PSI on compression test

[AlfaNeely@domain.elided]

     The results of compression testing depend on a number of factors, so absolute numbers cannot be given.  For example, long duration camshafts can make a healthy engine show very low numbers on a compression gauge.
     As a rule of thumb, I figure any cylinder with less than 100 pounds is sick.  If compression is above 140 pounds and within 10% from highest to lowest cylinder, then that is pretty good and the engine is probably healthy.  Compression around 160 and even between cylinders would be even better.
     If any cylinder is low, squirt motor oil down the spark plug hole.  If the compression comes up, then the rings are bad.  If compression does not change with oil, then the valves are bad.
     Do make sure you hold the throttle open while performing the compression test.  I also like to have all four spark plugs out so that the engine turns faster during the test.
     Make sure to record the cylinder readings in a permanent record.  Then you can track the engine's wear over time.  
Ciao,
Russ Neely
Oklahoma City




In a message dated Tue, 08 Oct 2002 19:36:43 +0000, owner-alfa-digest@domain.elided writes:

> Date: Tue, 08 Oct 2002 14:28:47 -0400
> From: "Heikki Rinta-Koski" <hrk951@domain.elided>
> Subject: PSI on compression test
> 
> Hi everyone,
> 
> I'm a newbie on this list looking for Alfa as a project car/daily driver.
> 
> What kind of readings should I expect from compression check when I go and 
> see possible candidate for future toy.
> The car is Alfa Spider -76 with reconditioned head and only 
> 56000 miles.
> With weber conversion if that matters.
> I believe compression ratio should be 9:1, am I correct?.
> 
> Heikki Rinta-Koski
> Atlanta
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