TOPIC:

On my 750, I've got a strange vibration that seems to occur INTERMITTENTLY around 3000-3750 RPM, and only with a *particular* acceleration level. I mean I can back off the throttle a wee bit, or get on it a bit more, and vibration (mostly) stops. Lately it's happening more and more...

My hunch WAS an out-of-alignment chain/sprockets, but I checked and re-adjusted them and they are good.

Anyway, I've looked through the forum, and found some great advice on FIXING the failing cush drive, but not really anyone describing the SYMPTOMS of a failing cush drive.

One of the items describes that if you can move the rear sprocket at all while the bike is on it's sidestand, the cush is shot. Mine *does* appear to move slightly, so I'm assuming this is the problem... and hoping it's not a failing transmission! I'll be attending to the cush soon, and of course I'll report back...

So, can anyone corroborate the vibration symptom, or should I be looking at something else as well?

Thanks!

How much does it move?
When I got my bike, my sprocket could move 1/8" in each direction, (1/4" total). It was snatchy and hard to accelerate smoothly. I tore the hub apart and used Auto Goop to build up the cush rubber sides. A cheap and easy fix, the Auto Goop has higher shear strength then the black windshield rubber that is recommended for this fix.
My hub/sprocket has no slop and 4000 miles now, works great IMHO.

Biquetoast wrote:

One of the items describes that if you can move the rear sprocket at all while the bike is on it's sidestand, the cush is shot. Mine *does* appear to move slightly, so I'm assuming this is the problem...

So, can anyone corroborate the vibration symptom, or should I be looking at something else as well?

Thanks!

By the very physics of the cush/sprocket interface, there is *always* going to be a small amount of play in the sprocket - that's what it's there for. 1/8" either way isn't excessive.

Crashed cushes are generally a symptom of *major* hole-shot action...

Before I'd suspect the cush, I'd make sure the wheel is in balance and the chain isn't stretched in one particular spot - both of those can and will cause symptoms like you're seeing...

Another thing to check is the axle nut - if it's a wee bit loose, it'll do funny things as well...

But, that said, inspecting the cush is an easy deal..

If one whole side of the rubber cush drive was missing, then it might cause some vibration, a cush drive normally goes bad everywhere not just on one part.

Keep in mind the cush drive is located right close to the center line of the axle, and the closer an out of balance condition is to the center the more weight it takes to be noticable.

4 ounces on the tire is about like 40 ounces at the cush drive (roughly).

Highly unlikely that the cush drive would cause the vibration, chain/sprockets are much more likely to be the culprit.

Other possibilities:
Loose engine mounting bolts.
Carb related problems.
Balance shaft related (unlikely but possible).

steell wrote:

...Highly unlikely that the cush drive would cause the vibration, chain/sprockets are much more likely to be the culprit....

Well, as it turns out, it was definately the chain, but I don't think it all ends here...

Ok, so I managed to find some open road, going about 50mph, at the right RPM, and I kept looking down at the chain (dangerous!). It took a while, but I finally saw it happen - the bottom part of the chain was flapping side-to-side pretty bad, and that's what caused the vibration.

So, I went home, tightened up the chain as tight as I felt safe -- not stiff, just correctly tight (it wasn't really that bad to begin with). That brought the vibration down to almost nothing.

Here's what's weird though. I got to some open road again, looked down, and it was still doing it a little bit! Still intermittent, and still side-to-side flapping. But now that the chain is tighter, I really don't feel it. To repeat - it's only once in a while, only at a certain RPM range, and only when accelerating -- letting off the throttle stops it.

Is this normal??? I don't like it...

Is the engine sprocket retaining nut torqued up and held in place with a washer?
OOOPS, I re-read your post, looks like you are on that.

Post edited by: gas, at: 2006/06/10 21:11

How old is the chain? I have seen old chains that were so stiff you could almost hold them straight out in front of you. Might consider taking the chain off and checking it out.

gas wrote:

Is the engine sprocket retaining nut torqued up and held in place with a washer?
OOOPS, I re-read your post, looks like you are on that.

Thanks anyway, though. I apreciate any tips. You never know I might have forgotten the obvious.

steell wrote:

How old is the chain?

It's a new enough chain too; an RK x-ring, about 2/3 years old, maybe 5000 miles or so (same with sprockets). Maybe I don't lube it enough... I did today though, and I usually do it about once a month...

Post edited by: Biquetoast, at: 2006/06/10 22:05

Metal to metal noise on take off,park the bike and move the sprocket if you have any movement its time to check the rubber damper (cushion drive).I allready replaced one on my ZX 1100.