Last October I took my K100RT to the shop where I work to change the engine oil before parking the bike for the winter.
I shut it off outside the shop and went in and opened the door. When I went to start it to drive it in side it would not crank
over but I could hear the starter spin but not engage.
 I changed the oil and got a push to get it started and drove the bike home and parked it in the man-cave for the winter.
 Last week the new sprag showed up so I stripped the bike down and replaced the sprag. From start to finish it took 
about 14 hours. I can't believe how many parts had to come off. Its back up and running again.

I should have ordered a new set of the six bolts that hold the clutch together. They are 7mm fine thread metric bolts.
an odd size that none of the local industrial stores could even get. The allen hex distorted removing them, I ended 
cutting slots in the heads with the milling machine and was able to torque that way.

Another month and the snow will be gone and the K bike is back on the road.

Bipolar

You reused the clutch bolts and cut slots in them?

Did you replace the rear main crankshaft seal when you were in there?

Yes I replaced the rear seal with the updated seal.

Bipolar wrote:Last October I took my K100RT to the shop where I work to change the engine oil before parking the bike for the winter.
I shut it off outside the shop and went in and opened the door. When I went to start it to drive it in side it would not crank
over but I could hear the starter spin but not engage.
 I changed the oil and got a push to get it started and drove the bike home and parked it in the man-cave for the winter.
 Last week the new sprag showed up so I stripped the bike down and replaced the sprag. From start to finish it took 
about 14 hours. I can't believe how many parts had to come off. Its back up and running again.

I should have ordered a new set of the six bolts that hold the clutch together. They are 7mm fine thread metric bolts.
an odd size that none of the local industrial stores could even get. The allen hex distorted removing them, I ended 
cutting slots in the heads with the milling machine and was able to torque that way.

Another month and the snow will be gone and the K bike is back on the road.

Bipolar

14 hrs only...my compliments! Did you reused clutch nut and all other components? Do you have the BMW special clutch plate centering tool?         I have some different issue, because sprag cluth seems to work but starter motor can not turn engine ONLY when spark plugs are out and engine is in a certain position. Seems like engine has some additional drag somewhere because strarter, cables and battery are checked :-(    Thank you if you have any idea. Greg

Can you monitor the battery voltage with a voltmeter while cranking the engine.
You could have a weak battery or a bad connection somewhere.

Bipolar wrote:Can you monitor the battery voltage with a voltmeter while cranking the engine.
You could have a weak battery or a bad connection somewhere.

I used my van's battery with the van engine in operation. So 80Ah battery in charge -> aprx. 14 Volts.   Direct connection to exclude any bike electric issue.    3 out of 3 starter motor behave in the same way. Not turning or only in some cases (no sparks etc) when mounted in place.                     If I pull out starter motor, during cranking (only starter motor, no fuel pump etc connected) amperage goes up to 180 at start (Amp meter range is on 200m) and stays around 110 when starter spins well. Connecting bike to the battery, Voltage drops from 14 even to 6 at starting and then back over 11 V when starter is spinning. Always with starter out of place=with no load.

I can't see three bad starters. You are cranking it with the clutch released in case the drag is from the transmission. 
The alternator could be the problem a bearing failed or rust inside the alternator making it drag.
Do you know the bikes history?

Terry

Bipolar wrote:I can't see three bad starters. You are cranking it with the clutch released in case the drag is from the transmission. 
The alternator could be the problem a bearing failed or rust inside the alternator making it drag.
Do you know the bikes history?

Terry

gearbox, half of the clutch, alternator and water\oil pumps are removed.         Bike is\was OK, I owe it for 15 years. Only minor services and routine as previewed till now.

You should be able to rotate the engine by hand from the clutch end.
Was is stored for a while? Did this problem just occur?

Bipolar wrote:You should be able to rotate the engine by hand from the clutch end.
Was is stored for a while? Did this problem just occur?

Bike was stopped for 2 weeks. Worked perfect till the last ride, never had this issue before.   Engine can be rotated from the clutch end, even by one hand, if I put my near to max.  force.    (and sprag clutch looks ok: free on left \ engages on right turn)

I have no idea what else it could be.
Hopefully someone else here can help.
Terry

Did you open the gear box at all?

Could it be the output shaft rivets? Isn't this an early model 100 with the 6 rivet output shaft?

92KK 84WW Olaf wrote:Did you open the gear box at all?

Not opened, only detached/dismounted.  But it works perfectly and has no influence on cranking the engine in neutral. (now in gearbox connector wires are bypassed, simulating neutral gear for the ignition system, but has also no influence when using direct connection to starter motor)

Point-Seven-five wrote:Could it be the output shaft rivets?  Isn't this an early model 100 with the 6 rivet output shaft?

It is a K75 from 1991. What is the issue exactly about the rivets? Engine can be turned by hand from clutch end and no strange noises heard.

Don't pay any attention to my output shaft post.  I was reading the title of the thread where it referred to a 1985 K100.

You should put the model and year of your bike in the signature line in your profile. That way people like me will know what we're commenting on.