) it is 0,50 - 0,55mm, any other fixed disk equipped front and rear brakes (radial teeth) it is 0,60 - 0,65mm. A feeler gauge to check the clearance can be found in the tool set. Adjusting is done by inserting spezial distance pieces between the sensor and ist mounting.

There may be a contact problem too(see above). In any case the clock may be changed completely, as it has a sliding fit in the instrument unit. No repair possible, price is about EUR 95.

Yes, on all K 75 and 1100 plus the K 100- models from 1986 onwards featuring a float within the fuel tank, which is necessary for control. These models have just one five Liters- warning lamp inside the speedometer. The optional set with clock and water-thermometer is from EUR 178,45 to 203,50. With the earlier K 100- models  with two warning lamps (4 Liters/7 Liters)  updating would be to expensive. In the US however a “Fuelplus” module is available to convert the digital clock of all K- models into an on-board computer.

Probably poor earth contact, to be fixed with an additional lead from the gearbox earth point to the frame earth point on the upper frame tube.

Apart from the respective component being faulty,  loose or oxidized push in- connectors should be checked for. It makes sense with an older bike while doing maintenance or cleaning, to take apart all push in- connectors, clean them with contact spray ( connecting /disconnecting them several times) and preserve them with battery grease. Another reason for trouble is the ignition switch with frequently corroded contacts, to be cleaned and preserved in the same manner.

Mostly the BMW- dealer can find in his documentation only the complete brake cylinder for more than EUR 200. There are however service kits for sale; via the BMW- sparepart number the supplyer MAGURA can give information if necessary. The service kit consists of piston and seal and costs EUR 35,09. The sparepart- number is 32 72 2 332 037. In earlier spareparts- lists the number does not figure. In 1998 the cylinder, which tended to corrode, was replaced by an anodized one. BMW states that the service kit is to be used only with the later version

In the forum a whole bunch of measures have been discussed. Suspicious in the first place are the tires.The formerly popular set Metzeler ME33 / ME99A , especially in nearly worn down condition is prone to unstable behaviour. A better combination is ME 33 / ME 55 A. The latter does not have a center groove like the ME 99 A which seems to reduce sensivity. Best bet of the forumistas is the Bridgestone BT 45. As further reasons the suspension elements are mentioned: on the front a change to progrssive fork springs (f.e. Wirth or Technoflex)and new elements on the rear. With the later K 100 RS and K 1100 – stiffer frame and wider tires – the chassis stability problems have ceased.

Any BMW- dealer can order these documents (they are reprinted when necessary). There are workshop manuals from Bucheli, Delius Clasing or Haynes, available in the bookshops or with Amazon. A list of available books you`ll find here. For K1 and K 100RS 16V there are no printed manuals for sale, neither from BMW nor other editors. At least BMW provides a microfiche for EUR 7,12 with the number 01 50 9 798 850, perhaps a copy shop will make a blueprint for you.

BMW supplies either finished keys or key slugs. On the other hand it is possible to order ignition switches for a certain key. There should be established before, if a complete set is cheaper. The folding key can be ordered with lighting. A finished key you get for  EUR 21,23 under the number 51 21 2 315 252, the key slug is only EUR 3,00 less.

No, not with the K models. This was only the case with earlier opposed twin- models.

To be looked after in „Types / Frame numbers“, including infos on frame and engine numbers.

Translation by Peter Zettelmeyer