Topic: CB 500 neutral coasting noise?

[hndlbrs]

Okay, anyone come across this?

I have a 73 CB 500 and I just took her out for a weekend rip. The bike ran amazing the whole time, and as I was wheeling it into the shop (engine off) I noticed a rhythmic knocking coming from inside the engine bottom or potentially sprocket cover.

So I put it up on the centre stand and rotated the back wheel in neutral. There are 3 distinct knocks. The first one is quiet, the second louder, and the third is loudest. The rhythm seems timed to match the rotation of the front sprocket, not the chain itself. This only happens with the rear wheel rotating forward, and is not there when I rotate in reverse.

With the bike still on the stand I started it up and put it in 1st gear and let the idle drive the rear wheel. Sounded fine. I revved it up a bit and still sounded great. Any ideas?

Thanks,
Jacob

[Greggo]

Only four screws to get the sprocket cover off.  I'd check there first, and check on your sprocket, chain, and lube the clutch lifter mechanism too.

[hndlbrs]

Yeah
I know
Only 4 bolts to check may make me seem lazy, but what I forgot to mention earlier implies it's something I won't likely be able to see just by taking the cover off.

It seems when I find a spot with a clunk, then move the wheel a few inches back to find it again, it does not repeat when I move it fwd again, as though whatever has moved only moves in one direction, and has to continue on until the next rotation. Does that make sense?

So to me it points to whatever is clunking can't be the chain against the sprocket itself, since if it were a worn tooth or stuck link then it would clunk again when I backed off then moved fwd again. To me that suggests something further inside that does not move when the engine is static. I hope that makes sense. It's acting like how a bicycle sprocket allows you to pedal forward but coast without the pedals going around.

Could it be related to the kick start somehow, since it is a ratcheting mechanism?

BTW this forum rules!

[dave500]

put it on the centre stand and drop the pan and have a look,these often make a little clunk/ click like you describe,the forks and drum slots wear and the gear dogs might be just snicking on a couple,try pushing the bike with it laid well over to the left,,then try it laid over to the right,,the gears might quieten up leaned one way or the other,dont worry about it if its not real savage,drop the pan though and have a look.

[hndlbrs]

Ok thanks I will try the lean and push method first since I don't have a spare pan gasket kicking around. If either direction of leaning made it less apparent or go away entirely, then what would that indicate?
I'm trying to find out if this is a safety issue. Or if riding it will cause more damage.
Like I said it seems to drive just fine, but wouldn't want to risk a lock-up. Any idea what I should be visibly checking for once the pan is off?
J

[dave500]

the pan has a large rubber seal you can reuse a few times,if the shift forks are worn gravity can let a gear slide either way so its dogs are ever so slightly contacing its mating gear,if its not jumping out of gear and selects when you shift easily itll be ok.

[hndlbrs]

Ok so if I understand this correctly, the gears will slip ever so slightly side to side and cause the teeth of one to contact another at a point where it comes around?

And this is not an issue if it's in gear?

Reason I really want to know this is I have promised my girlfriend I'd ride out and pick her up from visiting her folks which is about 500 miles away. As much as not letting her down would have some value, I'm not sure it's worth a wrecked bottom end

Or is it....

Ok I think I will carefully ride it to my shop tomorrow and have a look under the pan
Thanks
J

[hndlbrs]

As an afterthought, at one point on the ride I accidentally downshifted from 4th into third without pulling the clutch, could I have bent a gear sprocket a little or chewed the corner off a few cogs?

[dave500]

if you were preparing to down shift anyway and it went in ok it should be ok,all the teeth on all the gears are always in mesh,constant mesh,the gear wheels slide from side to side engaging a male dog into a female slot for want of a better wording,you might find tiny metal shards in the pan bottom and this is normal on an older gearbox,if you have an entire dog piece or bits of gear tooth its not so good.

[hndlbrs]

Ok
That's very helpful, I'm beginning to see how these things work inside.
No I was not preparing to downshift. It was one of those oops moments. Hmmm...

Thanks, I will reply after I've had a sleep and some breaky and then a good look inside.
Thanks Dave
J

[hndlbrs]

Ok so here's what I found.

I dropped the pan. There were some small bits of metal inside. About the size of grains of salt or a little bigger. Not much of it either. I could not see anything rubbing or binding with any of the gears. When I leaned and rolled it around it did seem to take care of one, maybe two of the knocks, but the loudest one is still there. It still rides and shifts just fine, with no hint of noise.
With the sprocket cover off, there is nothing to show that anything is wrong with the sprocket or chain.

Should I just ride it and see if it gets much worse?
Again, is this a hazard or could anything lock up while riding?
Should I switch to a 550 bottom? Kinda don't want to do this, as I just put in a new Barnett Kevlar clutch and it grips real nice.

If anyone out there thinks riding it is a bad idea, please chime in here.

Thanks
J

[dave500]

the first trouble will be itll jump out of gear on hard accelleration or get a bit tricky to shift,id just ride it,some noise is "normal" on and older bike,you did rotate the wheel with the pan off and looking up into it?

[hndlbrs]

Okay,

So I took the sprocket off and rotated the shaft by hand. There were no noises or noticeable hard spots in it's rotation. I thoroughly cleaned the sprocket and the keeper and replaced the parts and bingo! No more noises! Not sure exactly how it fixed the problem, but it seems to be just fine now. Maybe by putting the sprocket back in a different position on the spline or maybe having cleaned some hardened old gunk off the back of the keeper made the sprocket sit straighter on the shaft somehow. Anyway, she's back to her old self again. Had me worried there for a bit.

While cleaning the pan I noticed a crack right where the drain plug goes. Lucky there was a spare pan kicking around (thanks Chris!)

Now I can get back to deciding between staying with clip ons or switching to tracker bars...

[Coyote13]

I didn't read through this whole thread since I'm at the office, but how does your chain look?  My 750 was doing the exact same thing you're describing, it was due to a loose/old final drive chain.