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Re: Compression Tests <199610091948.MAA26330@dfw-ix2.ix.netc

To: guido711@ix.netcom.com (Edward M. De Reyes)
Subject: Re: Compression Tests <199610091948.MAA26330@dfw-ix2.ix.netcom.com>
From: Berry Kercheval <kerch@parc.xerox.com>
Date: Fri, 11 Oct 1996 11:32:23 PDT
Cc: jstovall@earthlink.net (J. Stovall), triumphs@autox.team.net, kerch@parc.xerox.com
>>>Edward M. De Reyes said:
 > compression check [...]
 > 
 > 3)  Remove the coil wire from the distributor cap to keep the motor 
 > from starting.

I'd STRONGLY urge removing the low-tension lead from the coil; if you just 
remove the high-tension coil lead you will still get sparks (just not in the 
plugs) and you may have gas and air mixture spewing out of the open spark plug 
holes.

 > 6) I don't have the exact factory settings for the compression, but I seem 
 > to recall a reading of about 120 or 125 psi to be about right.  You might 
 > want to check this figure, though.

To a first approximation, take your compression ration and multiply by 15.  
Atmospheric pressure is about 15 PSI (14.8 is "normal"), so for a 10:1 ratio, 
you should see close to 150 PSI.  For an older lower compresion engine (like 
my Mk VI Bentley's 6.75:1) you'd see about 100PSI.  Now, no engine's seals are 
ever perfect, so you'll see less than that, but don't worry unless it's a lot 
less.

Also, what you REALLY want to see is a uniform series of numbers, like
        130 135 130 125 135 130
without a lot of variation; if you see one number way low:
        130 135  80 125 135 130
then that cylinder has a big problem.


  --berry

Berry Kercheval :: kerch@parc.xerox.com :: Xerox Palo Alto Research Center



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