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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: jsngrimm on March 04, 2018, 06:53:22 PM

Title: Odd sounds from an '87 K100RS
Post by: jsngrimm on March 04, 2018, 06:53:22 PM

My '87 K100RS with about 50K miles has been making a few odd sounds since I got it, and I think I know what they all are, just wanted to get more opinions.

First: When the bike has been running/driving a while and heats up, there is a rattling sound near the right rear of the engine, seems to be coming from the alternator, I assume this is just alternator bushings, or possibly anti backlash spring? Only starts to happen when hot, and since I have an '87 it should not have the output shaft rivet issue correct?

Second: Also starts when the engine is hot, at the left front of the front of the engine/timing cover. Rhythmic kind of rattling sound, like a chain running on a sprocket. I assume this is just slack in the timing chain and it needs to be replaced/tensioner cleaned?

And finally this which I am 99% sure is just noisy fuel injectors, rhythmic tapping/clicking sound, changes with rpms, coming from the front left side of the motor when it's running. Valves do need a check but I assume there is a high chance that is all just noise from the dirty original injectors?

Any help is appreciated! This is my first BMW and first euro bike at all, so I'm still getting used to it!  :bmwsmile

Title: Re: Odd sounds from an '87 K100RS
Post by: Martin on March 04, 2018, 08:10:00 PM

The alternator drive has rubber dampers in them called monkey nuts and these can wear out. At 50,000 miles it would be unusual for timing chain wear but could be possible. It could also be a sticky tensioner. To determine where noises are coming from you can either purchase an automotive stethoscope or use a large screwdriver. Place the end of the screwdriver on the spot where you suspect the noise is emanating from and put your ear on the end of the handle. Move the screwdriver around until the noise is at it's loudest.
Regards Martin.

Title: Re: Odd sounds from an '87 K100RS
Post by: Martin on March 04, 2018, 08:13:49 PM

Harbour Freight $4.00 US Stethoscope. https://www.harborfreight.com/mechanics-stethoscope-63296.html
Regards Martin.

Title: Re: Odd sounds from an '87 K100RS
Post by: Laitch on March 04, 2018, 11:31:41 PM

Quote from: jsngrimm on March 04, 2018, 06:53:22 PM

I assume this is just alternator bushings, or possibly anti backlash spring? 
I assume this is just slack in the timing chain and it needs to be replaced/tensioner cleaned?
I assume there is a high chance that is all just noise from the dirty original injectors?

I can't hear anything wrong.  :yes