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Old 04-07-2011, 04:12 PM   #1
Frank06 OP
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Strange noise from Airhead Valve Cover

There was a *strange* noise coming from the area of the right-side valve cover on my '81 R100RT after a ride this afternoon. It sounded like an air leak (I thought I had picked up a nail or something at first.) Is the crankcase pressurized? I quickly removed the dipstick - no change. Head gasket leaking (this was only the 2nd ride after changing pushrod tube seals)? I removed the spark plug - no change. The noise slowly died away and I never determined the source. I started the engine a couple of times but it never recurred.

Advice, hints, theories, etc. appreciated! I've never heard a noise like this before.
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Old 04-07-2011, 05:41 PM   #2
supershaft
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Have you washed your bike since you got it back together?
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Old 04-07-2011, 05:54 PM   #3
baldwithglasses
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I bet it sounded like a moaning duck. My money also says it's your crankcase ventilation valve.
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Old 04-07-2011, 06:22 PM   #4
Country Doc
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My bet is that it's something that happened when you took that side apart to do the pushrod seals. Forgot to tighten the valve adjusters/set the valves? Forgot to torque the heads? A 10mm crescent wrench rattling around in there?

I'd take off the valve cover and have a _look_ before doing anything else.

dc
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Old 04-07-2011, 06:32 PM   #5
Beater
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My bet is that one of your carb tubes has bent or become 'unsealed'. It is a sucking sound, allowing unfiltered air to go directly into the carbutators ... mine did it and I tore the thing apart looking for it, and the tube had 'crimped' underneath because I had over tightened the pipe clamp.

I do these things for the common good, in the hopes that my idiocy will serve as a warning to others.

True story.

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Old 04-07-2011, 06:42 PM   #6
Frank06 OP
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Quote:
Originally Posted by supershaft View Post
Have you washed your bike since you got it back together?

No
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Old 04-07-2011, 06:44 PM   #7
Frank06 OP
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Quote:
Originally Posted by baldwithglasses View Post
I bet it sounded like a moaning duck. My money also says it's your crankcase ventilation valve.
It was a pretty loud "hiss" sound - where is that valve? Is that what feeds into the airbox?
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Old 04-07-2011, 06:45 PM   #8
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Originally Posted by Beater View Post
My bet is that one of your carb tubes has bent or become 'unsealed'. It is a sucking sound, allowing unfiltered air to go directly into the carbutators ... mine did it and I tore the thing apart looking for it, and the tube had 'crimped' underneath because I had over tightened the pipe clamp.

I do these things for the common good, in the hopes that my idiocy will serve as a warning to others.

True story.

I wasn't clear, but the engine was not running when this happened. It wasn't a carb sound.
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Old 04-07-2011, 06:45 PM   #9
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Quote:
Originally Posted by supershaft View Post
Have you washed your bike since you got it back together?
My first thought exactly!

The first time that happened to me it drove me nuts! What happens is a well is formed between the head and valve cover near the spark plug. When the bike warms up the water boils and makes that popping hissing sound.
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Old 04-07-2011, 06:46 PM   #10
Frank06 OP
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Quote:
Originally Posted by Country Doc View Post
My bet is that it's something that happened when you took that side apart to do the pushrod seals. Forgot to tighten the valve adjusters/set the valves? Forgot to torque the heads? A 10mm crescent wrench rattling around in there?

I'd take off the valve cover and have a _look_ before doing anything else.

dc
I think you're right; I did all that but it can't hurt to double-check. I'll do it tomorrow early a.m. and report back.

Thanks for everyone's thoughts.
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Old 04-07-2011, 10:00 PM   #11
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Quote:
Originally Posted by Wirespokes View Post
My first thought exactly!

The first time that happened to me it drove me nuts! What happens is a well is formed between the head and valve cover near the spark plug. When the bike warms up the water boils and makes that popping hissing sound.
I forgot to ask if it got rained on. From the way Frank06 is describing the noise, I can't see how it is anything else. After the bike is shut off and for some time?
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Old 04-08-2011, 03:31 AM   #12
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Hmmm, now that you mention it, it did rain (quite a lot) on the first ride a couple of days earlier, but it didn't make the noise after that ride and it's been warm(er) and dry since then. And I didn't see any water when removing the spark plug; the noise sounded like it was inside.
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Old 04-08-2011, 09:47 AM   #13
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Yeah, water can collect around the spark plug indentation and then boil off. Normal when wet.
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Old 04-08-2011, 10:25 AM   #14
supershaft
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You would have to remove the valve cover to see the water. It gets trapped in that little gap right in the center of the cover between the head and the cover. I suspect this is what you are hearing. They all do that.
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Old 04-08-2011, 12:37 PM   #15
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Ah-hah. Well, I'm surprised that the water would be there after sitting around and being ridden for a couple of days but it sure sounded like that!

Nothing amiss under the valve cover and the bike runs fine (knock, knock) so we'll assign probable-cause to trapped water.

thanks everyone!
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