Topic: Gearbox/clutch whine

[garrettmiklautz]

Hey guys,
Ive recently noticed a slight whining noise coming from my 77' cb750 under acceleration.
I have read similar threads on this but it hasnt helped me narrow down my issue.

Its loudest starting out in first, not bad in second, and loudest in third.
I believe its coming from the drive side, which makes me question if its the clutch. My drive chain slack is set properly, maybe even on the loose side. I have also messed around multiple times with my clutch adjustment to see if anythinf changes. No luck. The noise gets louder with more acceleration, and dissapears as soon as the clutch is engaged.

Im aware of the sloppy cut gears that will create a noise, which i suppose this could be. But id like to know if this is a normal symtom on these old bikes, or is somethings worn or not adjusted correctly.

Thanks!

[jaytee-nz]

I have a similar issue with my CB750 but the two noisiest gears are third and fourth.
I asked the question on this forum but didn't get any definitive answers. I don't think it can be clutch related as the clutch operates the same regardless of what gear you are.
My suspicion is simply slightly worn gears within the gearbox (by the way, my bike has travelled about 33,000 miles). 

[garrettmiklautz]

Thats a good point with the clutch. I guess if it was clutch related it would be consistent through all the gears. Id say third gear on mine is the worst, than 1st than 4th. My old DR650 had a notorious third gear whine, which was common amongst thise bikes. But wasnt quite as noticable as this.

 23,000 miles on the clock.

[jonda500]

My 500 has this - louder if I accelerate harder and disappears when I pull the clutch in. I don't think it is normal as my other bikes don't do it. My best guess is that a transmission bearing may be on the way out?
John

[garrettmiklautz]

Not to jump to conclusions, but are these tranny related bearing only accessible by doing a full engine tear down. I've read a few threads related to worn bearings creating a similar noise.
Im fairly mechanically inclined, but the thought of splitting the cases at some point down the road seems quite daunting.

[BomberMann650]

My 550 is a real whiner lately too.

Would love to hear anyones experience with this topic.

[jonda500]

I would think yes, the cases need to be split to change the tranny bearings. I am finding the prospect a little daunting - and now I'm facing all three of my bikes needing the cases split - something I haven't done in over twenty years!
John

[garrettmiklautz]

Sounds like i am not the only one with this issue.
I guess im just hoping im not causing further damage or wear to other parts as a result of whatever this symptom is.

[flybox1]

Why not open up the clutch and check the plates(cable adjustment) before resolving to pull the engine?
Pulling the engine is the toughest part.  Opening, cleaning, changing bearings is very straightforward.

[garrettmiklautz]

On the to do list. Ive messed around with my clutch cable adjustment numorous times, and im pretty sure its correct but im not sure.
I have a hard time judging how much resistance to put on the bolt before going back a quater turn. I suspect i maybe dont have enough because it disengages quite late, but isnt slipping to my knowledge.

[garrettmiklautz]

After a long ride yesterday, ive realized its my fourth gear thats the worst.
Maintaining a consistent speed and rpm around 80km in fourth, it has the whine and seems to be kinda jerky, or not able to ride smoothly in that range.
Still gotta open the clutch up, but could this be possibly fuel/ignition related as well?

[HondaMan]

Most of these that I have seen are due to the needle bearings inside the primary driven sprocket (which powers the mainshaft and clutch). It cannot be accessed from the outside, though, cases have to be split to get at it. You can try this to help diagnose it: add some zinc (you can get little bottles of it online, ZDDP additive - don't use Rislone or Lucas stuff) to the engine oil and see if it gets quieter over about 200 miles or so. If it does, the needle bearings are likely pitted.

Also, BE SURE the oil you are using is NOT car engine oil with their typical high-detergent, low-zinc formulations today. Instead, use at the least, Diesel-rated oils in 15w40 (do not use 10w40 in the SOHC4 engine in summertime, ever...) or something like real motorcycle oils. One excellent one today is the Bel-Ray Mineral EXL series oils, in 15w40 or 20w50 (my personal favorite for these).

Car oils with their high-detergent formulas cause oil foaming. This reduces lube to the needle and roller bearings in these engines a WHOLE lot, as they are all splash-oiled inside. When foaming, oil does not have any film strength, and roller bearings get noisy under those conditions.