Who can that be knocking at my...piston?

[Toby Erkson <Toby_Erkson@ccm2.hf.intel.com>]

Jim,
I found your description of the knocking *very* helpful.  I have had this 
problem in the past and just shrugged it off as a "cooling tin vibrational 
frequency" that my engine was producing at the low RPM, high throttle 
position.  Luckily I had the good sense to stop what I was doing that was 
causing the "vibration".  Now I know what knocking (in an engine) sounds 
like.

I am assuming that pinging is similar but, of course, at a higher tonal 
frequency -- is that correct?  Could you describe what pinging sounds like? 
 I'm guessing that it would most likely occur at higher RPM and on an 
engine that is running hotter than stock.  What ya say?

     Toby Erkson
     air_cooled_nut@pobox.com
     '72 VW Squareback 1.6L bored and stroked to 2.0L
     '75 Porsche 914 stock 1.8L for sale
     Portland, Oregon, USA


______________________________ Reply Separator _________________________________
Subject: Berg and typeIII's...
Author:  type-3-errors@umich.edu at SMTPGATE
Date:    4/19/97 9:31 PM

...
I think your compression ratios sound pretty reasonable, but you don't
mention whether your engines knock or ping.  These are things everyone talks
about, but most people don't really know what they sound like.  My '68 used
to do it badly, but I didn't know what it was at the time.

Knocking is a phenomena that occurs at low RPM and full throttle.  It goes
away as the car speeds up past some point.  It really sounds like something
is rattling around back there, kind of like a loose piece of cooling tin
around the engine.  A friend once described it as sounding like dropping a
handfull of ball bearings slowly into a steel wastebasket.

If your engine pings, your CR is too high or your gas octane is too low.  If
it doesn't ping, but it still overheats, then you have some other problem.
Perhaps it's running too lean, or maybe some of the cooling tin was left off
by someone who "just knew that it wasn't important," or maybe the air intake
bellows at the rear of the engine is torn, or gone, so your engine only gets
warm air to cool itself.
...
Jim
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       Melissa Kepner                                    Jim Adney
       jadney@vwtype3.org              jadney@vwtype3.org
                             Laura Kepner-Adney
                             Madison, Wisconsin
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