New to me K100 knocking

[Crow]

Hi everyone I have read a few posts on the alternator and 6 rivet issue etc but would like your opinion on what in going to explain .. I've just yesterday picked up a 1988 k100lt . Been off the road a while (20 years ) the guy I got it off put new injectors . Fuel pump on her to get her running . She starts first push of the button and idles OK but think she needs a bit of fine tuning and full service etc .. my question is or advice I'm looking for from more experienced guys is on a cold start she starts great and engine is quiet for about 30 seconds to a minute then a knocking rumble starts at around the alternator area on right hand side which quietens down a bit after I rev her to about 2000rpm ish . The oil is black and she been off the road a good few years . I don't know any history so I'm just doing things as I go . Full service kit is on its way but the knocking is concerning me a little . 85000 miles . Starts on the button ... thanks .

[Laitch]

. . . a knocking rumble starts at around the alternator area on right hand side which quietens down a bit after I rev her to about 2000rpm ish.

Diagnosing the source of a problem by the sounds it seems to make is difficult when the sounds can't be heard.  One person's rumble can be another person's clack. Making a video that includes the sound, posting it as public video on YouTube, and providing the link here can sometimes be helpful.

If the knocking stops or diminishes when the clutch hand lever is pulled while the engine is idling, the sound could possibly be made by worn alternator drive cushions allowing the alternator cup blades to knock together with the alternator drive blades. The cushions are known by many around here as monkey nutz. Below is an extreme example of the result of procrastination in resolving that particular issue.

No noise from these.


Lots of noise from these—a combination of sounds like dice rattling in a cup, a baritone singer gargling with marbles, and a Riverdance session at the retirement home. Not a difficult job to remedy though.

[frankenduck]

You obviously want to change the oil on a bike that has been sitting that long if you haven't already.

Even with new oil it will go dark very quickly on a K bike so do not let that concern you.

[daveson]

No knocking, then knocking after about one minute. One of the possibilities of this symptom is a k100 running on three cylinders, of course the power would be down in this situation. Maybe lacking spark or fuel, maybe check fuel first since that was tinkered with previously. Using a screwdriver as a stethoscope, you should be able to hear all four injectors ticking.

[Crow]

Appreciate the replies . I'll be at it tomorrow and thursdy to strip it of the tupperwear and change out the oil and filter then check injectors ,and set the mixture screws etc . I'll take a video of the cold start and post it on here to hopefully let you hear the issue I'm talking about and hope it's the alternator . Curious if I remove the alternator anyway can I still fire the bike up to eliminate the alternator ?

[daveson]

Yep.