Unusual noise K75

[seahorse]

I have copied this from another forum as I have something similar;

A bit of a conundrum this one, when riding my K75 RT under load in any gear, I have a sort of clacking/knocking sound towards the front of the bike (but it could be anywhere as the fairing could amplify it) it only does this between 3,300 and 3,800 RPM, I have run the bike in all gears on the stand at this rev range and above and below, and no noise, I have renewed the alternator cush drive rubbers but the sound is still there, everything on the bike is fine as I've just spent a couple of days on giving it a full service, spline lube, throttle body sync, TPS etc but this noise persists ! I'm sure it's not the output shaft rivets as this would create a buzzing sound not clacking/knocking noise, all I can think it can be is the timing chain, but why only at this rev range and under load ? Have any of our members ever had this problem or have any ideas ? I've searched all the BMW K Series Forums on the net but to no avail.
Thanks in advance,
Clive.

 

[seahorse]

And my own response;

Mine does this as well. I find that it is only under fairly light load, more throttle and it goes away. It is definitely engine speed related as it does it in any gear. I am thinking either output shaft broken backlash spring or possibly something in the alternator drive. By this I mean bearing, not the rubbers. I would not describe mine as coming from the front of the bike though. I think it is back of engine/gearbox area, and can sometimes feel something through the LH footrest.
I would love to find out the cause but It has been happening for I would guess 2 or 3 years. This is 20 or 30k and the bike is now on 103k! It has not got any worse so I have stopped worrying about it. Apart from yourself I have never heard of anyone with the same thing and I have posted before on other forums.

 

[Steptoe]

It could well be, and it's a big "COULD", the cam chain tensioner.

The small spring loaded twisty plunger that sits behind the front engine cover.

Remove from cover, undo the tensioner housing and remove. Take out the plunger and check the bottom, it breaks but still works, only it doesn't tension the chain as well as it should, hence the noise. . _ It's not a very common problem but i've seen a few bikes with it broken over the years, they make just the noise you describe.
Just make sure the noise is at the front engine cover.

 

[seahorse]

Thanks for that, may have a look when I get a chance. What is that breaks, the plunger itself?

 

[Steptoe]

Thanks for that, may have a look when I get a chance. What is that breaks, the plunger itself?

The small section inside the plunger, it has a round serated type piece on the bottom that locates in the housing.

 

[BenFranklinIII]

Hallo seahorse,

did you find a solution for your noise under load?

I think I have the same problem. Under load at low rpm I get a rattling sound. At 2500km at the latest it stops.

I would be thankful for any suggestions.

Best regards.

Benjamin