strange noise when warm...?

[fnkvn]

My '79 GS850G just developed a strange noise. It turned 16k yesteerday, and when I stopped at a light, it sounded like an air leak or something. The bike runs as normal, and makes power all the way through the powerband, but there is a distinct noise that now could be described like a dry cam chain. When I first start up, it sounds normal, but within 2 or 3 minutes, the sound comes back. When the bike shuts down, it sounds like a dry bearing, squeaking to a stop.

I know it is hard to diagnose, but short of pulling the top end off for a look see, any ideas?

 

[Guest]

Wuh Wo Astro
I say check the cam chain tensioner first
I hope it not a crank bearing.
Can you determine if it's coming from the top end or bottom?

 

[fnkvn]

It sure sounds like the top end, but you know how noises bounce around.

 

[Guest]

Havn't experienced it myself, but my Clymer manual desrcibes a similiar sound can come from a compression leak - spark plug loose or head gasket?

 

[Big T]

It sure sounds like the top end, but you know how noises bounce around.

Track it down first, don't go tearing the engine apart until you know where it's coming from

Spark plugs = easy

Head gasket = spray with soapy water while running. look for bubbles

Cam chain tensioner = Basscliff's site

 

[BadBillyB]

My '79 GS850G just developed a strange noise. It turned 16k yesteerday, and when I stopped at a light, it sounded like an air leak or something. The bike runs as normal, and makes power all the way through the powerband, but there is a distinct noise that now could be described like a dry cam chain. When I first start up, it sounds normal, but within 2 or 3 minutes, the sound comes back. When the bike shuts down, it sounds like a dry bearing, squeaking to a stop.

I know it is hard to diagnose, but short of pulling the top end off for a look see, any ideas?

Spray some soapy water around the carb intake boots and see if it gets sucked in.....A vacuum leak on shut down can sound like a squeak......Billy

 

[tatu]

Does it have points ignition?

 

[fnkvn]

Does it have points ignition?

Yes, it does.

 

[tatu]

Then it might be worth checking to see if the pionts heel is lubed ok.
One drop of oil on the oil wick should do it.

 

[nert]

sounds like we are just throwing things out there. does the sound have a beat? compression or sparkplug would have an "on"-"off" beat. not steady like a vacuum cleaner. A vacuum leak might be steady. What happens to the noise when you blip the throttle? is it engine speed, half engine speed. Hold in the clutch, make difference, put it in gear, make a difference? Maybe tach cable or tach head?
then theres always the stethescope approach, or wooden dowel.

 

[bwringer]

Then it might be worth checking to see if the pionts heel is lubed ok.
One drop of oil on the oil wick should do it.

Yes, this.

 

[tatu]

Yes, this.

Not sure what you mean.
I had exactly the noise described when I was touring Italy 1500 miles from home. I stripped what I could (I thought it was from the clutch)
No loss of power, no rattles, not caused a major stop. It turned out that points cam was dry making a dry bearing sound that got worse.
Anyway, its cheap and easy, best do those things first.

 

[tom203]

Not sure what you mean.
I had exactly the noise described when I was touring Italy 1500 miles from home. I stripped what I could (I thought it was from the clutch)
No loss of power, no rattles, not caused a major stop. It turned out that points cam was dry making a dry bearing sound that got worse.
Anyway, its cheap and easy, best do those things first.

Yeah, he means it's a good idea!

 

[fnkvn]

Not sure what you mean.
I had exactly the noise described when I was touring Italy 1500 miles from home. I stripped what I could (I thought it was from the clutch)
No loss of power, no rattles, not caused a major stop. It turned out that points cam was dry making a dry bearing sound that got worse.
Anyway, its cheap and easy, best do those things first.

Bingo! Great call. Thats also why it had a dry, screatching sound when the engine slowed to a stop. Thanks, it sure saved me a lot of unnecessary work.