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Motorcycle Woes

Discussion in 'The Lounge' started by Bipolar, Sep 18, 2020.

  1. Bipolar

    Bipolar Well-Known Member

    I fired up my 35 year old BMW K100RT today and took it to the shop to change the oil
    before the riding season is over here in the north. I never store an engine with dirty oil
    in it. I parked it outside and went in and opened the door. When I went to fire the engine
    up the starter would spin but would not crank the engine. I changed the oil and had the
    guys give me a push start to get it going. I got home and parked it in the man cave.

    Searching the internet it looks like a common problem with the K bikes. The starter
    sprag clutch has gummed up over time. The bike has 57,000 kilometres on it
    and has been babied and over serviced. The clutch spline and the drive shaft splines
    are past due for being lubed as well. Looks like I have another winter project.

  2. Footloose

    Footloose Well-Known Member

    If the starter dies or other electical parts, try a Bosch distributor with the items component no. It will probably be quite a lot cheaper!
  3. PeteRob

    PeteRob Well-Known Member

    I don’t know anything at all about bikes but the fault reminds me of my first car which needed a length of wood and a club hammer to encourage the starter solenoid switch to engage.
  4. dream_police

    dream_police Well-Known Member

    I remember that on my Escort. Am I right in remembering putting the car in gear and rocking it to and fro was also for the same reason?
  5. PeteRob

    PeteRob Well-Known Member

    Might be the opposite problem. Starter solenoid switch engages the starter motor with the flywheel. If it sticks without engaging then the starter motor just goes around by itself. If it doesn't disengage (sticks the other way) so the starter motor is permanently coupled to the flywheel then maybe you could release it as described but I'd expect the starter motor to break quite quickly. It isn't going to stall the engine once the fly-wheel is going round. Rocking the car with the car in gear could also be a way to release seized drum brake shoes. If I remember correctly the hand-brake operated on the rear brake shoes. If the car was parked with hot brakes in wet weather the shoes could stick. It had hydrolastic suspension. In reverse, with the rear brakes locked on, the whole back of the car would rise dramatically before the brakes released with an almighty bang.
  6. John King

    John King Well-Known Member

    I have two of these K bikes, both are K75 3 cylinder versions. Not the same as the OP, but basically the engines are the same, just one cylinder less!.
    One and possibly the main reason the sprag clutch 'jams up' is due to lack of use. For non bike readers a sprag clutch is used by this starter motor. How this clutch works is by centrifugal force causing teeth to move out from the centre and engage with the flywheel. Normal starter motors have a solenoid or Bendix drive to engage the starter with the flywheel. A sprag clutch is not part of the starter motor per se.
    They are most definitely NOT the same design or operation as a car starter motor and will not work if it is clouted with a piece of wood.
    Bosch parts are used and whilst some BMW car/bike parts are interchangeable, (Fuel pumps come to mind,) a Bosch dealer will almost certainly refer you back to BMW.

    Anyway back to the reason.

    If a bike is not used regularly and when it is, does not get hot and I mean really HOT! A short trip to the shops or commute to work is not a way to ensure the bike get really hot! The oil will start to gum up and cause the clutch to fail. This is irrespective of old or new oil! The brand of oil and the grade may also have an effect. BMW State that the recommended oil should be simple mineral 20/50 or 15/40. Use of the current synthetic oils will only result in costing you more.

    Both of my bikes have been used more extensively than yours, one has covered 62500 miles and the other 60000 miles (not kilometres). I bought both of mine in 2012, each with less than 20,000 miles. The oil has to get hot to boil off any condensation or it will sludge up. These are big, bulky, mildly tuned, liquid cooled engines on a bike and take quite a long time to get really hot.

    You say that your bike is 35 years old which makes it 1 year older than my two. This to me is a clue that the bike has been mollycoddled through its life, 57000kms in 35 years means it has on average only covered on average 1250 miles a year in all that time. Or about 6 full tanks of fuel. Both of mine cover at least 4 times that distance per year. BMW 'K' series bike engines are generally bullet proof, and possibly one of the best designs they have ever made. Many will cover well over 150,000 miles and will still be running well. I know of one K1100 LT which has a slightly bigger engine capacity than yours which has covered a quarter of a million miles and this with only regular servicing. (The K Series engine was derived from a Peugeot car engine!)

    The sprag clutch is a tiny problem and although known, certainly is not 'common'. Unfortunately to rectify this, it means the gearbox has to come off to get to it and that will be expensive on it's own.
    Last edited: Sep 19, 2020
  7. dream_police

    dream_police Well-Known Member

    It certainly wasn’t a brake problem. It was to do with a starting issue.

    I have just googled it. Rocking a car in gear was for a starter motor issue.
  8. John King

    John King Well-Known Member

    This will NOT WORK with a motorcycle with a sprag clutch which was the original question.
  9. dream_police

    dream_police Well-Known Member

    The conversation had moved on. The OP wasn't a question. He was just telling us about the bike and the problem.
  10. PeteRob

    PeteRob Well-Known Member

    Could be worn flywheel or missing tooth needing to advance it. Just a guess.
  11. John King

    John King Well-Known Member

    It is not a flywheel or missing tooth problem either, believe me I know K series bikes very well. I have been working on them since my first one in 1985/6
  12. PeteRob

    PeteRob Well-Known Member

    We are off at a tangent talking about cars we once owned. Nothing to do with bikes.
    dream_police likes this.
  13. neilt3

    neilt3 Well-Known Member

    So what else is new ? :p
  14. Bipolar

    Bipolar Well-Known Member

    The bike certainly has been coddled over the past few years. I seldom ride it. I try to ride it
    enough over the summer that the gas tank is empty so I can store it for the winter with fresh fuel in it.
  15. Learning

    Learning Ethelred the Ill-Named

    I suspect that this bike problem is not a woe. It is an excuse for a winter project in a heated garage sized man-cave. You might even need some new engineering toys to complete the job.
  16. Bipolar

    Bipolar Well-Known Member

    I should have all the engineering toys I need after a 46 year career as a mechanic.
    One of the things that pleases me is that BMW still supplies parts for 35 year old motorcycles.
    Learning and John Farrell like this.
  17. John King

    John King Well-Known Member

    So long as you have deep pockets. A new combined water/oil pump is eye wateringly expensive - around $650 us Dollars. An electronic trigger for the K series ignition is about $400 US dollars.
  18. GeoffR

    GeoffR Well-Known Member

    Sprag clutches are by no means confined to motorcycles. For the benefit of those not familiar with them it is probably sufficient to say that their operation has little in common with the engagement of a car engine starter. There are some videos on YouTube that explain their workings and why belting it with a club hammer and a lump of wood will do little more than provide a workout for your arm.

    Rocking a car in gear is a method of disengaging the bendix gear on a car starter motor, wacking the starter motor with a mallet sometimes worked too. More recent cars have a different system, the solenoid engages the pinion with the flywheel and then connects the motor to the battery. The difference between the systems is that the later starter motor is a permanent magnet device and can turn the engine without a run up. Older types can’t, hence the bendix gear that doesn’t engage until the motor is turning at a sufficient speed.
  19. SqueamishOssifrage

    SqueamishOssifrage Well-Known Member

  20. John King

    John King Well-Known Member

    Any motorcycle, or for that matter any internal combustion engined vehicle that has not turned a wheel in anger since it was made 43 years previously, could be a recipe for never ending woes. Over that time span, oil seals, fuel pipes, certainly tyres and possibly certain internal mechanicals will have deteriorated to the point of being unserviceable. Internal corrosion is also a possibility. Oils will have semi solidified, grease points likewise, so it would need a complete strip down to make it fit for use. Even the unique Norton Commando engine mounting to the frame, the so called called 'Isolastic' mounts where engine vibration was damped out, would almost certainly no longer work as intended

    I certainly would not buy one like that even if I had the money. But there again I am not a collector with funds to waste on an otherwise museum piece.
    Last edited: Sep 20, 2020

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