Knocking sound at idle?

[GS750cafe]

Got the bike up and running again today (thanks for tips on the oil change). She ran pretty good despite needing rejetting (4-1 and pods). When at idle though, there was a rhythmic knock sound coming from the engine. It would stop when revved or being ridden. Any ideas? Thanks for all you help everybody!

 

[tkent02]

Clutch rattle? Carbs out of synch? Exhaust leak?

 

[1948man]

Maybe search "cam walk" or "cam end float". Also possibly clutch noise. I'm not the expert to really describe it all.

 

[GS750cafe]

Sucks to be so illiterate with motors, but I'm learning! The sound is definitely not the carbs or exhaust. I don't think it's the clutch either. Sounds like it's coming from the depths of the engine... maybe something to do with the cam. Seems like it's more pronounced once it's warmed up good and then idleing. I drove VWs buses for a while, and there was always talk of knocking sounds being associated with throwing a rod. But, there aren't rods in this motor are there? Cheers

 

[tkent02]

It's got connecting rods, but they don't go bad much. Unless you have a 1980 - 1982 750.

 

[GS750cafe]

This is a '77 GS750 with just over 12k original miles on it.

 

[tkent02]

No, that motor is just about indestructable with ten times that many miles.
It's not going to be a bad rod. Have the carbs been synched?

 

[GS750cafe]

Not sure. I just bought it a few weeks ago. The throttle response seems good. Its just when I ride, then stop there is the knock or tick about aver second or so at idle.

 

[tkent02]

Like tick, tick............................tick, tick................................tick, tick?
Quite a long interval between each pairs of ticks?

 

[Steve]

Yep, sounds like "cam walk".

Rather than "revving" the engine, increase speed slowly. If the noise goes away between 12-1500, it's almost guaranteed to be cam walk.

More annoying than destructive, many of us just live with it, although a few have found cures.

.

 

[GS750cafe]

I don't recall much time between pairs of ticks. More like tick...tick...tick...tick
But I might have to start it again to get a better sense. It's almost like you can feel the tick...

 

[Steve]

Can you get a video (or audio) recording and post it?

.

 

[GS750cafe]

I'll see if I can't get some (video/audio) tomorrow. Although I think it's snowing outside and I don't have a garage! We live in a barn (literally) and I'm working on the bike in a horse stall! Talk about horse power!

 

[GS750cafe]

[youtube]watch?v=N9bha5LVJAs[/youtube] <--- that didn't work.

Until I figure out how to embed video, her is the youtube link: http://www.youtube.com/watch?v=N9bha5LVJAs


Aside from the exhaust leak, you can here the ticking sound at idle. Now that I hear it again, tkent02, you might be right.
Let me know what you think.
Cheers

 

[chuck hahn]

My money is on the clutch basket springs being worn out. I got a 77 and a 78 with both of them being over 35,000 miles and not as much as a fart out of the top ends..the early 80s..now those are different animals all together!! I say pull the basket and i bet the springs are loose. Theres a lot of in fo on here about rebuilding the baskets and i even think there are afew places you can send them out for repair as well.

 

[GS750cafe]

Thanks Chuck. I'll give the clutch springs a look. There's no harm in pulling the basket even if the springs are ok, right?

 

[tkent02]

Thanks Chuck. I'll give the clutch springs a look. There's no harm in pulling the basket even if the springs are ok, right?

If it's clutch related, the sound will go away or at least change when you pull in the clutch lever. Does it?

I hear two sounds, a dull thump every rotation that you can hear in the first seconds of the video, and a tick tick every few rotations that can be heard when the camera moves farther back, and from the right side. The dull thump could be due to poor carb synch, cams walking, even and exhaust or intake leak, not sure what else. Doesn't sound too serious, it's a GS. Have you vacuum synched the carbs? Are there any exhaust or intake leaks? The tick tick I believe has something to do with the cam chain, as it timing of the ticks is once every several rotations, about how often the chain goes around the sprockets. My 650 does this, a friend's 750 does this, I have heard it on a few others. Also doesn't sound too serious, none of these bikes have had any failures yet. We have pulled the valve cover on the 750 and checked for a bad link going around, couldn't find anything. Ride it and smile.

Just listened again, by the way the acceleration lagged when you blipped the throttle at the end, the carbs are out of synch, quite a bit.

 

[waterman]

Like tick, tick............................tick, tick................................tick, tick?
Quite a long interval between each pairs of ticks?

If it's clutch related, the sound will go away or at least change when you pull in the clutch lever. Does it?

The tick tick I believe has something to do with the cam chain, as it timing of the ticks is once every several rotations, about how often the chain goes around the sprockets. My 650 does this, a friend's 750 does this, I have heard it on a few others. Also doesn't sound too serious, none of these bikes have had any failures yet. We have pulled the valve cover on the 750 and checked for a bad link going around, couldn't find anything. Ride it and smile.

Best description yet of my tick problem in my 650. I drive a 2 miles down my road, stop at a signal and bike will tick tick.....tick tick.... at idle. Drive another mile and usually gone. Not everytime but often. Have to agree, it sounds like cam chain related. Also will concur with Ride it and Smile.

 

[chuck hahn]

The spring rattle in the clutch SOMETIMES will go away if you pull in the clutch but not always. Mine didnt on my 78 750E and i was thinking my engine was toast so Rustybronco decided to come over and have a look and he discovered that the springs were loose where as i didnt think they were all that bad. So moral of the story is check evrything visually and thoroughly yourself. Even if you pull in the clutch lever the basket is still spinning so it will still clatter. And also remember that bad valve adjustment coupled with bad carb syncing will make the engine rattle quite loudly also. There may be a combination of things causing these symptoms.

 

[raistian77]

Yep, sounds like "cam walk".

Rather than "revving" the engine, increase speed slowly. If the noise goes away between 12-1500, it's almost guaranteed to be cam walk.

More annoying than destructive, many of us just live with it, although a few have found cures.

.

nah, sounds like the little gremlins that make engine go are bored and rapping on the casing. I found if you rev it up it makes the little buggers work and they have no idle (har) time to smack random stuff with their hammers.