Hey all, '85 K100 45k miles. 
I've searched a while with every key phrase I could think of (not to say I thought of them all) but I haven't found a thread talking about my exact concern. 

As the title states, I'm hearing a consistent rattling sound on acceleration, all throughout the rev range as far as I can tell until the engine drowns it out. 
At first, I was concerned about dry and worn splines, but it seems like that's more of an unloaded thing? 
Then I was thinking timing chain, but that also seems like it's not commonly heard during accel.
Then I was reading about the output drive rivets. I guess maybe? 
Everything I've read SO FAR doesn't quite align with what I'm experiencing, but maybe I've not read the right thread yet. It's definitely mechanical, and internal (ie not a loose clamp or something).

Anyway, otherwise the bike runs great. Idles smooth, pulls hard.. Though I have noticed sometimes the drivetrain feels a bit jerky.. Understanding how u-joints work (and having never ridden a shaft-drive before) I'm not sure if it's just k-territory, as it's not alarming. honestly most people probably wouldn't notice it, but I'm very detail-oriented, so... 

I really have no way of capturing video while riding, at least not safely.

Any expertise or suggestions on what to test is appreciated. I've not taken anything major apart yet, having only bought the bike this past winter (and no heated workspace or storage). 
*This is my first bike, but I've been reading all kinds of stuff on forums and facebook groups, and I've been working on cars and trucks for over 20 years, so feel free to get technical.

Edit: Wanted to mention that it has fresh fuel, engine oil, trans (I just got some additive I'll put in this week) and final drive gear oil, as well as new plugs. I haven't yet inspected the coolant or splines.

G

Guess you have the 6 rivet outputshaft, wich gonna tell you it's worn.
Time to change to the newer 12 rivet shaft.

Number 10 is your bugger;

https://www.realoem.com/bmw/en/showparts?id=0501-EUR-10-1983-K589-BMW-K_100_83_0501,0511_&diagId=11_4681

mmceorange wrote:I really have no way of capturing video while riding, at least not safely.

If the noise can be heard while wearing a helmet and riding, a recording device could be secured to the tank, handlebar or elsewhere on the moto. The sound file and random video, or a still photo, accompanying it can then be posted on YouTube and the link to it posted here. That's what many members have done.

Rattling on acceleration my thought is pinking.

Its consistent....I didn't think the output shaft bad rivets rattle like that on acceleration.

Another thought after someone pointed out the early Ks have a vacuum sensor that advances ignition timing by 12 degrees is that this is fitted to this K possibly causing pinking?

Incorrect ignition timing?

Bad petrol causing pinking? 

Bad alternator monkey nuts can be an issue but not consistent.

Bad injector can also cause knocking, suggest running the bike on 3 by disconnecting the plug on each one and running it so see the effect. The bad injector disconnected may show up.

Arlina wrote:Guess you have the 6 rivet outputshaft, wich gonna tell you it's worn.
Time to change to the newer 12 rivet shaft.

Number 10 is your bugger;

https://www.realoem.com/bmw/en/showparts?id=0501-EUR-10-1983-K589-BMW-K_100_83_0501,0511_&diagId=11_4681

Have I read correctly that this can be inspected by removing the crank case cover?

Laitch wrote:

mmceorange wrote:I really have no way of capturing video while riding, at least not safely.

If the noise can be heard while wearing a helmet and riding, a recording device could be secured to the tank, handlebar or elsewhere on the moto. The sound file and random video, or a still photo, accompanying it can then be posted on YouTube and the link to it posted here. That's what many members have done.

I only have my phone, but I'll see what I can do. I'm anticipating wind noise to overpower the rattle, though.
All this coming week looks to be fantastic weather, so I should be able to make some runs.

92KK 84WW Olaf wrote:Rattling on acceleration my thought is pinking.

Its consistent....I didn't think the output shaft bad rivets rattle like that on acceleration.

Another thought after someone pointed out the early Ks have a vacuum sensor that advances ignition timing by 12 degrees is that this is fitted to this K possibly causing pinking?

Incorrect ignition timing?

Bad petrol causing pinking? 

Bad alternator monkey nuts can be an issue but not consistent.

Bad injector can also cause knocking, suggest running the bike on 3 by disconnecting the plug on each one and running it so see the effect. The bad injector disconnected may show up.

Thank you for your suggestions. It does have fresh fuel, and I've run injector cleaner through the system. Like I said, it runs smooth and strong (though I have no other K experience to compare to), and the rattle, in my opinion, doesn't seem to be related to the combustion chambers or the like. However, I haven't read about ignition advance.. If you have the thread handy would you mind linking it? even if it turns out to not be the case, it would be good information.

I also forgot to mention that I've replaced all the oils in the bike (engine, trans, and final drive), but haven't yet dug into the coolant or splines.

Your easiest check is to see if you have a vacuum pipe coming from the front of the throttle bodies near no 1 cylinder, similar to the one off no 4 that goes to the fuel pressure regulator.

If you do have it, just as a rest disconnect it and get another vacuum cap and put it on instead and go for a ride to see if things change. Also try a plug chop, a fast run and kill the engine, pull the plugs and see the colour.

Your HES plate should probably be on the default setting.

If its pinking hard acceleration tends to increase the knocking and volume. Ks do not have anti knock sensors etc.

On the rivets, I also note that in the forum the knock they produce reduces/goes away after warming up.


Also, go under the engine and check your exhaust studs and nuts that none are loose.

Ah good info! I'll look into these things as soon as I can, thank you

In my (limited) experience, I got the impression that output shaft rivets rattled on idle ... almost as though, because there is no significant nor consistent pressure on the shaft and rivets, they are sorts of receiving an alternating (direction) pressure ... hence the rattle.

On acceleration, the gear is engage and the whole system is turning consistent in one direction and rattle disappears.

I removed my 6 rivet output shaft (1984 RT, 107K kms) and the movement was clearly identifiable. I then got a big punch and recompressed the rivets. The movement was eliminated. 

This is only offered as a temporary fix and is in no way a substitute for either replacement of shaft / rivets or a 12 rivet upgrade.

Long story short, +1 on the timing / pinking / pinging noise

Good luck with it

Given my recent experience I recommend checking the alternator bearings before engaging in any deeper engine related surgery.

geoff barnett wrote:Given my recent experience I recommend checking the alternator bearings before engaging in any deeper engine related surgery.

Also a good one
Also check the monkeynuts and the find in the alternator clutch housing.

Arlina wrote:

geoff barnett wrote:Given my recent experience I recommend checking the alternator bearings before engaging in any deeper engine related surgery.

Also a good one
Also check the monkeynuts and the find in the alternator clutch housing.

Agree on that but the rattle ended up being a loose exhaust flange.....stud and nut gone, other nut loose and flange rattling.

Olaf,was spot on then,and we all know loose NUTS can be a real headache in more ways than one

Ducktape. No worries

Well folks, I think I've found the source of the rattle... A DAMN NUT ON THE MUFFLER.
I noticed it sounded like it was more on the left side, so when I parked it idling, I searched around and noticed this




Weather is going to be pretty wet the next few days, but when I get a chance I'll take it out to confirm that's all it was.

Thank you for all the suggestions though, I'm pretty new to these bikes so all information is welcome and useful.

Though in listening more closely, I think I'm also hearing some rattle on deceleration up front of the engine. Also, It smoked a lot after sitting on center stand for several days.. I may be doing a rebuild this winter for peace of mind. Are there any full rebuild kits out there?

Easy Tiger,at 45000k the engine is not RUN IN yet,an over active imagination and very good hearing can be a pain.Firstly, Full Compression test,check vale clearances
Now you have a starting point.Ks smoke for fun,if it clears all is well.Running engine when on centre stand WILL produce many strange noises (REVERBERATION) 
Take it for a good run and let it rev,when you get back Kill the engine don't let it idle
plugs out and inspect them.With a bit of Lady Luck things will be ok 

Yes I do all those things (well I haven't done compression and leakdown yet), except not letting it idle after a ride.. Why is that?
Sounds I'm reporting are while riding, not just revving on the center stand. I know they smoke on first start, but this time it was much more than usual. But yeah, it eventually went away after a few minutes and didn't smoke again the rest of the day or day after. I simply don't know the condition of the engine or how well it was taken care of. The bike will be down for major modifications this winter anyway, along with painting. So it would be a good time to refresh/replace gaskets, seals, and bearings, do some upgrades (like the output shaft) and whatever else.


By the way, a couple weeks ago I also picked this up

With plans to keep it pretty much stock because it is SO DAMN COMFORTABLE lol

The bike in picture looks very good nice find.PLUGS this is the best way to find if engine/fuel mix is good,stopping and letting engine idle can show sooty plugs.
Best of luck with your plans for the bike

Ahh ok. Thanks.

Yeah the 1100 is my favorite color combination I've seen (factory, at least) so I had to jump on it. I think that bike looks off without the panniers. Unfortunately, one is cracked, but still functional. Both side panels' clips are broken, so they don't stay on very well. Body parts have dings, scratches, and sand blasting, and missing random fasteners and clips, but nothing serious.
Many people suggest swapping the K100's center stand to one from an 1100, but I find the K1100 to be far more difficult to get up onto the stand.. Maybe it's just heavier, but I'm now leaning towards keeping with the K100 stand on the K100.

Me too the k100 stand with curved legs is much easier than the k1100 straight leg
type.Sounds like a girl i once knew 

How long was it sitting before you got it? Bricks don't like sitting around, and can suffer from sticky rings which can lead to smoking. Often with more miles the smoking will reduce or go away. There are also various additives that others have used to fix sticky rings, Seafoam, MMO or running a high detergent diesel oil for a short period. Early K100's apparently didn't have pinned rings which can also contribute to smoking.
Regards Martin.

I don't know how long it sat before I bought it, but that was back in December. I've been riding it a couple months now. Before this smoking incident, it had been sitting only a week on the center stand.

I'd either give it more time or try one of the methods for unsticking rings.  Due to the fact that the rings aren't pinned and if the rings are sticky, it's possible that some of the rings gaps have aligned leading to more oil use and smoking. We don't have Seafoam or MMO in OZ but someone in the US will chip in which is the best way to go. A mates Brick was a prodigious smoker and it took well over six months for it to reduce. A couple of months is not enough time to have much effect, distance and speed travelled will have more impact than time. 
Regards Martin.

mmceorange wrote:Well folks, I think I've found the source of the rattle... A DAMN NUT ON THE MUFFLER.

You won't be the first one to be caught out by that little bastard!

Glad you found it.

Wellllll I'm not sure of that yet lol, I haven't been able to get a ride in since discovery to confirm. Part of me hopes that's all it was, but another part of me hopes that's not all it was

mmceorange Perhaps you have solved your problem, but here's a way to check the output shaft rivets without too much effort .... actually little effort; it's like a couple of hours if that. Got to the top of the following thread and read all the posts. 

https://www.k100-forum.com/t13961-output-shaft-rivets-anti-backlash-mechanism-again#164666

My opinion your problem isn't  output shaft ... pinking or monkey nuts 

Good luck

Thanks for the link, that's helpful. I will likely upgrade it anyway this winter when the whole bike is apart, just for one less thing to think about later.

Hi, I am in Mass and have a 12 rivet output shaft with I believe the correct bearing that I would sell if you need it.

So anyway, it seems to have been that pesky little nut. I feel so dumb.. but it happens!

I've since tried out an aftermarket collector and slip-on muffler. The engine definitely doesn't prefer this setup, and I suspect I may have developed a vac leak somewhere as its performance has been slowly degrading, and starting is becoming more difficult. So I have to figure that out now. But that's not related to this thread...

yankeeone wrote:Hi, I am in Mass and have a 12 rivet output shaft with I believe the correct bearing that I would sell if you need it.

I am going to PM you about this, but my plans for this bike might require me to upgrade to a 16v trans (for paralever), and I want to make sure the output shaft doesn't need to be specific