Rattle at 6k ('82 GS450)

[JustRon]

I'm pretty mellow, and don't often go over 5k on the tach, but I've noticed when I get to 6k, there's a rattle. I think it stops when I get beyond 6k, but I can't recall.
I'm not even sure what to check. I know that my tach can sometimes act strange (the PO said it needed a new cable, but it usually works fine).
Any ideas on where to start?

[Steve]

I was thinking "how can he possibly NOT go over 6k on a 450?", then I saw that you are stuck in "town". Sorry about your luck.

There are many kinds of rattles, each has a different sound. See if you can find somplace where you can run it up to 6k with the bike on the centerstand, then move around to see if you can locate the rattle.

One possibility is a chrome cover on the exhaust. It is not uncommon to lose a screw or a clamp, then the rest of that cover will rattle.

.

[JustRon]

One possibility is a chrome cover on the exhaust. It is not uncommon to lose a screw or a clamp, then the rest of that cover will rattle.
.

Wouldn't that rattle all the time? It's weird that there is no rattle at all below 6k.
I should try it in neutral, although I don't have the balls to do it in gear on the centerstand. I can just picture me slipping or falling and landing on the back of the seat, so the rear tire catches the ground and launches the bike into [who knows what].

[Steve]

Wouldn't that rattle all the time? It's weird that there is no rattle at all below 6k.

Think "Resonant Frequency".

I should try it in neutral, although I don't have the balls to do it in gear on the centerstand. I can just picture me slipping or falling and landing on the back of the seat, so the rear tire catches the ground and launches the bike into [who knows what].

Nobody said it had to be in gear.


"Engine at 6k" is "engine at 6k" for these purposes. You just need to get the engine vibrating at or near the frequency that will set up that resonance.

The suggestion to "find someplace" was more for noise issues than anything else. 6k gets a bit noisy, even with stock pipes.

.

[JustRon]

Nobody said it had to be in gear.

Ahh, got it. When you said "centerstand", I thought you meant for it to be in gear.
Thanks for the explanation.

[Steve]

Nope, that was just so you did not have to balance it whilst holding the throttle and walking around it.

.

[JustRon]

So, it was resonant fq... and, really easy to spot. A bolt that holds the [aftermarket?] engine bars to the frame was super-loose, it wasn't threaded at all. It couldn't fall out, because the exhaust was in the way.
Thanks for the help!

[Steve]

Thanks for the report.

Glad that it was an easy fix.

.