GS550 Bottom End Rattle/Knock

[DaleGribble]

Hello all,

I picked up a 1977 GS550 last year and got to ride it for the back half of last season after fixing a weak/no spark condition in cylinders 1 & 4.


A few weeks ago, I went to start the bike up one last time before tearing into it to do some work over the winter like checking valve clearances, swapping valve shims, replacing old gaskets, and some other odds and ends. I started it up and heard a knocking/rattling sound coming from the bottom end behind the LH crankcase cover.


I've heard a much quieter version of this noise a few times before, but it'd always go away after a few minutes or if you started riding. I'm not sure if it's getting worse or was just the fact that it was 25°F that day, but the rattle was significantly louder. The noise only occurs at or below idle and goes away when giving it some throttle.


Does this noise sound familiar to anyone? I'm hoping to get some ideas before I start tearing into it. Could this be loose starter clutch bolts? connecting rod bearing? (fml) I wouldn't think out of sync carbs would cause such a noise, but I'm not certain. PO said he went through the carbs and synced, but you know how that goes.

https://imgur.com/a/1977-suzuki-gs550-bottom-end-rattle-lvziMsB

[rphillips]

GS's are known for clutch rattle, but yours seems different than most I've heard... No clue.

[dgates1]

Sounds like something to do with the starter clutch. Can't be sure, but I would take that cover off to see what's going on.

[oldGSfan]

I got my volume up and can hear YouTube etc, but nothing on those posts. Is there some volume icon I'm missing? I got nuffin.

[dgates1]

I got my volume up and can hear YouTube etc, but nothing on those posts. Is there some volume icon I'm missing? I got nuffin.

There is a "speaker with an X" in the bottom right corner to be able to hear the sound.

[oldGSfan]

There is a "speaker with an X" in the bottom right corner to be able to hear the sound.

Not on mine there ain't. Anyway, as long as some can hear.

[Rich82GS750TZ]

I don't think you will know until you take the stator cover off. Something in there isn't happy. Rotor magnet come loose? Starter clutch gear bolt sheared? As long as you're replacing gaskets anyway, get one of these too.

[rphillips]

Mine's like his blue line at bottom with speaker at right end, if X is showing no sound, click on it and X goes away and sound comes on.

[Michael Graziosi]

It certainly doesn't sound like the typical GS clutch noise when the clutch lever is released in neutral. It's certainly rapid and (probably not isolated to one cylinder/valves) sounding like something is loose (bolt/nut perhaps), rotating and hitting something . My description of the noise is that it's more like a clicking sound. When the rpm is increased, the noise does seem to go away. However, it might be just that at higher rpm, the clicking sound is occurring rapidly blurring the clicking into a continuous sound. I know that the 2 valve GS750 engine had some problems with the starter clutch going bad but I'm not sure about the GS550 engine.

[dgates1]

Rotor magnet come loose?

Could be a loose rotor magnet. Hits the stator at lower RPM then centrifugal force pulls it back out at higher RPM.

[Big T]

There is so little clearance between the starter clutch and the starter gear that a loose clutch bolt will contact the gear.

The last time I had to replace my starter clutch bolts, it turned out that the bolts I bought at Ace Hardware had heads that are .5 mm longer than the previous supplier. This, they dragged on the starter gear.

Fresh bolts, a bit of time on the lathe trimming the heads and it's been good ever since

Pull the cover and have a look. It's all speculation until you do that

[Rob S.]

Am I correct that it seems to stop at higher rpms?

Sounds worse than a 'click' to me. On the plus side, if it only happens at idle,...

But, before dismantling engine (or just opening it), double (triple) check that it's not an engine or exhaust mount, side or center stand, filter cover, etc. Stranger things have happened.

[DaleGribble]

I appreciate all the insight. I'm planning to open the stator cover and start digging into it tomorrow. I'll come back with updates. Makes me nervous some of y'all are saying it doesn't sound like the typical loose starter clutch bolts. Fingers crossed it's nothing too crazy.
I've for sure narrowed the noise down to behind the stator cover using a stethoscope. The noise does seem to cut out completely at higher rpms, anything above idle.

I didn't consider it could be a loose rotor magnet. Is that a common repair on these bikes? I'd think even at idle there'd be enough centripetal force applied, but I could be totally wrong.