I am going to post what I think is the way to do these test.  Tell me where I am wrong.   Doing a Chevy 327 in a 1966 car. 

How expensive or good does my leak down tester need to be?  New Snap On is over $400.  Used Snap On on Ebay about $200.  ATD for $88.  Hmmmm.  

Compression test. 

Remove all spark plugs, (allows the engine to turn over easier by hand, if desired)

Cold engine or hot engine.  Should not make any difference, right ??

Hand tighten hose into first spark plug hole.  Turn over engine with starter 6-8 times.  Write down max. compression reached for each cylinder.



Leak down test. 

Turn engine over to get TDC with valves closed for piston I want to test.  Not sure of the easiest and best way to get an exact TDC.  Do not think there is enough room to get a TDC indicator screwed into the spark plug hole on this car.   Do I want to remove the valve covers so I can observe the valves to get TDC on compression stroke ? How do I determine when piston is TDC with closed valves if I do not remove the valve cover to watch the valves ?  Is it critical to have the piston exactly a TDC ?  Is a TDC whistle a good way and accurate enough to get TDC compression position ? 

My thinking was to remove the valve covers, use a small rod or wire to watch piston travel, while watching the valve to get TDC on compression stroke.  Now I am ready to do the leak down test. Yes ?

OK.  You all have told me how to get TDC with closed valves.  I now use the tester, with Schrader valve removed, use air compressor incoming air to flow into the cylinder.  If I have 100 psi coming into the cylinder what is acceptable leak reading 90 psi, 80 psi, ect.?  Engine is not new.  

It was suggested that if I have a bad leak testing, say 50 psi.  I am losing pressure in one of these areas or maybe several ways I am loosing pressure. 

(1)  Leaking past rings.  If I pull dipstick tube I may be able to feel air coming out of the tube hole. Yes?  Or is there some place else on the motor the air will be escaping from other than the dipstick tube and the dipstick tube for air flow will not be a correct measure of gas escaping ?

(2)  Leaking past intake valve. I should be able to hear the air coming back out of the carb ???  Or how do I know the intake valve could be the possible loss of air ?

(3)   Head gasket leak.  I can remove the radiator cap and see bubbles come up in the coolant.  Yes ?  

(4)  Ex valve leaking.  Hopefully my ex pipes are tight and if I put a rubber glove over the ex pipe end it will inflate. Yes ?  Or maybe go around all the ex connections feeling or listen for air.  Yes ?


How did I do ?