Chain or sprocket problem ?

[The Gecko_imp]

Observations as follows:
- chain is 6000 miles from new, no problems, no wear or visible damage
- sprockets same miles, looking perfectly fine
- sprocket mounting looks perfectly aligned, all nuts tight
- chain slack adjusted as required, hasn't changed in over 1500 miles

Now please help me explaining this.
When I measure the chain slack at different positions by rolling the bike forward (she has no center stand) the chain slack is the same in all but 2 or 3 positions. In those positions (each plus or minus 2 inches) the chain slack is reduced to under half an inch. No other observations. Adding plenty of oil and let it sit hasn't solved the problem.

I cannot figure any scenario {other than visible damage to the rear sprocket) which could cause such strange measurements. And I have a hard time ditching a good chain without a plausible explanation.

Has anybody seen similar ?

[Aussieflyer]

Hello Gecko,
Excuse me if telling you stuff you already know ...
I think you have checked the chain and sprockets for any deformation or build-up of grit on individual links or teeth. Variation in chain slack is often as a result of the sprockets and their attachment points being ever so slightly out of perfect round, imagine an oval shaped sprocket. This is just something that we live with but do ensure that you set the min slack at the tightest point on the chain.

[The Gecko_imp]

Both your answers make perfect sense to me. Thanks!
You know, there is things you sort of know, but when you face the problem unexpectedly, your brain doesn't make the connection. Will measure carefully again, adjust on a track stand, all the rest ...

Now let me ask one more question: if if came to replacing the chain, (and the rear sprocket asit ain't a lot of work to replace anyway), would you replace the front sprocket as well. I have the feeling I wouldn't be leaning that way for the effort involved ... and just see. And you ? what would you do.

[The Gecko_imp]

While you typed your response (thanks - I agree !), I went to the neighbor and borrowed his track stand for the rear wheel.
And guess what, as soon as she is lifted up the problem is entirely gone. The problem only shows when the bike is rolled forward as described before.
And as the track stand lifts the wheel near the axle (unlike a center stand) the rear shock does not decompress when the stand is added. In other words ... the geometry (sag) doesn't changes.
How the heck can this be ?

[The Gecko_imp]

Won't sweat it, I promise.
It's just that I like to know my bike and all it's features and conditions. Bothers me when something so (seemingly) simple has an attitude.

[Gone in 60]

I've had a similar situation with my Bonneville. Checking the chain slack with the bike on the sidestand, as it's supposed to be checked, I found it consistently loose except for one area, where it was much tighter. But on the center stand, it was consistant throughout its length. I didn't worry about it too much, knowing that the chain was nearing the end of its lifespan anyway.

[the Ferret]

I got 37,000 miles out of my original chain and sprockets and have 38,000 miles right now on its replacement set

[The Gecko_imp]

@Gone and ferret: see - not living up to my promise - here is what bothers me after all.
If there was a little difference of say under 1/2" between measurements, whatever, I'd just leave it alone. But when I adjust the chain to about 35mm slack as by the book, and go back on the side stand I find the same 35mm. Then I role her forward to the tricky spot and I measure ~5mm. It feels super tight. And that means the gear box / forward sprocket will sense the same.
If I ruin the chain, to hell, I replace it. But if the tight chain - which I cannot loosen any further" - pulls hard on the gear drive for every revolution of the chain, that can't be good.
And I still don't know how come.

[the Ferret]

You always adjust a chain to spec at the tightest measured spot along the lower chain run.

So if it were me, I'd go to that 5 mm spot and adjust the chain to read 35 mm slack, and then measure it at the loose spots. I would not ride it how you have it adjusted.

I can't imagine a chain having a spot THAT much different than the rest of the chain in 6000 miles, but if it truly has that tight of a spot, I suspect the chain is toast.

I personally at 6000 miles would just replace the chain and continue to run the original sprockets unless they show extreme wear as in hooked teeth with pointed tops.

[Gone in 60]

I agree with Ferret on this one.