Stethoscope Question

[David Carter]

I finished my Omni 10 build a few months ago, and I've been meaning for some time to do a good job of checking it over for air leaks. Well, after reading several posts which recommend using a stethoscope, I headed to Harbor Freight yesterday and bought this one.

Today I pulled it out of the package, started up a 30hz test tone through the O10, and proceeded to probe around for air leaks. I didn't hear anything that sounded like it might be a leak, so I was happy UNTIL I got to the jack plate and I could feel a slight breeze with my finger. I probed over the area at least ten times with the stethoscope trying to hear something, and I couldn't hear a thing.

Being somewhat disappointed that I couldn't pinpoint the exact location of the leak, I started taking a closer look at the stethoscope. I had assumed that the long probe on it was a hollow tube that would allow the air to be heard as it passed through. What I discovered instead was that it's a solid rod. I can understand how this could work for detecting vibrations in an engine block, but how on earth can you find the source of an air leak using a stethoscope with a solid rod for a probe?!

Did I get the wrong thing? That was the only stethoscope they had, and I know I've seen references to a cheap Harbor Freight stethoscope before in discussions about detecting air leaks.

[Sydney]

You got the automotive stet. ( for engine tappet noise ) more of a vibration detector.
Shade tree mechanics used to use long screwdrivers placed on the valve covers and listen for tapping
The Medical ones I am familiar with have a bell-like diaphragm attached to hollow tubing. Like a horn in reverse ( the old fashion ear trumpet )
RE:
http://www.medphys.ucl.ac.uk/teaching/u ... steth.html

[David Carter]

You got the automotive stet. ( for engine tappet noise ) more of a vibration detector.
Shade tree mechanics used to use long screwdrivers placed on the valve covers and listen for tapping
The Medical ones I am familiar with have a bell-like diaphragm attached to hollow tubing. Like a horn in reverse ( the old fashion ear trumpet )
RE:
http://www.medphys.ucl.ac.uk/teaching/u ... steth.html

Yes, the one I got is a mechanic's stethoscope. If that's not the right thing, could someone who has the right kind post pics and/or links to a U.S. source for what I should have purchased?

Thanks.

[Bill Fitzmaurice]

I probed over the area at least ten times with the stethoscope trying to hear something, and I couldn't hear a thing.

All you need is a 3/8" ID rubber tube. The reason for using a 30Hz tone is because it is so hard to hear, but the air it causes to move is fairly easily heard and localized.

[David Carter]

I probed over the area at least ten times with the stethoscope trying to hear something, and I couldn't hear a thing.

All you need is a 3/8" ID rubber tube. The reason for using a 30Hz tone is because it is so hard to hear, but the air it causes to move is fairly easily heard and localized.

Thanks, Bill. I think I have some tubing laying around that I can use. Can you shed any light on the stethoscope question? Am I correct in my assumption that the mechanic's stethoscope with the solid rod probe is not the right tool for detecting air leaks?

[Sydney]

Hop up your hose with a small cheap plastic funnel.
( It's amazing how many google hits for making a stethoscope. )
PS When not in use as a stethoscope you can use it as a "beer bong"

[David Carter]

Hop up your hose with a small cheap plastic funnel.
( It's amazing how many google hits for making a stethoscope. )

Good idea. Thanks.

[Murgo]

Also, you could modify your mechanics stethoscope by removing the probe, the piece it attaches to and the diaphragm in the other end of the probe, then use the part the diaphragm used to be in as the funnel or horn. This provided the stet can be dissassembled like mine.

[David Carter]

Also, you could modify your mechanics stethoscope by removing the probe, the piece it attaches to and the diaphragm in the other end of the probe, then use the part the diaphragm used to be in as the funnel or horn. This provided the stet can be dissassembled like mine.

What I ended up doing was taking it apart so that it was just the earpiece with two rubber hoses attached to it. Thanks.