K100 noise/ power loss

[Oehmig]

Hey guys. I good friend of mine has been riding a 92' k100 for the past few years. He recently called to tell me that the engine was making noise (not knock or tick butunusually loud clatter. He road it a few miles this morning (bad idea, i agree) and said that suddenly the engine lost all power and he had to park it. No smoke apparently, no pop. Just sudden power loss. I'm trying to help him diagnose the issue and get it resolved. Any ideas what these symptoms might suggest? Thanks.

[Martin]

Possible alternator monkey nuts failure , hence the clatter. Power loss due to battery going flat because alternator has no drive.
Regards Martin.

[Laitch]

Do a compression test right now. Update with results.

[Oehmig]

Thanks. Doing compression test this afternoon and will report back. If its alternator nuts, will it be obviously loose against the engine? Before the engine stopped he said he mistook the sound for an exhaust leak. As if the header were cracked and it sounded exhaust related.

[Martin]

Just remove the alternator, it's probably a good idea to check them any way. Also check all the fluid levels. You might be able to hear and trace the noise when doing the compression test. Do the compression test at full throttle.
Regards Martin.

[Martin]

I forgot to add if you were loosing power due to the battery going flat, you will now be unable to crank it over. Without a fully charged battery you are at risk of welding the starter relay points closed. Check the condition of your battery.
Regards Martin.

[Oehmig]

So heres the update. I removed the battery and gave it an afternoon on the tender. Got her up to 13.4v and reinstalled it on the bike. Tried to start it, but it didnt turn the starter or even try to crank but all the lights and gauges were on. Then a little whiteish smoke started down by the exhaust/coil/starter area. Immediately disconnected the battery. Was hoping that testing on a fully charged battery would reveal bad alternator/monkey nuts as the issue. Still waiting to test compression but I'm at a loss with these symptoms... any ideas?
 

[Laitch]

Trace the negative battery cable from the battery terminal to its point of ground attachment to be sure that it is tight and clean. Disconnect it at that point then reconnect it. Trace the ground wire from the master cylinder to its point of attachment to check its integrity. Measure your battery output and if it is sufficient, try again.

Has this engine been out of the frame since you've owned it?

[Oehmig]

Thanks guys. Yes visual inspection did reveal melted insultion of the red wires feeding to the positive terminal but it appeared that it was from a previous incident. No exposed wire there currently. I checked the ground connection before disconnecting but will do a thorough clean before my next attempt. Did that occur from a bad ground? What was smoking exactly? I made no changes other than charging the battery...

[Laitch]

I checked the ground connection before disconnecting but will do a thorough clean before my next attempt. Did that occur from a bad ground? What was smoking exactly?

Light her up again and post a video of the smoke. There's been nothing exciting coming here from Netflix lately.

[rbm]

It's been known to happen that the binding post on the starter can short inside the starter itself.  Do one of two tests.  Either disassemble the starter (if you haven't already done so) to inspect the electrical connection to the brush.  The short happens in the insulation of the binding post so look at it carefully.  Alternatively, electrically check for a short to the case at the binding post after removing the bike's wiring.

[Oehmig]

Lol. Well laitch, i agree that would be quality, albeit heartbreaking, entertainment, but if theres anything about the K bikes on netflix, i'd be all over it... youtube maybe ;) until then, peaky blinders is pretty damn good.

Thanks rbm. I've read several threads about the starters posts welding and this same bike had that issue a few months ago. A few whacks and back to tentative normalcy. The owner didnt mention that the starter was continually spinning when this began but obviously with the poor battery issue, symtoms of alternator failure and no effect from the starter, i will focus my efforts there. Thanks for your help and humor guys. Will update my findings and compression results tomorrow

[Vespa no more]

Starter can be reluctant to come out

Make up something like in pic. Rod no thicker than 5 mm and lever it out with screwdriver. There are some posts on dismantling starter motor and alternator.

Keeping alternator rubbers in place for reinstalation can be problematic. Small amount of RTV silicone will hold them in place and space them apart as per 2nd pic if needed. Mark the gap in the rubbers on the outside of the cup to align with (hopefully not damaged) drive vane.

Everything's so logical with hindsight

Guy

[Oehmig]

Well i opened the starter and the inside reeked of electrical burn. The wire connection running into has fried and melted. Bearings were bad etc... put another starter that i had on, still didnt turn the engine. Pulled the alternator and it seemed fine. Except that when mounted in the engine, it wouldnt spin. We tried turning the shaft/cup that seats the alyernator, no spin. Took of the right side engine cover to inspect the gear and this is what we found. Aside from deposits of metal, stuck gear, and locked up cylinder, one of the rods was cooked to the point of dryness. Oil of all the others, none on the one. Thanks for all your help guys.

[Laitch]

Oil of all the others, none on the one.

Oil starvation. Tough break. Thanks for the update, Oehmig.