disturbing k100 engine rattle

[bmwrider75]

Hey all;

Just bought my first K100 (a 1985 K100RS with a sidecar), and it makes a horrendous clattering rattle at idle, seriously like someone has neglected to attach one of the connecting rods or something. It thunks, whacks, clatters, and sounds so awful that it's embarrasing to ride it through town.

Out on the road once it's revved up over 2k, it seems to be smooth (ish) and very powerful. I've ridden it about two thousand miles so far and the rattle hasn't changed, but it sounds like the gates of Hades.

I know airheads pretty well but next to nothing about K's...anyone that has an idea about how to fix this noise, I sure would appreciate it...

It's a 1985 K100RS, with 85k miles. It's been well looked after with full documentation and dealer-servicing (though I can't hardly believe the PO tolerated this sound!)

thanks,

[35634]

sounds like the altermator dampers-#8 in the illustration. Little rubber pillows in
the coupling that disintegrate and let the drive rattle around

[Gilly]

Ummm, there's another name for those you know.
My thought was the tensioner for the timing chain. Can you try to tell if it's coming from the front or rear of the engine.
Gilly

[Gilly]

Oh, and it's only "smooth-ish" because it's a K100. If it was a K75, it would be smooth.

Gilly

[deilenberger]

The other possibility - especially since it's a '85 - the anti-rattle gear on the output shaft is rattling (this is a rather long story of failed engineering where BMW went through 3 designs of a gear assembly that's supposed to stop rattling noises between two gears - and did just the opposite.) I believe the '85's still had the earliest of the failed designs.

If so - nothing to be done about it except keep RPMs above 2k. There is also the possibility the output shaft coupler gear - which is riveted on the drum the cush-drive lives in is coming loose. There was a chap here a month or two ago who had his fail completely which results in no output from the engine, even though it's happily running. He's replacing the engine, easier/cheaper than fixing it. Clue for that is rivet heads in the oil.

[bmwrider75]

I was reading about the anti-rattle gear/output shaft - most of those posts seem to indicate that that noise will settle down when the engine warms up, and it's described more like a gear rattle. This is clearly a mechanical thunking - really a terrible sound - and it doesn't change with the clutch pulled in and it doesn't change when the engine is warmed up.

I don't mind a noisy bike - after all I've ridden airheads for years - but clearly something is wrong. I hope it's the alternator bushings. Hard to tell where the sound is coming from - I would guess more "rear" of the engine but it sounds like it's coming from everywhere. It clunks hard enough sometimes to feel it through the handlebars!!

Are those alternator bushings hard to get at to replace?

(and yeah - I rented a K75 once - still miss how smooth that motor is! Smoothest ride I've ever had. I think this K100 can be smoother though - needs a tuneup and throttle body sync, etc.).

dc

[cayuse60]

.....Are those alternator bushings hard to get at to replace?

(and yeah - I rented a K75 once - still miss how smooth that motor is! Smoothest ride I've ever had. I think this K100 can be smoother though - needs a tuneup and throttle body sync, etc.).

dc

No... remove alternator.

[mrich12000]

It's old. and the ruber dampeners are worn out, ez fix...:thumb

[PGlaves]

It's old. and the ruber dampeners are worn out, ez fix...:thumb

Here is what old ones look like.

Find the April, 2008 issue of the ON and look at my Benchwrenching Column regarding Monkey Nutz.

[PGlaves]

Here is what new ones look like.

[PGlaves]

Here is where they go!!

[godzilla]

My '85 K100 has been doing this since I bought her with 69K. She now has well over 140K and she still does it, only when cold at a low idle. I turned up the idle screw a little to bring up a few notches and she sounds much better.

[bmwrider75]

thanks all for your helpful suggestions.

Paul, thanks very much - I looked up the April 08 article and will try and remove the alternator tomorrow, now that I'm home from the road.

Will report back with findings!

dc

[bmwrider75]

thanks all for your helpful suggestions.

Paul, thanks very much - I looked up the April 08 article and will try and remove the alternator tomorrow, now that I'm home from the road.

Will report back with findings!

dc

Ok, just finished removing the alternator (though I couldn't figure out how to disconnect the big black plug for the (EFI??) that sits below the toolbox. I really need to get a service manual for K bikes!!).

To my great disappointment, the monkey nuts were in excellent shape and there was no damage to either the alternator clutch housing or the driving dog on the engine.

I hooked up the battery and started the engine again, running it without the alternator, and the death rattle persisted. It sounds as if the crankshaft is slapping back and forth inside the bottom end, I can't really describe it, but it's more than just a rattle - it's a loud, heavy clunking and crashing about. Now I've never heard any other K100's, but I find it hard to believe that this is a "normal" noise.

I drained the engine and gearbox oil and did not see any dramatic evidence of metal - certainly none in the engine - the normal amount of clustered fine fuzz on the gearbox drainplug with nothing really coarse or granular.

Amazingly the bike completed a 2500 mile journey with a fully loaded sidecar with no major problems.

Where should I look from here?

Many thanks,
dc

[35634]

Wow. Something major like bearings it seems the engine would of self-destructed
by now. Not too hard to pull off the crank cover and have a look see. Or still could
be timing chain. Got good oil pressure?

[deilenberger]

Where should I look from here?

Many thanks,
dcI believe I gave you the other more likely possibilities in a posting above.

[bmwrider75]

I believe I gave you the other more likely possibilities in a posting above.

Thanks - I did see that - I was asking more if I could confirm either possibility without simply swapping out the engine (i.e. short of seeing rivets in the oil, is there a way to tell whether the output shaft gear is failing?).

Dan

[deilenberger]

Dan,

It's been claimed - and I haven't done this so it's strictly second-hand info - that you can see the rivets, barely, if you remove the crankshaft cover. No knowledge beyond what I heard, never BTDT.

If it is the rivets going bad - probably less expensive to find a good used engine and throw it in. $300-400 should get you an engine in good condition.

[RICHO2006]

I need to check if the rivets on the output shaft are still okay. In the post above Don indicated

"It's been claimed - and I haven't done this so it's strictly second-hand info - that you can see the rivets, barely, if you remove the crankshaft cover. No knowledge beyond what I heard, never BTDT."

Does anyone know for sure if you can see the rivets when the crank case cover is removed?


Thanks

Richard Flood

[Dennie]

I'm going out of town this weekend, but if you're in no hurry, I'll look at my k100 (85) and see if you can, if so I will take some picks for you. it will probably be wednesday though.

[RICHO2006]

I'm in no hurry. When ever you get around to looking will be fine.


Thanks


Richard

[VanFrederick]

Maybe this is a nutty suggestion but maybe you could record it on something and post an mpeg here. I'd like to hear what it sounds like.

VF

[moondog]

I haven't seen any mention of the timing chain. If the timing chain tensioner is not doing its job then the chain is lose and making a racket.

I don't know if it is the same on the K100 as the K1100.

The tensioner is operated by oil pressure and with the revs come up so does the tensioner and tightens up the chain. Another thought to think about when at hi-revs, the rattle goes away. I have read about the oil port that powers the tensioner can get clogged over time and reduce its effectiviness.

I also think some of the rattle can be just the nature of the beast. I hear the K75 is smoother. I know my K1100 is rattlely but have heard others and they all rattle to a certain degree.

[Dennie]

I'm in no hurry. When ever you get around to looking will be fine.


Thanks


Richard

just got in, will look first thing tomorrow afternoon. (I have a spare engine on the bench)

[hhshort]

Just because it could be too simple. Check the exhaust system for lose components. My k100rs sidecar tug has made death noises that were loose header pipes. Harold In Kansas

[Dennie]

I'm just going to (try) to add a few pics to IBMWR.org's tech. piece. it covers it real well. read here first: http://www.ibmwr.org/ktech/output-shaft-diagnosis.shtml
then remove this here part-

[Dennie]

then look here, you'll have to turn the engine to see all rivets- remember, they may look tight, but could be loose. the only way I know to tell is disassemble :bolt but you can still look though.

[Dennie]

you should see this-

[Dennie]

I haven't seen any mention of the timing chain. If the timing chain tensioner is not doing its job then the chain is lose and making a racket.

I don't know if it is the same on the K100 as the K1100.

The tensioner is operated by oil pressure and with the revs come up so does the tensioner and tightens up the chain. Another thought to think about when at hi-revs, the rattle goes away. I have read about the oil port that powers the tensioner can get clogged over time and reduce its effectiviness.

I also think some of the rattle can be just the nature of the beast. I hear the K75 is smoother. I know my K1100 is rattlely but have heard others and they all rattle to a certain degree. thats true, my tensioner piston had a broken plastic "nozzle" inside, and I replaced the whole bit and my idle rattle reduced somewhat.

[RICHO2006]

Hello Dennie,

Thanks for the pictures.

Next time I have the fairing off I'll remove the cover and check the condition of the rivets.


Regards


Richard

[Dennie]

dont forget IBMWR's website:thumb