Friend of mine asked me about his noisy 85 K100.  He thought it was the bottom end (right side ) but I suggested that it might be the output shaft since I'm vaguely familiar with that issue. It seems that that is his problem.

What happens if you just ignore it?

Although I've heard of this issue I've never had to deal with it.  What are possible solutions? Replace with a later 12 rivet output shaft, correct?

Replacing it with a 12 rivet shaft is the usual option. They usually get louder and louder and sometimes the rivets shear. One of the guys here redrilled the holes midway and replaced the rivets with bolts, I think that shaft is in the engine Charlie has for the red frame monster and is yet to fire a shot.

My 86 k100 with 180k on it has the same issue.  Chris at the BM shop in Brisbane said "start it and keep the revs up where it makes little noise and go, don't let it sit there and warm up".

For me, it is on the to do list after the young girl (12k) is back together.

we did that bolt mod output shaft basket swap over to Gerty in 2014 rick , keep in mind  I didn't have new barrel rubbers to replace so the old ones so  the old ones went back in with some slight rotational movement.

I think Gertys output shaft basket is making some noises again now  and as soon as I can get the red frame bike on the road ( with replacement output shaft basket - care of smithy ) I will be replacing gertys again for one I picked up from grahame jays (bega) which is still in good condition.

i'm convinced that as the output shaft barrel rubbers harden up and shrink a little , the slight movement it creates both rotationally and laterally assists  in the rivet wear . in addition to low idle revs.

when rebuilding the red frame motor I installed new barrel rubbers , which were a significantly tighter fit to the barrel and output shaft vanes .


ill post pics of the bolt mod after I get it pulled apart ,  im guessing the bolt mod has been in place 100,000 klms or more by now , with many thanks to Alby .



edit

that's interesting tesla . when I spoke to chris in 2014 he claimed he had never heard of the issue before , and looked at me in a very strange way , disbelievingly in fact .

oh well , we all learn something new , along the path

I think Chris says what he thinks people want to hear!  He said he'd done a number of them but they are just not economic as if you're taking of the transmission etc you should do the clutch and rear main seal and given the water / oil pump is being removed this should also be rebuilt.  That's along the lines of what he said to me along with the "start it and ride away".

I'm the friend that Duck mentions at the top of this thread. The bike is an '85 K100RS with about 80k miles on it (broken odometer, of course). I rescued it from a young woman in Santa Cruz California who had dropped it so many times the duct tape holding the mirrors on was an inch thick. The bike sat out in the weather for two years and needed attention. I took it off her hands for $150US, cleaned it up and turned it into a somewhat presentable naked bike (from a distance... if you squint).

It's something of a relief that the engine noise I'm hearing is an output shaft issue rather than a crankshaft problem as I had originally suspected. And yet it's kind of unbelievable that the engine could have gone into production with such a potentially expensive flaw. I wonder if the engineers were the same ones who crashed that space probe into Mars.

Has anyone experienced or seen the result of the output shaft rivets failing or wearing out completely? Is there some sort of catastrophic bang at some point? Or does the noise simply get louder and the drum hammers away until it wears out the drive gear? I imagine all of the rivets might shear off and the drum would still stay relatively in place. But then you'd have rivet shards in your oil and that's less than desirable. And what is the best way to locate a good used 12-rivet shaft, anyway, when everyone else with a 6-rivet motor is searching for one?

I've only just got the bike back into riding condition this weekend so I plan to put a few miles on it while I contemplate how/whether to address the noise.

Many thanks in advance for any insights, advice, suggestions, insults, etc.

My Ks have 6 rivet shafts in, RT has about 90k miles, the 'new' RS has just under 30k miles having sat in a boat shed for 17 years with very little use.

I just change oil and will deal with it if it becomes an issue in either.

My thought is leave everything and then go in at some point and do the lot.

Scroll down to the Time for the engine inspection section of this renovation photo essay to learn about  another output shaft noisemaker.

How about posting a YouTube recording of the sound?

Temporary solution dept:

Given the princely sum you paid for the bike...

I replaced a 6 rivet with a 12 rivet
While I was looking at the 6 rivet one, there indeed was a little 2mm?? play...we'll assume was the cause of the noise.

Being a tight arse, I decided to get a big flat punch firmly held in a vice and another big punch (end is tapered) , pound hammer and ubiquitous reluctant assistant (13 year old son) and gave each of the rivets a "good whack". One side of the rivet is flat the other has a hole... all quite obvious)

There is no play - the rivets now widened. One day, if desperate, I might use it. 

Not sure how long it will last. Optimistically, the output shaft can't be likely to immediately regress into play (surely the rivets will be much the same as before and any widening of the space around the rivet in the shaft is now filled with squashed rivet).

Here's hoping

Make sure some decent loctite is used around the outside edges of the two big bearings to stop them moving in the lower engine block (there is a special word for this - Laitch or Duck will oblige...spalling, fretting??) - I had some wear in mine).

You could have this done in a day... or years - other K bikes might when appear in driveway in the mean time.

Guy