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Hello everyone! I'm new to the forum today! The info. on here is so fantastic and everyne so helpful that I envisage riding a flying brick round the clock a few times, with the help of some TLC and a ton of help from all the knowledgeable old hands on here! But first I need to get hold of one...

So here's the thing:

I live in Derby, UK and I recently bid on an '85 K100RT on eBay and won. I went to see the bike and--long story short--there were a couple of problems that the seller has agreed to sort before I pay.

The only thing that really worries me though is a knocking/clunking noise that the engine makes when idling. I found a video of what sounds like an identical problem here:

http://youtu.be/o_vcGrSEu_Y

These things never sound exactly the same on recordings but the way it sounds is like someone letting a hammer drop a few inches under its own weight into the inside of the engine (I didn't identify exactly where it was coming from). And--as in the video--the engine speed slows a little before picking up again, occasionally slowing so much it sounds like it might cut out. It rides fine, no roughness at higher revs.

There's a post from 8-0ct-2007 called '85 K100RT Engine Nose...' by a chap called Brahma and I wonder if it could be ye same problem??? A user named 54089093 said in Brahma's post:

"The riveted (not pop-riveted) device referred to is the steel gear on the engine output shaft. As mileage gets hgh on the older bikes this gear and it's rivets loosen, leading to a knocking sound at idle, particularly when the engine is cold. If this is found to be the real source of noise, the output shaft should be replaced . This part was improved as of about 1989-1990 and if you examine the two side by side you'll see that the later part has more and larger rivets."

Is it likely that this is the problem? And if so I'm guessing I shouldn't fork out the equivalent of $1200 for the damn thing..

I'd really appreciate any advice here as otherwise this bike seems well cared for and a great deal. Thanks in advance for your help!!
 

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Sounds to me like either the ignition or F.I. is momentarily screwing up. Maybe an injector malfunction, maybe a spark plug/wire malfunction. A good dose of injector cleaner (Techron), some new plugs and a good throttle synch should improve that. How many mi/km on the engine? If the rivets shear, you will not have any drive at all, I suspect. I don't know if on the centerstand, in different gears (engine off) you could tell anything by moving the rear wheel to the stops, back and forth, and listen up front for any noise.

My original '85 K100 engine ran for well over 100,000 miles with no problems at all.

Frank
 

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Thanks for the reply duck bubbles!

It's funny that you mention the FI because the other main problem was that the bike suddenly wouldn't start (even though it started first time from stone cold when I went to see it) and it was also very sluggish when the revs were raised from idle--although it soon catches up--so I was wondering if this might be a problem with the fuel injector.

So maybe the problems are linked. It may have been sitting a while so perhaps it could even be as simple as a battery problem?? When failing to start all the warning lights do all light up as you press the starter button but I thought this might be normal? Either way I thought that a bit of tinkering would sort out starting problems and the slughish response on the throttle, given that it ran fine on test drive...

The clock is showing just under 70,000 miles, but I can't confirm this with the paperwork.

I've read that the final drive shaft rivets don't always shear off before they cause a problem, they can just be loose. What I wasn't sure about is whether free play caused by loose rivets could cause a 'knock followed by a stumble' problem like the one in the video. They're certainly isn't a horrible buzz/rattle as if the rivets have actually fallen off.

It's a shame the bike is stored a fair way away, I'd love to have another look now to see if I can figure out what's going on!

Any more more suggestions about what this could be would be very welcome! Just so I have an idea about what I might be getting into...
 

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It is normal for the warning lights to come on with turning on the key, not when you hit the starter.

Frank
 

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Discussion Starter #5
.

Didn't get this bike in the end, had some problems when I went to collect so I decided to call it a day and keep looking.

I'll be back with a brick of my own though..

Thanks for the help Frank
 

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These bikes are 30 years old+ in a lot of cases. There is no telling what a previous owner did or didn't do in many cases. I suppose I am lucky in that I bought my K new 30+ years ago and have done the maintenance myself. It is better to pass up a bike that doesn't give you a good feeling.

Frank
 

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My '85 probably has the same knock and intermittent miss. Drove me crazy. Had the TBs off and did a good synch, but discovered a hole in the intake elbow and replaced that. Kbike said MUST have zero intake leaks to idle well. Pre-replacement of the elbow, under light load (only) the miss would only happen below about 2000rpm and since I ride in rush hour traffic it was really aggravating.

You or the seller are looking, IMNSHO, at a tuneup to ensure all is correct. I don't think you're driveline is going to fail but I am thousands of miles away.with no money on the table.

One significant clue that I haven't been able to track, and that you should look for is that when the miss happens, the neutral light also flickers. This evidences a general electrical intermittent, NOT impending drive line failure. Strongly recommend you look for this on the bike, and consider your options, and what the present owner will do to compensate.
 
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