Author Topic: Clutch rattle - with a twist (Read 5780 times)

Skonnie Boy · « **on:** August 18, 2009, 07:06:43 AM »

I have what I believe to be a rather nasty clutch rattle on my 750K6. Only its not the annoying yet harmless rattle at idle, it happens when I downshift from 5th, 4th and sometimes 3rd. It only seems to happen after about 10-20 minutes of highway riding, when the engine is warmed up. I only recently noticed it, since taking an extended trip up north.

I recently changed the oil to 20W-50. Carbs have been recently synched and it runs nicely otherwise. It only happens when downshifting and disappears when I pull the clutch in. Since 95% of my driving is in the city, I hadn't noticed it. Any ideas?

Tower · « **Reply #1 on:** August 18, 2009, 09:11:19 AM »

Some possibilities...(in order of probability?)
1) Worn shifter and transmission parts sometimes rattle. Probability that this is the cause goes up, since you only experience the noise when in certain gears and only when shifting in one direction. Look for worn dogs and right shift fork: usually comes with hard shifting or difficulty staying in gear. If the noise is really load, look for excessive gear lash and bearing wear on mainshaft or countershaft: sometimes accompanied by whirring/whining sound.
2) Thick oil will actually reduce the amount of oil in the clutch assembly, especially around the outer clutch basket. Less oil means more rattle. Does the clutch smell of burned rubber/cork?
3) When engine heats up, the parts will as well, increaseing the tolerances in the basket. When downshifting from top gear, the engine would be revving at its highest RPM and the resulting harmonics might cause the rattle. As engine RPM reduces your specific harmonics disappear taking away the rattle. Balancing the clutch outer basket solves this problem.

mystic_1 · « **Reply #2 on:** August 18, 2009, 07:16:59 PM »

Is it a rattle, or is it more of a clatter, or perhaps a thunking?

Thicker oil means more drag so perhaps your transmission mainshaft is slowing it's rotation faster than usual when you pull in the clutch to downshift, so it's not in sync with the countershaft, and you get clatter from the engagement dogs?

Change the oil back to your previous viscosity and see if it changes anything. This also gives you a chance to inspect for foreign matter in the oil (metal flakes, filings, etc) which would be evidence of something more sinister.

mystic_1

Skonnie Boy · « **Reply #3 on:** August 18, 2009, 07:41:33 PM »

It verges on being clatter, like something is loose and rotating. I was able to hear it through my helmet.

I used to run 20W-50 when I lived in Austin, never had the problem there, though in truth I never took it on a long trip. In 2.5 years and 5K+ miles of city driving, I wouldn't be surprised if something clutch related needs attention. I've never fooled with the clutch or gears, but this might be as good a time as any to start.

Hush · « **Reply #4 on:** August 18, 2009, 11:56:20 PM »

Sounds like thinner oil might help.

Bowswell · « **Reply #5 on:** August 19, 2009, 10:08:59 AM »

http://data.sohc4.net/Clutch_rattle.jpg

Skonnie Boy · « **Reply #6 on:** August 19, 2009, 09:02:05 PM »

Most helpful. Just out of curiosity, how does one balance a clutch basket?

Tower · « **Reply #7 on:** August 20, 2009, 09:32:28 AM »

How to balance a clutch outer basket....
Lock it onto a lathe: Spin it very fast: Mark where it wobbles (like balancing a wheel): Drill away tiny amounts of metal on the fingers opposite the mark: Repeat.

Or buy one that is already balanced.

tlbranth · « **Reply #8 on:** August 20, 2009, 09:42:19 AM »

Quote

Lock it onto a lathe: Spin it very fast: Mark where it wobbles

Tower, sounds good. But how can you tell where the heavy side is?

Skonnie Boy · « **Reply #9 on:** August 20, 2009, 11:01:20 AM »

Pardon my ignorance, I'm guessing you are referring to the outer clutch basket? Which spins only when the clutch is engaged, i.e. not pulled in? Interesting stuff.

Not sure if I have the means to balance the clutch, though I may have a line on a spare.

Tower · « **Reply #10 on:** August 20, 2009, 02:00:49 PM »

With a steadied hand (e.g. using the cutter stand), move a crayon or chalk towards the spinning outer basket. The heavy side will wobble outward and will hit the crayon first - marking the heavy spot. The physics are similar in principle to how wheels are spin balanced.

This is bound to be dangerous, as the small diameter of the basket means you'd have to spin it fairly fast to get a sufficient amount of wobble. Kids, don't try this at home without a shield.

Hush · « **Reply #11 on:** August 20, 2009, 02:07:38 PM »

Or safety glasses eh Fuzzy!

Skonnie Boy · « **Reply #12 on:** August 27, 2009, 10:27:29 AM »

Its a miracle. A real, documented miracle.

I fixed my clutch rattle by tightening my chain. And then shortly after I did so, jebus or some other deity swept over my shoulder and made the clutch rattle disappear.

BELIEVE, people, BELIEVE.

Hush · « **Reply #13 on:** August 27, 2009, 12:27:16 PM »

So does that mean that the bearings on the shaft that runs from the drive sprocket through to the clutch is so knackered that tightening one side pulled in the other?

tlbranth · « **Reply #14 on:** August 27, 2009, 12:35:56 PM »

Quote

So does that mean that the bearings on the shaft that runs from the drive sprocket through to the clutch is so knackered that tightening one side pulled in the other?

Sorta sounds that way. I wouldn't regard it as fixed, mate.

Skonnie Boy · « **Reply #15 on:** August 27, 2009, 12:38:26 PM »

Yes. YES.

When I loosened the axle nut with the Holy 26mm socketwrench of Antioch, I could feel the clutch being rid of the rattle demon. Once the evil spirit left my clutch basket, it tightened right back up and works fine.

We Americans are nothing if not a spiritual people.

---------

The rattle I was hearing was the chain hitting the swingarm when I decelerated. It had about 2"+ of free play. Lesson learned.

tlbranth · « **Reply #16 on:** August 27, 2009, 12:44:29 PM »

Oops. Should've re-read the initial problem. I was thinking standard idle clutch-rattle. Glad you solved it.

Skonnie Boy · « **Reply #17 on:** August 27, 2009, 01:03:18 PM »

As am I. The stupid I feel is outweighed by the relief I feel over not having to replace or tear into my clutch. At least I have a spare clutch basket and plates now.

bert96 · « **Reply #18 on:** August 27, 2009, 05:06:25 PM »

Quote from: bowswell on August 19, 2009, 10:08:59 AM

http://data.sohc4.net/Clutch_rattle.jpg

I did this mod,it help a little bit.

Bert

Hush · « **Reply #19 on:** August 27, 2009, 05:14:50 PM »

I wish you'd fix her zip Bert, I've watched that a dozen times and she can't get it past halfway!

Don't worry Skonnie I have done worse, I bent the inner chain guard on such an angle the chain hit it every time it went past, thought I'd completely f*#ked my engine, felt real silly when my mechanic showed me what I dah done.

Tower · « **Reply #20 on:** August 28, 2009, 06:33:44 AM »

If tightening the chain really worked, then you didn't have clutch rattle to begin with - your chain was hitting the kick guard. FYI. With clutch pulled in, wheel pulls final shaft, tightening the bottom chain section. Conversely, with clutch engaged, engine pulls wheel, which tightens the top chain section (and loosens the bottom section).

If you really had a rattle in the clutch and tightening the chain made the noise go away - you have a transmission shaft bearing problem.

Skonnie Boy · « **Reply #21 on:** August 29, 2009, 01:10:25 AM »

You are correct. The sound I heard was the chain hitting the swingarm, as mentioned.

And thus concludes act 3 of Misdiagnosis Theater. I'm your host, Dontdothat.

JohnG · « **Reply #22 on:** August 29, 2009, 03:53:07 AM »

Since you guys have this thread going, maybe you can give me some advice in this area.

First I have a 1976 CB750F I bought new in 1976 (VIN 2011515 I believe).

Great bike; the clutch basket rattled like a bucket of bolts from the day I got it. The dealer synched the carbs. Honda came out with the GL1000 plate suggestion.

Nothing helped. The only flaw in an otherwise good bike.

33 years and 80,000 miles later the carbs just got synched, the motor rebuilt, new clutch, runs great.

So here are some options:
* get someone to balance the basket. I do not have a lathe or I would try it. Be happy to pay $$!

* since Honda did an upgrade, I assume that later 750s contain upgraded parts . I have a complete clutch (inner basket, outer basket, external cover, the whole 9 yards) from a black motored 750F (so gotta be 77 or 78) Thinking of transplanting all of that except the new plates.

At somepoint they are gonna cure cancer and put a man on Mars, so its seems like eventually I ought to get a decent idle out of this!!! Its not as if I haven't been patient...

Any sugestions??

John MA

tlbranth · « **Reply #23 on:** August 29, 2009, 12:12:44 PM »

When my 1970 was new it was smooth as silk. It idled quitly at 750 or so rpm with no rattles or pops. Not sure when things went south, but it sounds like a bucket of bolts at idle & it's rough. Runs great at speed but idle is nasty. Once it's warm, it'll idle rough at 1200rpm and that's about as well as I've been able to do. So I would love to hear a solution. It must be possible because it once idled so well. Sorry - no solution. But lots of sympathy - plus I'd like to be on the wakeup list for the thread in case the dithilium crystal solution comes in.

JohnG · « **Reply #24 on:** August 29, 2009, 02:35:29 PM »

I got out the parts from the 77-8 F. What I found of note is as follows:

* it has the thick metal plate for the center, which is GL 1000 in origin and shows up in the service bulletin that you guys provided a link to above

* it has a friction (fibre) disk on the very outside that is unique in that the tabs are wider than the tabs on all the other friction disks

* to accomodate this last disk, the slots on the basket are wider at the top (you see a step as you look at it)

So my initial guess is that they felt the outermost disk was making noise and went about trying to eliminate any play in it.

If someone has a parts list for the 77-8 F's we could see how the part numbers differ from the 75-6 Fs and also the Ks.

(I can take a photo if my description is too hard to follow)

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Author Topic: Clutch rattle - with a twist (Read 5780 times)