1989 K75 engine rattle/knock.

[Scott_]

Also makes for an opertune time to remove the arm and clean/lubricate the little baby roller bearings down in there.....

[gone_ape]

Just an update...got it all back together.....and.....as Led Zeppelin so notably proclaimed....The Song Remains the Same.....nothing changed...ALL THAT and there was zee-ro change in the bikes countenance of sound..Sorry Laitch, "No Movie Tonight"...I gave it the business and whatever this noise continues to be, I'm going to have to crack open the engine to really see......or not.

If it breaks, fine....it may never break and that's fine too.  I tried and came up snake eyes...but I did have fun, and isn't that what it's all about? 

[John Lang]

That's how my '87 K75 sounds, for the 50k km I have driven it. I thought it was meant to sound like that. Perhaps I am missing something. Old ears.

[The Mighty Gryphon]

Disappointed to hear that you weren't able to cure the noise in your engine.  As far as mine, I am able to report that after putting over 6000 miles on her in the past 2 weeks including a 24 hour flogging at 75+ the clank I had is still gone and the engine runs smoother than ever. 

There is a very slight knock that occasionally occurs at cruising speed(70+) when the engine is hot and the bike has beeen running for a couple of hours, but it comes and goes and doesn't have any effect on the operation of the engine.  I am suspecting the bearing for the alternator drive.  It was a bit questionable when I had the engine apart last winter, but didn't seem to be bad enough to warrant the cost of replacement.  I am beginning to think that with the speeds these engines run at, every bearing has to be perfect to keep things sounding nice and quiet.

[daveson]

Hi, gone_ape.
Output shaft endfloat is another check to make next time you do a spline lube. Probably need a dial gauge though. If the thinnest blade of a feeler gauge fits between the circlip and bearing, with outward pressure on the shaft, that's a problem, there should be no gap.

Hi K1300S,
  That's a good video you posted. Next spline lube, if the circlip end gap is bigger, or less engaged, on your noisy brick than the other, that might be another hint as to the cause of the knock, due to a fatigued circlip.

The circlip is cupped, so also acts as a diaphragm spring, to bind the gear hub to the bearing. These parts are about 30 years old now, so not surprising if it loses a bit of tension.

The K75 has minimal resistance to endfloat,  compared with the K100.

Unlike the k100, the power flow through the k75 does not go through the output shaft, so it's main job, other than doubling as a balance shaft, is to drive the pump. Since the output shaft isn't splined, that might be the reason the clutch nut torque is higher on the K75 than the K100. In ft/lb the torque is:
K75  ~100,
K100  ~75
That makes it easy to remember.

[Laitch]

Unlike the k100, the power flow through the k75 does not go through the output shaft, so it's main job, other than doubling as a balance shaft, is to drive the pump. Since the output shaft isn't splined, that might be the reason the clutch nut torque is higher on the K75 than the

Power is transferred to the output shaft of the K75 by the same means as the K100 uses. The main job of the K75's output shaft is the same as that of the K100's output shaft—the transfer of power from the engine to the transmission. See red arrows in the attached diagrams indicating power engagement. The significant differences between the two shafts are the balance weights of the K75's output shaft (green arrows in the diagram, the rearward weight having notches that engage with pins on the gear wheel), and the damper assembly of the K100 output shaft (blue arrow). Both output shafts engage with their respective clutch housing shafts by using splines—splines in the bore of the K75's gear wheel that engage with external splines on its clutch housing shaft; the splines on the output shaft of the K100 that engage with internal splines in the bore of its clutch housing shaft.

Another difference in fastener torque value is that the K100's value is developed by two steps: tighten to ~103 ft.lb., loosen, then tighten to ~73 ft.lb.; the K75's is developed by one step—tighten to ~103 ft.lb..

K75 output shaft.


K100 output shaft

[daveson]

To me it's looking like the power flow goes straight from the gear to the clutch basket. Anyway spose I've crammed too much in there cause the point I'm wanting to make is that anyone who has a knocking sound could check for output shaft end float. It would be a simple check when doing a spline lube. If there is any end float at all, that could result in knocking.

Need a dial gauge though.

[Laitch]

To me it's looking like the power flow goes straight from the gear to the clutch basket.

Power is transmitted from the crankshaft gear to the output shaft gear then into the clutch housing via its shaft; it's the same in both models. That's why those are called output shafts. Because the original post and subsequent posts are over three years old—except yours and mine—it's probably all over but the shouting. 

[daveson]

The sneaky little K75 has splines from the gear to the clutch hub. The K75 output shaft has no splines.

I'll say it's a non urgent fix, and that gone_ape is one of many who have just got used to it, probably still going now just the same.

Have you ever met a man who had a motorcycle with an output shaft that had no splines?

[Laitch]

Have you ever met a man who had a motorcycle with an output shaft that had no splines?

That would be you, daveson, virtually. 

[daveson]

Have a look, yes you have no radials and no splines.

Well except for the name's, and a few other changes,
When you talk about me,
The story's the same one.

[Laitch]

Your story is the same one, yep,
No radials, no splines.
But you don't need a dial gauge
To read between the lines

[daveson]

Good one, you could make a song out of that.

[daveson]

A few more thought bubbles. The clutch nut might lose some of its ability as a lock nut, again considering it's age.

If the rattle is worse on acceleration, maybe that's to do with the straight cut gears  in the intermediate housing, like on the auxiliary shaft, or the idler spring.

Also you want to be confident about the clutch balance marks, there was a recent case with an unbalance that produced noise more so than vibration (OK its a long shot but an easy check)

[@uldy]

Hi All
Long time between drinks on this topic.

I have a 1992 K75RT with 70,000km on the clock and am experiencing this knocking noise only between 3,500 and 3,700rpm. I thought the motor was going to hand grenade itself when I first heard it. You can accelerate to redline and won’t hear it, only sitting at the nominated revs in any gear.

I have the alternator out at the moment as many have said check the monkey nuts. The appear fine and if I didn’t know better would say they have been previously replaced.

The bike was purchased as a non running project and is now NSW Club registered. I have read many previous ideas relating to this noise (which sounds like a bucket of bolts) and many have stated removing the alternator stops the noise.

I may try this and if the noise disappears, consider spacing back the alternator to reduce any preload on the alternator shaft.

Not keen to pull the box yet 😩😵‍💫

[The Mighty Gryphon]

I had posted a photo on this back in 2016, but it seems to have disappeared.  Here it is again to show what the problem was on my bike.  It appears that the power pulses are uneven enough at some rpm to cause acceleration/deceleration of the output shaft to be bad enough to make the tabs rattle in the slots.


DSCN1758.JPG (46.82 kB . 768x576 - viewed 552 times)

Tightening the clutch nut cured the problem for a year or so, but the noise came back.  I think that if I go back in there again, I'll put a bit of Loctite bearing lock on the face of the clutch hub to see if that will keep things together for a longer time.  In the meantime, I have found that getting the valve clearances as close to the same as possible and balancing the throttle bodies helps a little.

[@uldy]

Thanks, The Mighty Gryphon.
I had read all the previous threads and was curious if there had been any further development in the field or with owners.
I have also backed off the threaded bolt clutch adjustment underneath the bike, this in turn has changed the tone of the backlash noise when rocking the wheel back and forth in gear.

Clutch operation appears ok in the garage.

Too much rain in Sydney at the moment for a decent test ride.

[daveson]

Since you have the alternator removed, has the noise now disappeared? If yes, it might also be the alternator itself, does it spin perfectly?

Can you post a video of the backlash noise, and the noise at 3,600rpm?

At 3,600rpm, with the clutch pulled in, does the noise disappear, change, or remain the same?

I spose not, but do you hear a loud, distinct  clunk after the engine stops?

[Laitch]

I have also backed off the threaded bolt clutch adjustment underneath the bike, this in turn has changed the tone of the backlash noise when rocking the wheel back and forth in gear.

Usually backing off that bolt on a properly adjusted clutch will interfere with smooth shifting sooner than later. Your field trial could be informative. Are you certain that rattle isn't coming from the timing chain? There's an article at IBMWR written by a Brick owner that chased, caught and defeated a rattle that had been a bother for 10 years. He might have won the coconut for Persistence.

Thanks to many videos and posts from Brick owners over the years, I've learned which rattles are benign—most of them. I've accepted my Brick's occasional imitation of a TR3 because it's more comfortable than a TR3. 

[daveson]

True. Before we assume the worst, can you pinpoint the exact location of the noise, and does another pair of ears agree? I'll guess the noise with the engine off is unrelated and not very important.

[@uldy]

Hi All
Thanks to all for your comments and input
After reading many threads on this subject and my own riding and mechanical experience, in this particular instance I feel The Mighty Gryphon is on the money.
When I initially discovered this noise it sounded to me to be coming from the top of the motor. It was difficult to diagnose as with the RT Fairing the noise tends to amplify around. If I was a betting man I would have initially said timing chain, however, with different throttle inputs the noise was too inconsistent. You could accelerate briskly towards redline and no noise was evident which to me ruled out timing chain. If you kept the revs between 3,500rpm and 3,700rpm it sounded like a bucket of bolts whilst maintaining a light throttle load. If you backed off or floated the throttle (no load or over run) the noise would stop.

I agree with the theory the noise is a power pulse or harmonic produced by the motor on a light throttle in the nominated rev range. I also agree that the noise is probably generated from the balance shaft tab area. Trying to rectify the amplified noise being generated is the issue.

I have had my alternator out and the monkey nuts appear to be in a very good condition, spinning or turning the alternator by hand is as smooth as silk, there are no tight spots or noise evident.

As some members have previously mentioned their noise was no longer evident with the alternator removed, so I focussed my attention that the alternator when fitted must be pre loading the the drive shaft and contributing to the noise generation. I then glued three flat washers, one on each alternator inside mounting point to release some preload off the alternator drive shaft when the alternator is fitted.

As previously mentioned I have backed off the clutch adjustment bolt underneath to the point where it just touches, This resulted in the arm striking the muffler. Today I carefully reshaped the top of the muffler allowing clearance for the clutch arm. I then adjusted the free play at the lever.

On a short road test today, I would say at least 75 percent of the noise is gone. When I arrived home I removed the alternator and placed an additional washer on the inside mounting points, this equates to a two millimetre thickness spacing which in turn I hope will remove any preload on the alternator drive shaft and hopefully not cause any abnormal or premature wear on the monkey nuts.

Reassembly and test ride tomorrow, fingers crossed 🤞👍🍻

[daveson]

???

Any updates.

If you're interested in a little experiment, here's one. After removing the crank cover, you might have two small windows of access to the area where the tabs are (at least the k100 pictured does) Clean it, let it dry, paint it, let it dry, a small circle of paint between the tab and the slot. If you still have the noise problem and the paint hasn't cracked, the tabs haven't moved. Or maybe better a dab of paint in the gap.

Or someone else with the problem might want to run the test. Hmm. Maybe.

[@uldy]

Hi All
Apologies for the delay in reply, probably fallen into depression.

Took the bike for a long ride to get it nice and warm, unfortunately the noise is still evident, slightly reduced but evident.
Im just disappointed, such a great bike and a minor mechanical glitch makes it so frustrating.

I will probably just ride it as is at the moment, I do have the time but certainly not the patience to remove the gearbox and replace/torque the clutch nut as has been mentioned previously.

Cheers
Auldy

[Laitch]

Gryph seems to have gotten positive results though with his cleaning-torquing technique. If I outlive this clutch disk, I'll pay closer attention when I—or my nursing assistant—replace it.

As luck would have it, I did outlive the clutch disk because it became oil soaked from running with a leaking engine output shaft o-ring for ≈10,000 miles. Not only did I replace the clutch disk, I also installed new clutch pack screws, new clutch pack screw washers, a new compression ring and a new clutch nut. A byproduct of the procedure was the elimination of rattle at idle in neutral with the clutch hand lever not pulled—the rattle that might be the source of @uldy's transient Brick-quality despair. Does this mean @auldy should replace those parts to find peace? To quote Joe Kenda, "Maybe."

I'll update this thread with the date, time, place, social circumstances and what I was wearing at the moment if the rattle resumes. If it hasn't been heard for 12,000 miles more, I'll post the news if such a benign sound manages to penetrate my state of equilibrium among rattles.

[The Mighty Gryphon]

The rattle came back on my K75 a couple years later and has been there since.  It appears the torque works to stop it, but is only a temporary stopgap.  If I ever go back in there again I will try putting some Loctite, either Red or Bearing Lock on the face of the clutch hub to help reduce hold the contact faces from moving relative to each other. 

Will have to be careful not to get any Loctite on the clutch nut.  With the torque on it, that red Loctite will effectively weld the nut in place.