1991 K100RS - Rattle when accelerating - K-Bikes.com - Excellence in Motion
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post #1 of 5 (permalink) Old Jul 16th, 2013, 6:38 pm Thread Starter
Join Date: Jul 2013
Location: Seattle, WA, USA
Posts: 2
1991 K100RS - Rattle when accelerating

Hi All - new guy here. I have a '91 K100RS 16V with about 60,000 miles on it. I've had it 2 years and put about 10K on it in that time. Since I've owned it it has always made this rattling noise at low RPM while accelerating or decelerating. It idles fine and does not make the noise at any other time.

I did some research and found another thread on here that sounds exactly like my problem:


I already checked and replaced the rubber buffers in the alternator. Not the problem.

I am going to try and capture the sound in a video which I will post a link to, but would appreciate any ideas on what it might be. I know these K bikes are notorious for rattles, but I don't think this is the normal K rattle.

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post #2 of 5 (permalink) Old Jul 16th, 2013, 10:53 pm
PsyKotic Waterfowl
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post #3 of 5 (permalink) Old Jul 17th, 2013, 6:13 am
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Location: , , UK
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Hi, I can only offer you 'generic' pointers as I have the K12.

Even on the K12 with its notorious box O rocks idle rattle (that's caused by the intermediate crank gear slopping about), rattles under power should not be there.

That is because the intermediate gear is under load and the cam chain should be running nice and tight. Of course, if the cam chain tensioner is not working or the guides are worn then you could get rattles under load.

I don't want to worry you, but I had this problem once on a car engine and it was caused by low oil pressure. Although you have an oil pressure warning light, it only comes on at around 7-10psi. You would need to temporarily find a way to attach a gauge and check you are getting around the 80 psi oil pressure at 2K rpm.

Another issue might be pre-ignition or 'pinking' under load which happens when a motor is timed too advanced for the fuel it is using. There are many new lower octane fuels around now and with an older bike may need to consider retarding its timing a degree or so if it is still at the oem setting. If you find the idle is not stable and fluctuating, this could be the cause.

Another cause of rattle under load is top end piston bearings and/or lubrication issues, a similar thing is an oil pump at low pressure gets less oil to the valve and cam gear.

Don't get paranoid, but do check the oil presure first.

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post #4 of 5 (permalink) Old Jul 18th, 2013, 1:53 pm Thread Starter
Join Date: Jul 2013
Location: Seattle, WA, USA
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Thanks for the tips! I'm pretty sure its not that heat shield, but will check it out for sure.

Will also check out the oil pressure and take a peek at the tensioner / guides. Never looked under that cover before.

Will post back with results.

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post #5 of 5 (permalink) Old Jul 28th, 2013, 4:26 pm
pipeandslippers's Avatar
Join Date: Aug 2012
Location: london, london, uk
Posts: 20
Is it possible your brake disc bobbins need to be replaced?
This has always been the source of rattles on my 16v k100rs.
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