copper pipe knock detection

Andrew Mcleod amcleod1 at bigpond.com
Fri Jul 27 12:58:40 GMT 2001


light aircraft headphones. the ambiant noise there is huge.
----- Original Message -----
From: Axel Rietschin <Axel_Rietschin at compuserve.com>
To: <diy_efi at diy-efi.org>
Sent: Friday, July 27, 2001 9:33 PM
Subject: Re: copper pipe knock detection


> > More info on this system for knock detection please,
> > it sounds cheap and feasible.
>
> Just take a small pipe, maybe 12mm (~1/2") of sufficient length. You
squeeze
> an end over 2-3cm (~1"), drill a hole in the flat you just created and
bolt
> it somewhere more or less directly to the head casting, perhaps on an
intake
> manifold stud. The pipe has to be routed avoid contact with other parts of
> the engine. At the other end you hook up some sort of Y piece and soft
> plastic pipes, then you somehow build a 'headphone', perhaps based on the
> hearing protectors used by people firing guns, to give you some level of
> insulation against ambient noise. This works very well as long as you can
> sufficiently insulate yourself from the engine noise; you can use several
> meters if pipe if necessary.
>
> Another cheap and readily feasible approach would be to use a standard
> (piezo) knock sensor as a microphone, hooked up to some audio gear like a
> portable tape recorder, and then use an audio headphone (of 'closed' type,
> and good quality such as the Sony MDR-7506) to listen to your engine
> internals.
>
> I've found that the piezo sensor and recorder worked slightly better at
mid
> rpm mid load but the copper pipe was most effective at high speed, i.e.
the
> knock-to-noise ratio was better.
>
> --Axel
>
>
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