Author Topic: I just bought a 2 valve K bike - what should I know? (Now available in PDF!)  (Read 42822 times)

Offline frankenduck

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This will be an evolutionary thread.  I will update it as needed.  If you have any recommendations on stuff to add or change then just post in this thread and I'll update this original post as appropriate.


This post covers operation of 2 valve K bikes.  This includes the following K bike models:

K75, K75C (and US-only K75T), K75S, K75RT
K100, K100RS(up to 1990), K100RT, K100LT

***********************************************************
UPDATE ADDED ON 1/8/12:  I can't believe I forgot to include this when I first did this write-up:

There's a number of people out there who consider the K75 to be a "slow" or "underpowered" motorcycle.  Well, it is and it isn't.  It certainly won't beat a Hayabusa off of the line but if you know how to take advantage of the K75's (or K100's for that matter) power curve then you can get a lot more oomph and fun out of it than a lot of people think.  The key is to "wring the snot out of it" by keeping the engine above 4,000 RPM and riding it through turns in a gear or two lower than you "think" you should.  This will give you a lot more torque for engine control entering and, more importantly, exiting turns.

Do not worry that you're abusing the engine.  K bike engines are "bulletproof" and can literally run all day long at 7,000 rpm without skipping a beat. (I know, I've done it.) They don't even redline until about 8,500 RPM.  It's not a Toyota Camry, don't ride it like one.

And don't be afraid to use third gear for passing.

Ride it like you stole it...  REALLY!

(Insert disclaimers about riding within your skill level, taking it to the track and other such stuff here.)
***********************************************************




If you're looking for general maintenance information then click here.


IGNITION SWITCH:  The ignition switch has three positions. I'll call them left, middle and right.

Left: Everything off.

Middle: Headlight's parking light and tail light on.  The key can be removed from the ignition switch in the middle position so be sure to turn the key all of the way off before pulling the key out and walking away.

Right: This is the on position for starting and running the bike.  The key cannot be removed in this position.


STARTING THE BIKE:  The bike must be in neutral (as indicated by a zero in the gear display in the tachometer face plate and the neutral light being illuminated) or the clutch lever must be pulled in.  The red kill switch on the right hand combination switch must be pointing straight up.  Push the green button on the right hand combination switch to engage the starter.

If you try to start a K bike with a low battery then there's a chance that the starter relay will only partially engage which creates a spark that can arc and weld the starter relay contacts together.  If this happens then the starter will keep going (and going, and going...) even after you release the starter button.  The quickest way to disconnect the battery in the event of this occurring is to disconnect the battery ground cable from the left side of the transmission.  If you think this might happen then it's a good idea to check that bolt ahead of time as many times that bolt was last touched when the bike left the factory and some corrosion may have built up in the threads.

In general, K bikes don't need a lot of gas to get started.  Before starting it, I've always found that a quick flip of the throttle and putting the choke lever to the first position will have the bike start right up. (It's a fuel injected engine so technically it's a throttle advance, not a real choke, but BMW labeled it a choke so that's what people call it.)

There's no need to let the engine warm up.  BMW recommends just starting it up and riding off.  It'll be a little cold-blooded for the first couple of miles so leave the choke on for the first few miles. On 1990 and earlier bikes, the yellow indicator light in the tach face plate will be illuminated to remind you that the choke is on. For whatever reason, BMW stopped installing the switch for this in 91 and later bikes so if you've got one of the later bikes it's not broken, it's just not there. (It is possible to retrofit a switch to the throttle body assembly if you really care about the choke light. All the wiring is there in the main wiring harness and the instrument cluster.)


SHIFTING: K bikes employ the typical one down, four up shift pattern common to most motorcycles. Some people think K bike transmissions are clunky.  In my experience it really varies from bike to bike. 

One thing is for sure though, K bikes don't like timid shifts and will leave you in a "false neutral" if you don't shift assertively.  This doesn't mean that you have to stomp on the shift lever, just pull in the clutch and shift with authority.

Some people subscribe to a "preload the shift lever" theory (put some pressure on the shift lever prior to pulling the clutch in) but I've owned quite a few of these bikes and have never found that to be necessary on any of them.


HANDLEBAR CONTROLS:

The throttle, front brake lever and clutch lever function pretty much as you'd expect them to.  One thing that a 2 valve K bike might have installed is a throttle friction screw which can be used as a poor man's cruise control.  It's located on the underside of the throttle perch, can usually be turned by hand and looks like this:

TURN SIGNALS: The turn signals are the paddle type switches at the bottom of the left and right combination switches.  If you're coming from another brand of bike then you might think it's goofy at first but it doesn't take that long to get used to it.  The button with the "X" on it on the right combination switch cancels either turn signal.  Push that button up with your right thumb to cancel either turn signal.

K bikes also have an automatic turn signal canceling function that turns off the turn signals after traveling approximately 210 meters.  (You can disable this by cutting the blue/green wire at the flasher relay.)

HORN: The horn switch is located on the bottom of the left hand combination switch.  Push this button up with your left thumb to sound the horn.

HEADLIGHT SWITCH: The headlight switch is the big yellow three position switch in the left combination switch.  The middle position is the headlight low beam.  The up position is the high beam.  The down position is a momentary swtich for the high beam.

(There's a square white one wire connector in the relay box under the gas tank. If it's connected then the low beam stays on with the high beam.  If it's disconnected then the low beam goes off when the high beam is on.)


DASH SWITCHES

HAZARD SWITCH:  This is the switch with the red graphic insert with a triangle on it.  Pushing it down turns on the four way emergency flashers.  The hazards can only be turned on when the bike is turned on.  However, they can be left on when the bike is turned off.  (I suspect BMW designed it that way so that some idiot couldn't come by and turn your flashers on and run down your battery when you're away.)

HEATED GRIP SWITCH: (If your bike is equipped with heated grips.) The graphic on the heated grip switch is a grip with a coil of wire around it.  It is a three position switch.  Pushing the top of it turns the heated grips on on the high setting.  Pushing the bottom of it turns the heated grips on on the low setting.  The middle position is off.

ABS SWITCH: (If your bike has ABS.)  The graphic on this switch is the letters "ABS" bracketed by a couple of brake shoes on a red background.  Hopefully you'll never need to use it.  If your ABS is in fault mode then the ABS lights in your instrument cluster will keep flashing when you're riding.  When this happens that means that your ABS is not operational and that you just have normal brakes.  When this happens pressing the ABS switch will make those lights go solid for about ten minutes so it's not as bothersome as the flashing lights.  The ABS warning lights will then start flashing again.  Hit the ABS switch again to make them solid for another ten minutes. (How to deal with a faulted ABS system is addressed elsewhere.)


BULB MONITOR UNIT: (a.k.a. "the triangle light")  In the center of the instrument cluster is a red indicator lamp with a triangle.  This light is controlled by a relay of sorts known as the bulb monitor unit, or BMU.  The BMU tests four things:

1) The front brake switch
2) The rear brake switch
3) The tail light running light bulb
4) The brake light bulb

When you first start the bike this light will remain on until you have activated both the front and rear brake switches. If it remains solid after you've applied both brakes then either one of your switches is not working or the tail or brake light bulb is out.  (On ABS equipped bikes, once the brakes have been applied, it will flash in conjunction with the ABS indicator at the bottom of the speedometer faceplate.)

If the BMU light comes on or starts to flicker while you're riding then either your tail or brake light is out or on it's way out.  Note that sometimes you may still have a functioning brake/tail light but either the contacts are getting dirty or the bulb's filament isn't working well enough to make the BMU happy.  Replacing the bulb with a new one should cure this.


TURN SIGNAL "HYPERFLASH":  If one of your turn signals is flashing at twice it's normal rate then the flasher relay is telling you that one of your turn signal bulbs is out.


ABS EQUIPPED BIKES:  If your bike is equipped with ABS then the ABS warning lights will flash until you've ridden several feet.  The reason for this is that the ABS control unit (a.k.a. ABS brain) tests all of the following components as part of it's initialization process: the front ABS sensor, the rear ABS sensor, the front ABS modulator, the rear ABS modulator and the brain itself.  The front and rear ABS sensors cannot be tested until the bike starts moving and the sensors send pulses to the ABS brain.

If the ABS warning lights in the instrument cluster continue flashing after you've started riding then this tells you that the ABS is not operational.  The bike is still safe and ridable though, you just have normal non-ABS braking.  As mentioned above, pressing the ABS dash switch will make the lights go solid for the next ten minutes so they aren't as obnxious as when they're flashing.


CLUTCH LEVER SIDE STAND RETRACTOR: Two valve K bikes have a mechanical side stand retractor that retracts the side stand when the clutch lever is pulled in.  It can be adjusted by turning the special nut on the rod down at the back of the transmission. (See #7 in the attached diagram below.)  If tightening it all the way doesn't adjust it enough then I've found that putting a bent washer inside the special nut can help.

It you're going to be parking your bike in an area with a lot of doofi (plural of doofus) around like near a bar, college campus or high school then I'd recommend putting the bike on the center stand.  What can happen is that some witless doofus will hop on your bike, stand it up and play with the controls.  When they pull in the clutch they'll unknowingly retract the side stand and then when they get off your bike they will promptly drop it on the left side.  When you get back to your bike it will have some nice damage on the left side and chances are they won't leave a note offering to pay for the damage they've caused.


PUTTING THE BIKE ON THE CENTER STAND: K bikes have a lifting handle along the left rear diagonal frame member.  It folds up and out and aids in putting the bike on the center stand.  Being rather heavy beasts it does take some effort and technique to get them up on the center stand.  Here's some pointers on how to make it easier:

1) Put the bike in neutral.  This allows the rear wheel to rotate freely and reduces the initial resistance to moving backwards.

2) Point the front wheel straight ahead.

3) Place your left hand on the left handlebar grip.

4) Pull out the center stand lifting handle your with your right hand.

5) Push down on the center stand with the ball of your right foot until the left "foot" of the center stand hits the ground.

6) Slowly rotate the bike to an upright position until the right "foot" of the center stand also touches the ground.

7) Using mostly downward pressure on the center stand with your right foot, pull the bike back and up onto the center stand.


GAS CAP The gas cap opens by insterting the ignition key and turning the key about 90 degrees counterclockwise.  When closing the gas cap it helps to give it a good rap with the butt of your hand to make sure that it latches completely.


SEAT/HELMET LOCK: For "normal" K bikes: (86 and later non-low seat models)  The seat/helmet lock is located about half way back of the seat on the left hand side.  The lock has three positions. I'll call them left, up and right. When the lock is in the left position (all of the way counterclockwise) then the seat lock is unlocked and can be opened by pushing in on the lock. When the lock slot is vertical and pointed straight up the seat is locked.  With the key inserted, the helmet lock is released by turning the key to the right (all of the way clockwise) and pushing in the lock. (As you'll soon discover the helmet lock is pretty darned worthless.  It can be made somewhat useful if you use a helmet lock extender.)

Make sure that the seat lock latches when you close the seat.  If you don't then the seat latch rod on the seat rides on top of the hook of the seat lock which will eventually wear it out and break it.  The length of the seat latch rod can be adjusted by loosening the lock nut at it's base.


ALTITUDE PLUG:  The fuel injection control unit by Bosch is named L-Jetronic.  It was designed in the early 80s and unlike most modern FI brains does not sense the ambient air pressure nor adjust the mixture for the reduced ambient air pressure found at higher altitudes.  Instead K75s and K100s have what's commonly referred to as an altitude plug.  When you go above 4,000 feet in altitude you insert the plug which tells the L-Jetronic to adjust the mixture.

The connector for the altitude plug can be found along the frame rail above the back of the throttle bodies.  The picture below shows the connector with the factory black protective cap installed.  Sometimes it's hidden behind the frame so you have to dig to find it.



The altitude plug is BMW part # 61 13 1 459 504.  All it is is a loop of wire that shorts two leads.  I usually wire it up to a dash switch because stopping to insert or remove a plug seems kind of dumb to me.

K BIKE ODDITIES

SMOKING ON STARTUP:  Any K bike, if left on the side stand long enough, will generate a good amount of smoke when you start it.  This is because when the bike is on the side stand the cylinder head is angled downward and oil seeps past the piston rings into the combustion chambers.  Aside from the smoke that it generates it's really not an issue.

This is especially true for model year 1988 and earlier K bikes.  The rings on the early bikes let more oil by and hence those bikes will generate a lot more smoke.  There are a couple of ways to minimize smokey startups.  The first is to use the center stand.  That way the engine is level and much less oil, if any, seeps past the rings.  The second method is to turn off the bike and tilt it to the right for about ten or fifteen seconds before putting it on the side stand.  This allows most of the oil behind the pistons to drain back into the sump so there's less to seep past the rings into the combustion chambers.


BOUNCY K75S INSTRUMENT CLUSTER: "They all do that."


K75 BACKFIRING: "They all do that."  If you're used to using moderate to heavy engine braking to slow down then a K75 will overfuel a bit and backfire.  At least for me, the more miles I put on my first K75 the less it backfired.  The bike kind of subconsciously taught me not to engine brake to the point where it would backfire.

K BIKE WHINING:  It's normal. It's the fuel pump working inside the gas tank.  As you get low on fuel it will tend to get louder as less of the fuel pump is submerged and the empty gas tank becomes a larger resonating chamber.  Since the fuel also serves as a coolant for the fuel pump it's a good idea not to run your tank extremely low on a consistent basis.  I usually refill when the low fuel idiot light in the instrument cluster illuminates.

"JACKING":  Given the design of the monolever shaft drive, 2 valve K bikes also experience a phenomenon commonly referred to as jacking or the shaft effect.  What the rider experiences when this occurs is feeling the rear end of the bike rising up or "being jacked" under heavy acceleration. This is inherent in the design and normal for 2 valve K bikes. It occurs due to the geometry of the monolever rear suspension setup.  What happens is that the application of a significant amount of force at the rear tire's contact patch causes the monolever swing arm to rotate downwards slightly and raise the rear end of the bike.  The crude diagram below might help you understand why this occurs.

The jacking effect is more noticeable on K100s than K75s since K100s have more torque/power.

SPEEDOMETER ACCURACY: K bike speedometers tend to run about 10% fast from the factory. You can calibrate the speedometer youself though.


***** ADDED 8/8/12 *****

ENGINE OIL CONSUMPTION: It is normal for K bikes to consume or "burn" oil.  Therefore it is a good idea to frequently check the oil level in the oil sight glass window on the lower right side of the engine on the oil sump. (See attached diagram.) The top of the circle in the oil sight window is the maximum oil level while the bottom of the window is the minimum level.

The rate of oil consumption seems to vary by individual bike but in my experience generally tends to be about a quart every 1500 to two thousand miles. The maximum oil consumption rate specified in the BMW service manual is 0.15 liters per 100 km (2.57 quarts per 1,000 miles) which seems insanely high to me.

CHECKING/TOPPING OFF THE OIL: Put the bike up on the center stand on a level surface.  Check the level in the oil sight glass window when the engine is cold or, if warm, allow several minutes after turning it off to allow oil in the engine to drain down into the sump.

Add engine oil in the filler hole at the right rear top of the crank case cover.  Add a little and then give it a few seconds to make it's way into the oil sump and then check the level again.  I generally fill it to about 2/3 to 3/4 level between the top and bottom of the the ring for local riding or, if I'm planning on going for a long ride (500+ miles), then I fill it to the top of the ring in the oil sight glass window. Check the oil level at least daily when out touring.
Once I had a Collie pup. Dug a hole and covered him up. Now I sit there by the hour. Waiting for a Collie-flower.
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Offline scbmwrider

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Re: I just bought a 2 valve K bike - what should I know?
« Reply #1 on: May 21, 2011, 07:18:57 AM »
Remember that your K bike is somewhere between 16 and 26 years old.  Check the rubber stuff that may have dried out and cracked.  Like the crank case breather hose and fuel lines.
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Greg Hunt      Moore, SC

93 K75S
84 R100RT

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Offline 177in70s

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Great details to help K bike owners.   My 85 K100RS goes up on the center stand pretty well:  Two hands on handlebar. Swing R leg off. R foot lowers center stand to touch ground, then I rock bike to get both sides of centerstand to touch down.  Grab lift handle with R hand, R foot on centerstand lever.  NOW catch right knee under right hand on handle, extend calf muscle, this lowers centerstand and lifts handle using my calf and not my back much.    Another tip: Buy adhesive backed "sandpaper" and stick 2" by 2" piece on center stand foot lever.  The stuff is made for slippery steps on Recreational Vehicles etc.  Another tip:  Grease the centerstand grease fittings every year or two, to swing up more easily.  In the bottom of my left rear case is a piece of 1/4 plywood jig sawed out to fit the bottom of the case, it also goes under the centerstand on softer ground.

Offline frankenduck

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Re: I just bought a 2 valve K bike - what should I know?
« Reply #3 on: January 08, 2012, 06:59:17 PM »
 bmp


For an update that I just added at the very top of this thread.
Once I had a Collie pup. Dug a hole and covered him up. Now I sit there by the hour. Waiting for a Collie-flower.
New to K bikes? Click here.
K Bike Maintenance & Mods: Click here.
Buy parts here.

Offline wmax351

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Re: I just bought a 2 valve K bike - what should I know?
« Reply #4 on: January 11, 2012, 12:44:38 AM »
bmp


For an update that I just added at the very top of this thread.


You forgot a "Fun Stops Here" mark for the rev limiter.
  • Albuquerque, NM
  • 91 BMW K75 Standard, 98 Moto Guzzi California EV
Bikes:
Current:1991 BMW K75 Standard, 1998 Moto Guzzi California EV11
Past: '83 BMW R65LS, '75 Honda CB550F, '69 Honda CB175, 1999 Royal Enfield Bullet 500, 1973 Triumph Tiger TR7V, 1971 BMW R75/5 in Toaster outfit, 1979 Harley Davidson XLS-1000 Sportster Roadster

Offline Honolulu

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If you do your own work make really really sure that you use the correct BMW fuel injection hose, 7x13 mm, and that you are really really really sure that the hose clamps are tight when you button it back up.  Otherwise a nasty fire can result.  DAMHIK IJK.

Offline Honolulu

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  • Posts: 9
Weak points of early K's include the ground wire from the trans case to the battery negative.  These can be clean and shiny, but fail because corrosion builds up inside the crimped ring terminal and prevents the juice from flowing.  Later Ks had a better ground line but you can also root up a proper braided connector just like real cars.

Another place to try if it doesn't want to start (because you can't hear the fuel pump running for two seconds each time you hit the starter button) is the connector at the low point of the tank on the left side.  Hans and Fritz played one of several of their little jokes on us there and installed a friction-fit connector in the vertical position, where its natural tendency is to fall out just enough not to make contact, resulting in no fuel pump and no workie.

Offline frankenduck

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Another place to try if it doesn't want to start (because you can't hear the fuel pump running for two seconds each time you hit the starter button) is the connector at the low point of the tank on the left side.  Hans and Fritz played one of several of their little jokes on us there and installed a friction-fit connector in the vertical position, where its natural tendency is to fall out just enough not to make contact, resulting in no fuel pump and no workie.

Only an issue on 85 and earlier bikes.
Once I had a Collie pup. Dug a hole and covered him up. Now I sit there by the hour. Waiting for a Collie-flower.
New to K bikes? Click here.
K Bike Maintenance & Mods: Click here.
Buy parts here.

Offline Masonjar

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Frankenduck, I recently became aware of this high altitude plug, and realized there has been one on my bike since I bought it! I live in Nashville, TN, and so did the previous owner, so it's a bit of a mystery to me. Anyway, I would like to remove the high altitude plug but I don't have the original plug and it doesn't seem to be a listed part on the fiches. What does the original plug do? Does it join the 2 wires or is it simply to keep dirt out?

If it is important, do you have any idea where I could get one? I'd hate to buy a whole used wiring harness off ebay....

I haven't done the simple test of pulling the plug out while it's running to see what happens, because I currently have the bike apart rebuilding the air intake and fuel injection system.

Thanks!

1985 K100RT.

Offline frankenduck

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All the altitude plug does is short two wires.  As they say in The Fatherland, it's a "contact ring."

The "original" plug is just a plastic cap.  It's really not necessary unless you plan on riding through water that's three feet deep.

(Only US models have the altitude plug.)
Once I had a Collie pup. Dug a hole and covered him up. Now I sit there by the hour. Waiting for a Collie-flower.
New to K bikes? Click here.
K Bike Maintenance & Mods: Click here.
Buy parts here.

Offline Masonjar

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That's exactly what I needed to know. Thank you!

Offline flutemanjohn

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I just read through the very helpful intro material. Thanks everyone, Flutemanjohn

Offline Sinky

  • The Laird of Fuengirola
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Great information. Thank you :)
  • Fuengirola,Malaga,Spain
  • 1987 BMW K100 LT
Run baby run....Please :)

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