Re: compression testing

[C2slayman@domain.elided]

Modelle,
       I've often wondered the same thing myself.  There a couple of things 
to watch out for in a compression test.  1) Make sure the battery is fully 
charged.  2) Count the number of compression pulses for each cylinder and 
don't stop until the compression saturates -typically 5 to 6 pulses.  Use the 
same number of pulses for each cylinder.  3)  Hold the throttle wide open 
each time to give each cylinder an unobstructed intake flow.  4)  Do the test 
dry for all cylinders.  5)  Do the test wet for all cylinders with equal 
amounts of oil.  6)  Repeat the wet test and see how much variation you get 
from your original wet reading.
       I have found it difficult to get good repeatablity on the wet 
compression test because it does depend on how much oil you inject.  So the 
wet/dry compression test is good at telling you if you have a problem.  If 
you pass the test, button things back up and quick worrying!  If you fail 
(like you have), then the next step is a leak-down test.  Pressurize #1 
cylinder with compressed air through an adapter in the spark plug hole.  Then 
listen for leaks in the crankcase (bad rings or on rare occasion blown head 
gasket leaking through the oil passages), muffler/exhaust (bad exhaust 
valve), intake manifold (bad intake valve) or radiator (blown head gasket  
leaking from the cylinder into the water passage).

Good Luck,
Charlie


> Date: Tue, 11 Jun 2002 07:52:18 EDT
> From: GModelle@domain.elided
> Subject: Re: compression testing
> 
> Esteemed Digesti,
> I ran a routine check of my spider's 1750 compression, and found that no. 1 
> cylinder was about 50% of all the others. Then funneling about 25 cc's or 
> so 
> of motor oil into the no. 1 spark plug hole, I cycled the starter and redid 
> the test. The result:  no. 1's compression was nearly up to the same 
> standard 
> as the other three cylinders. Is this a fair test of ring condition? The 
> motor burns very little oil. How do I know the improved compression was not 
> a 
> function of the added oil volume to the combustion chamber? 
> Steeped in regard and 20W50, I remain, 
> 
> Modelle in Somers Point
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