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GS550 Bottom End Rattle/Knock

D

DaleGribble

Forum Newbie
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
 
GS's are known for clutch rattle, but yours seems different than most I've heard... No clue.
 
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.
 
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.
 
oldGSfan said:
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.
Click to expand...

There is a "speaker with an X" in the bottom right corner to be able to hear the sound.
 
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.
 
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.
 
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.
 
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
 
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.
 
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.
 
I finally got around to tracking down the source of this ticking/knocking sound.

After many hours spent whacking away at the stator cover with a rubber mallet, it eventually popped off.

It ended up being a dislodged rotor magnet. Photos and videos are linked below. I'm surprised the stator isn't destroyed from coming coming in contact with that magnet.

Sourcing a replacement rotor has been a bit of a mixed bag (partially due to some folks calling it a flywheel or lumping it in with the starter clutch assembly)

My bike is equipped with the ND generator/starter assembly. I see a lot of Kokusan rotors and starter clutch assemblies for sale on eBay. The ND versions seem a lot harder to find. I ended up ordering a ND rotor (part #31402-45011) that came off a 1977 GS750 because the part # was the same. Here's the replacement I bought.

Are the Kokusan and ND rotors interchangeable?

https://imgur.com/a/7dGefpk
 
The early bikes like this used a 12 pole charging system. Later bikes, 18. You need the matching rotor. The 750 shares the rotor with the 550, so it looks like you found the correct part.
 
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