K75 Engine noise

[The Mighty Gryphon]

  Great!!!   Now, please go out to ride and enjoy the hell out of your bike.  Learn to ignore the noises and concentrate on having a good time.  You have a beautiful bike that can bring you many years of enjoyment.

[bgcameron]

From your post, it appears like you did nothing to the nut because the nut seemed tight. Maybe the cure was just the laying on of hands. I've seen that work miracles in venues as disparate as fundamentalist churches and South Dade honkey-tonks. 

I forgot to mention that I replaced the nut and o-ring while I was in there. I gave the new nut just over 100ft lbs of torque.

[The Mighty Gryphon]

I forgot to mention that I replaced the nut and o-ring while I was in there. I gave the new nut just over 100ft lbs of torque.

Okay, if you go back to post #49 in this thread and look at the photo, you will see that the two parts are pulled together by the clutch nut.  When you tightened it, you increased the pressure holding the faces together so they are more difficult to move relative to each other and make the tang clank in the slot.

It's nice that you have reduced the noise, but be aware that some time in the future, the friction between those parts will decrease enough to allow your noise to return.  I hope that by that time you are able to ignore it and just ride the bike.  It won't hurt anything.

[bgcameron]

Well, hopefully it doesn't return. Perhaps that wasn't even the issue at all.

I could not accept a clatter as loud as what my bike had. Hard for me to ignore.

[daveson]

Bonus, good work.

I'll also guess the clutch nut is on a little tighter, a nut on a bit under 100 might not move cause it takes a bit more to get going. 

So it's not eliminated but way better, good. The next rider with these symptoms who is removing the clutch basket has an easy opportunity to see if replacing the circlip eliminates the problem.

Gryph help me out here, the balance shaft isn't doing much more than driving the pump, could the forces overcome 100 ft/lb on the clutch nut? And if so, why don't all k75's do it? And at 3,500 rpm?  And the machine marks are still on yours? I'll have to say this again, I'm not a mechanic and this is over my head, but I think a new circlip MIGHT solve it, and it's easy to get to. I hope this doesn't come across as pushy, just trying to get to the bottom of it.

I spose someone will give the circlip a try in the future.

Branden, just curious, the clamped cuts in the old clutch nut, I spose they were closed?

[The Mighty Gryphon]

You WILL have the noise return if tightening the nut corrected it.  If it bothered you that much, I would advise putting the bike up for sale now before it returns.  Waiting until the noise comes back will only lower the final sale price and make the bike harder to sell.

[daveson]

Tightening the nut partially corrected it.

I think the clutch nut and circlip both contribute to eliminating endfloat. Let's look at the drawing and imagine the circlip totally fatigued, not just partially. It is so fatigued that there is a gap, between the circlip and bearing, even with the engine stopped. That would be worse again, possibly with a knock at all rev ranges. In that case you would still have a knock even with the clutch nut at 150 ft/lb.

On the occasion that the noise remained after pulling the clutch in, until it got to 20km/h, that again points to the circlip, I think. Pulling the clutch in compresses an already weakened circlip. In the video I think I hear the noise momentarily between gears when the clutch is pulled in. That was why I asked earlier about pulling the clutch without disengaging it, since it only happened under load.

There's a service bulletin relating to the earlier version about output shaft noise, due to, amongst other things, a loss of pressure applied by an idler gear diaphragm spring. The minimum action recommended, was that it be replaced. In the newer version, it's replaced with shims, pressure is applied on the bearing by the circlip. That also makes me think that replacing the circlip could be a fix, and can be replaced without splitting the engine, so that's one good thing. 

[bgcameron]

Bonus, good work.

I'll also guess the clutch nut is on a little tighter, a nut on a bit under 100 might not move cause it takes a bit more to get going. 

So it's not eliminated but way better, good. The next rider with these symptoms who is removing the clutch basket has an easy opportunity to see if replacing the circlip eliminates the problem.

Gryph help me out here, the balance shaft isn't doing much more than driving the pump, could the forces overcome 100 ft/lb on the clutch nut? And if so, why don't all k75's do it? And at 3,500 rpm?  And the machine marks are still on yours? I'll have to say this again, I'm not a mechanic and this is over my head, but I think a new circlip MIGHT solve it, and it's easy to get to. I hope this doesn't come across as pushy, just trying to get to the bottom of it.

I spose someone will give the circlip a try in the future.

Branden, just curious, the clamped cuts in the old clutch nut, I spose they were closed?

Yes, they were closed.

Perhaps the noise wasn't caused by the clutch nut at all. As Laitch said, "laying hands on it".. perhaps there is something between the engine and the rear wheel that tends to get cocked somehow and it gets fixed in the process of a simple spline lube.

Gryph, I may be a little OCD but I am not a defeatist. It would be silly for me to sell such a gem of a bike. These machines are rare around here and I've got enough mechanical aptitude to keep it running. Did you listen to my last two recordings of the noise? I was really hoping you would chime in and let us know if this is similar to what your bike was doing.

Throughout this process of the teardown there is a tool that I borrowed from the 30-year/370,000 km K75 owner that was extremely helpful. He took scissor jack and welded a plate to match the holes on the bottom of the gearbox where the center stand attaches. There are a couple of skids on the bottom to keep it from tipping over. This made removal and installation of the gearbox incredibly easy!

[daveson]

Rather than looking at a k100 drawing, and imagining the differences for a k75, here is a k75 drawing. Again, not to scale or exact, just to help visualize it.

[daveson]

Just adding a post to this old thread cause I have since read about three other problems similar to this, where the noise was related to the alternator. It could be the alternator, but more likely the rubber dampers between the alternator and the engine. They could have shrunk and/or hardened. It's an easy check. Since the dampers are about thirty years old, this noise could be the result even though this brick is in top condition and only has minimal mileage on it.