Hi guys,

I'm new here and I'm glad to be a part of the forum 
I never had the need to be on here since my knowledge isn't that great to resolve your problems, and I never had any problems of my own... 'till now unfortunately.

I did great research before deciding what my next motorcycle would be, after an unfortunate crash on the Isle of Man and wrecking my previous Honda. 
I chose for the almighty Brick, almost bulletproof, and great for touring.
Bought my K100LT (January 1989) from the first owner, she looked great and had the original cases.
First things I did was changing all the fluids, filters, battery and the notorious spline lube.

Now she makes an awful knocking sound on cold start, it goes away on higher RPM's as you see/hear in the video (the frequency of the knock increases also if I increase engine speed a little until it fades away). 
Once the engine is warm, it's gone. 
Power delivery is fine, no other complaints.
I removed the heat-shield, because it rattles a little bit.
The knock is really audible near the alternator, and also on the other side (the left side of the engine).

Had a BMW-guy look at the video and he thinks it turns on 3 cylinders in the beginning (he couldn't hear it in real because my engine was warm once I got to him). 
I think it sounds different than that. 
What could be the problem? Perhaps something like a valve or such (but hey, I'm no expert)?
I'm not certain and I plan on checking my valve clearance, synchronizing the throttle bodies very soon.

I had to post it here because my sleep is suffering from this 

I started filming right after I started her.
https://www.youtube.com/watch?v=3rfcGdKrvVE

Hi mate
that sounds exactly like mine did. Most of these bikes have a bit of a rattle that goes away after they get warm and running at a few revs.
I replaced the rubber "Monkey Nuts" or cush drives, which are just inside the engine end of the alternator. Sounds like a hard job, but if you take the battery and it's cradle out you can get at all the 3 bolts.
Mine is a lot better after doing that, but I still have a small rattle. Suggestions are that my drive shaft rivets could be wearing. (Search that on the forum), a not uncommon thing to happen.

The other solution is to not start the bike until you are ready to go, then just jump on and take off, no warm up means less rider stress.

Alternator cush drive!

Thanks Olaf and RT!
I will try that as soon as possible and keep this TS-topic updated

RT wrote:The other solution is to not start the bike until you are ready to go, then just jump on and take off, no warm up means less rider stress.

Haha indeed.

There doesn't even have to be anything wrong with my car or bike, but just thinking about it already makes me crazy  
But hey, I suspect I'm not alone here in that aspect

Part #17 is a spring that is part of an anti-rattle mechanism on the output shaft.  When they get weak, the gear #18 that is supposed to take up the slack in the gear mesh starts to move around making a knocking/clanking sound.  I have the problem on my K75.  Supposedly, it's not uncommon and doesn't hurt anything.  Hasn't caused any problems on my bike.  Mine occurs between about 1200 and 1900rpm and doesn't go away when the engine warms up.  Next winter I plan on dropping the engine and taking care of it.

I agree with Point-Seven-Five. I have exactly the same noise and exactly the same symptoms and I just ignore it. Last time I rang Motorworks I mentioned this and the advice from them was also not to worry about it. Search for 'diesel knock' on the forum and you'll find quite a few posts about it.

If it was broken or misaligned monkey nuts (alternator cush drive) you'd really know about it. That sounds like the mechanical end of the world on the top right of the engine. Been there... It's really easy to get the alignment wrong when pushing the alternator back in if you don't keep an eye on the marks.

Sounds like the idle is way too slow, this would make it sound worse. Have you balanced the throttle bodies?

Mike

mike d wrote:Sounds like the idle is way too slow, this would make it sound worse. Have you balanced the throttle bodies?

Mike

Do you remember how terrible the early Honda 4s sounded when the carbs were out of balance and the tickover a shade too low?

Us old gits will remember for sure. Can't remember what I did this morning though.


Mike

I installed new cush rubbers and a 12 rivet output shaft with new rubbers in it too. 

I have a slight knock like that under the same conditions. maybe not so loud, but very much like that from the alternator area.

The alternator bearing in the bell housing is one of the only bearings I didnt replace. I often wonder if its got anything to do with that, but prob not.

Im not worried about my knock and sounds like the consensus is your's is within spec for these old girls too

Hi guys! 
Had some time today, I took out the alternator and let it run with only the battery...the knocking sound is still there.
I also checked valve clearance, and they were all within margin.
Only thing remaining on my to-do-list is syncing the throttle bodies (after I get the cover and those 2 irritating gaskets on  )

Point-Seven-five wrote:Part #17 is a spring that is part of an anti-rattle mechanism on the output shaft.  When they get weak, the gear #18 that is supposed to take up the slack in the gear mesh starts to move around making a knocking/clanking sound.  I have the problem on my K75.  Supposedly, it's not uncommon and doesn't hurt anything.  Hasn't caused any problems on my bike.  Mine occurs between about 1200 and 1900rpm and doesn't go away when the engine warms up.  Next winter I plan on dropping the engine and taking care of it.

I second this, from experience. If/when you replace the spring that supposed to keep the two gears meshing (quietly) check if you have the output shaft assembly that was an upgrade. If not, you can convert it to the upgraded version. 

Getting the cursed output shaft out is the worst part of this procedure. Otherwise, it's easy and you can kiss that clatter goodbye which is damned near priceless.

Since it's quite a job I will leave it 'till my next spline lube.
Should the 12rivet-output shaft be bought new or secondhand?
I suppose it's a hefty price if new... but on the other hand when you buy a used one, isn't the risk of a lot of (invisible) wear too big?

Thanks a lot guys!

mike d wrote:Us old gits will remember for sure. Can't remember what I did this morning though.


Mike

This is an early sign of oldtimer disease.