Balance shaft noise

[The Mighty Gryphon]

After two years of listening to my K75RT clatter and clank between 1200 and 2000 rpm I decided to break down the engine to fix the source of the noise that I was sure was a loose idler gear on the output shaft. 

Today I pulled the output shaft out and found to my chagrin that the idler/anti-backlash gear was nice and tight.  It couldn't possibly be the source of the noise.  So I started checking everything in the intermediate section and nothing could possibly be the source of all that noise.

Then I stuck the balance shaft into the hole in the output gear and noticed there is about 30-40 thousandths clearance between the tangs on the gear and the notch on the balance shaft.  When the shaft is rotated it makes a solid mechanical tap sound not unlike what I hear when the engine is fast idling or starting out in first gear.   

Is this the way these parts are supposed to fit???  Is there something missing that closes the gap and prevents the parts banging against each other?   Does anyone know what the correct fix is? 

I am thinking of having some weld bead deposited on the sides of the balance shaft grooves and filing for a good fit.   Will that hurt anything?  Never saw anyone else have this problem, or isn't it?

[Laitch]

Is this the way these parts are supposed to fit???  Is there something missing that closes the gap and prevents the parts banging against each other?

It sure looks like wear is occurring on the mid to lower side of the tang and near its joint along the base. Good photo, Gryph. Besides the rhythmic tapping at idle (a feature I find appealing when not potentially lethal to the engine), what effect might that lash have on other parts of the assembly?

[Martin]

+1 Laitch looks like wear to me, you could weld it and file down, but you would have to be careful not to effect the hardness of the part you are welding.How many miles has it done?
Regards Martin.

[The Mighty Gryphon]

Bike has 77k on it.  It has been making that noise since I got it with 53K.  What is puzzling is that I cannot see any wear.  The parts were machined that way.   

Has anyone else seen this gap in their engine?   Is it supposed to be there.  I have been looking, and can't find an answer.  If not the tangs, what keeps the balancer shaft from floating around in relation to the gear and making all that noise? 

Is it the torque on the clutch nut pulling the shaft to the clutch basket which is held to the gear by it's splines?  It's the only thing I can see.

[K1300S]

I have not taken mine apart,  but my k75 makes the same rattle from 1200-2000rpm when starting off.  Bike has about 35k miles on it.

[Laitch]

It has been making that noise since I got it with 53K.  What is puzzling is that I cannot see any wear.  The parts were machined that way.

Mine makes a rattle if it's lugged and has ever since I got it except I don't let it lug. I feed it revs. It's at 51K. If they were machined that way then, case closed—if you'll pardon the expression

[bocutter Ed]

Mine started to rattle last year. Prior two years didn't do dat.

[TrueAce]

Gryph, that gap seems to large to be factory spec, and there is no signs of wear on hard edges. Could the shaft have been previously replaced with one from a different series? 

[The Mighty Gryphon]

Update, I assembled the shaft on the bench.  It looks like the only thing that keeps the shaft from rattling is friction between the face of the clutch housing spline hub and the shoulder on the end of the output shaft.   I wonder what the coefficient of friction between the faces is with 100 ftlb of torque on the clutch nut(minus the drag on the self lock on the nut).  What is the inertia in the balance shaft at 2000 rpm? 

I am guessing that wear accumulates on the mating surface and eventually gets to the point where things can flop around pretty easily.  It appears that my motor has been apart before I bought it.  The clutch is marked and what looks like a new clutch o ring was on the shaft.  Wish I had checked the torque on the clutch nut before I took it off.  It was tight, but didn't feel like 100 ftlb. 

Anyone here actually seen this before and fixed it?

[F14CRAZY]

I was under the impression that K75's made this noise even when brand new

[The Mighty Gryphon]

My K75S and K100RS don't make the noise and I have seen a few other K75's that didn't make it either.  Makes the engine sound like a piece of crap when it's idling and starting from a stop.   I really don't like the idea of having gone so far and not really found anything I can correct.  Three days to get to this point and three or four to get it back together.  Don't ever want to do this again on this bike.

[Laitch]

Mine started to rattle last year. Prior two years didn't do dat.

What was the mileage before and after the rattle, Ed?

[bocutter Ed]

Guessing less than 50K miles. I could look it up tomorrow ...

[scotbotmosh]

I 86 K100 with around 82, 000 miles does the same thing. I just got it a few weeks ago and I've been wondering about this as well.

Sent from my Pixel 2 XL using Tapatalk

[The Mighty Gryphon]

The noise addressed in this thread is related to the balance shaft of the K75.  It does not relate to the K100.  On the K100 it is probably the anti-lash spring or the rivets on the output shaft.

[caveman]

TMG, did you ever get this sorted out? FWIW I have 2 92 75s's one with 33k the other with 146k and I have not noticed any rattle noise. Could it be the RTs have a different arrangement?

[The Mighty Gryphon]

Not sure why some get it and some don't.  My RT is still pretty quiet, but the K75S which is coming up on 42,000 miles is getting a rumble between 1200 and 2000 rpm. 

Knowing that the clank just makes the bike sound like a piece of crap and doesn't hurt anything, I'll just let it go until I have to go into the clutch for the o-ring or the rear main seal.