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Just bought 1978 GS750 -Rattle grinding noise

  • Thread starter Thread starter kfb
  • Start date Start date
K

kfb

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I took the cycle out for the first extended run and heard some disconcerting noise.

Engine Runs pretty smooth and starts quickly.

Shifts well up and down between gears.

However when going down hill (coasting without throttle) I hear intermittent grinding/rattling noise. The noise appear to coming from the front of the bike...engine/transmission... loose part...I check for loose parts but didn't see any... I hear it best on the left side of the bike.

Any ideas? is this a GS750 issue?

The bike has 18K. I believe this to be accurate because the title confirms it and the PO had the bike for about 4 years.
 
Starter clutch/primary or secondary starter gear....Behind the rotor under the stator cover...common for them to go bad. They start spitting springs and bits out..so id tend to it soon...
 
Thanks for the info... so you are saying the gear that the starter engages... sort of like the fly wheel (car terminology) is loose or bad?

Any idea on parts cost and degree of difficulty to repair? I have done a fair amount of mechanic work but am not a professional.
 
Wheel?

Wheel?

I don't think that it is coming from the wheel as it only makes the noise when I let off the throttle. It is before I apply the brake. I will have to take it out for another spin to get more info.

Thanks!
 
Another possibility

Another possibility

It could be chain slap or the chain jumping the front sprocket. The back sprocket is good... I can't get the front sprocket cover off because of a stuck screw. It may be as simple as a bad counter sprocket? Except that wouldn't the counter sprocket be as likely to slip going up hill as down? It doesn't make the noise on the way up hill:-k
 
kfb said:
It could be chain slap or the chain jumping the front sprocket. The back sprocket is good... I can't get the front sprocket cover off because of a stuck screw. It may be as simple as a bad counter sprocket? Except that wouldn't the counter sprocket be as likely to slip going up hill as down? It doesn't make the noise on the way up hill:-k
Click to expand...


Stuffed link in the chain? lube ya chain up like all hell and see what difference you get, how much slack do you have in the chain, you want about an inch in the middle with no load on the chain...

to get the screw out put a bit in it and tap it with a hammer 20-30 reasonable hits and you should have no problem getting it out...

or use the right tool for it i cant remember whats its called... you hit it with a hammer and it shock spins it... i find you are best to hit the bit into the screw head with a hammer first to get it fully in, then put the tool on the end, sorry i cant for the life of me remember the name of it.
 
kfb said:
It could be chain slap or the chain jumping the front sprocket. The back sprocket is good... I can't get the front sprocket cover off because of a stuck screw. It may be as simple as a bad counter sprocket? Except that wouldn't the counter sprocket be as likely to slip going up hill as down? It doesn't make the noise on the way up hill:-k
Click to expand...
\
i would agree and say it is most likely a mal-oiled chain or just a smiple chain slap. caused by a worn chain and/or sprockets. easy fix.
 
kfb said:
Thanks for the info... so you are saying the gear that the starter engages... sort of like the fly wheel (car terminology) is loose or bad?

Any idea on parts cost and degree of difficulty to repair? I have done a fair amount of mechanic work but am not a professional.
Click to expand...
Well, BEFORE you go tearing into, appease yourself and everyone, by checking your countersprocket. I personally dont think that your noise is related to that, but Im not an expert either. I have a couple of 750s, and more than a couple of 750 motors, and yes, the starter clutches are a common annoyance. Dunno why, but they're prone, even more so on the big bikes, to start trying to eject their innards and such. But, USUALLY, this problem is accompanied by a loud CLACK noise when starting the bike from cold. Not always tho. My 1100ES i think has a starter clutch starting to go, and it starts up just find. There is an intermitant grinding noise coming from that cover...just my thoughts...
 
Thanks for the responses

Thanks for the responses

I looked at the manual and the starter clutch detail. Typically, what components inside are going bad and causing the grinding noise? There appears to be a Starter Gear and the rotor. Will it be obvious when I pull the cover as to what is wrong? Like pieces of metal shavings?
 
Last edited:
skidMarkNZ

I believe what you are referring to is called an Impact Driver, they are great tools, good point about tapping the bit in first, I always do that as I have seen a few people strip out the screw head because it wasn't fitting good when they struck the hammer.

Steve E.......
 
kfb said:
I looked at the manual and the starter clutch detail. Typically, what components inside are going bad and causing the grinding noise? There appears to be a Starter Gear and the rotor. Will it be obvious when I pull the cover as to what is wrong? Like pieces of metal shavings?
Click to expand...
Basicly, inside the starter clutch there are three main components. There are three springs, three "pushers" ( i dunno what theyre really called but thats what i call em) and three throw-out barrels. Basicly how they work is when you turn the starter over, the spring loaded pushers push the throw outs in toward the center of the clutch, which in turn grab the crank, turning it. Once the crank is spinning faster than the starter motor, they basicly let go. Over time, for whatever reason, these things actually try to push their way out the BACK of the clutch. you'll see some dimples sticking out of the metal on the sides of the clutch..when the space becomes wide enough, the springs and what not will simply fall out of where they are jammed, and find their way thru your oiling system lowers...Ask me how i know. At any rate, you will need a special tool to pull the charging rotor to replace the clutch. These can be had from Z1Enterprises or various parts supply shops...Simply called a rotor puller. There were TWO different kinds used, but you will need the external threaded one i do believe. They arent expensive, but the clutch pack can be. I would suggest getting a NEW one, rather than simply trying to repair the one you have, cause generally that fix wont last very long..
 
Good Explanation

Good Explanation

Thanks Cafe Kid. As I read your description of the operation I can see on the parts drawing... the spring, push piece and roller... It all makes sense.

But here is the MILLION DOLLAR question: what causes the roller (barrel) to engage the starter clutch gear when I let off the throttle or after downshifting on a hill and not during regular acceleration?
 
Its not engaging as far as I know. the rattling that you are hearing is simply the peices rattling around in their now loose homes. Also, and im not saying this is for sure your problem, as the starter clutch wears, alot of the time they get loose from the primary, and allow it to skip teeth and rattle around it itself...again, I would investigate other suggestions as well, but im simply saying its a fairly common issue, and the symptoms you describe sound fairly familiar to me as being the stater clutch..
 
kfb said:
But here is the MILLION DOLLAR question: what causes the roller (barrel) to engage the starter clutch gear when I let off the throttle or after downshifting on a hill and not during regular acceleration?
Click to expand...

Take it apart and look at it until you grok it.
 
Chain slap!

Chain slap!

I put the bike on the center stand and checked the counter sprocket and chain slack. The sprocket is not worn and the chain slack appears to be okay. However when I start it up and put it in 1 gear up to about 3k and let off the chain is bouncing up and down a lot. I hold the throttle at 3k and kneel down by the back wheel and I can hear and see the chain slap the bottom of the frame as I let off the throttle. I guess I need to tighten up the chain a little and see if that solves it.
 
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