i am doing a body-off restoration and in doubt if a engine overhaul is necessary or not...since a previous owner has done it ... my guess 15000 miles ago.  but wanna makes some checks anyway.

was planning to buy a cylinder leakdown tester ( saw some on ebay).. but haven't any experience using it.... can i simply plugg it in the sparkplug holes and put airpressure on it... or does does the piston /valves etc  need to be in a certain position or other things i should know about before buying/using such a tester?

tia

art-corvette

 

 

The piston needs to be at TDC(top dead center), on the compression stroke, meaning that both the intake and the exhaust valves are closed.
A leakdown test determines the amount, in percentage, of leakage. The gauge(s) on the tester will have the pressure(psi) going into the cyl., and the other gauge will show the percentage of leakage going out of the cyl.
You will have to determine where the air(leakage) is comming from.
You will need to listen at the exhaust for the sound of air. If you hear a large amount of air comming out of the exhaust pipe, then its a good bet you have a problem with the exh. valve.
If you hear air from the intake/carb., then you have an intake valve leak.
If you can hear air from the valve cover area. then you have a problem with the rings on that cyl.

If the leakdown test for any cyl. shows no/minor leakage, that cyl. is OK. and you won't likely hear any air escaping anywhere. What you're looking for is the same as with a compression test, an AVERAGE between all cyls.

Another method of doing the same thing is to just put the pist. on TDC, and connect the air to the cyl. You will be able to hear any leakage from the exhaust, intake, or v/cover, the same as with the leakdown tester. The difference is, you won't know how much it is leaking.

Leakdown testers are great tools for finding weak/marginal cylinders, but they do take a little experience in "reading" the results. Hopefully, any tester you buy will come with destructions on how to read the results of the test. Adams' Apple38669.3689467593

already had in mind to ask if a tester comes with a good instruction manual

already figured out myself the valve must be in closed position but maybe a silly question.. but how can i see or put a piston at TDC?

all in all it seems a helpfull test for me to see if i need to open up the engine or leave it the way it is  (only drove about 40 miles with it so can't say much about the engine beside it ran smoothly.

even though i don''t have any experience with it.. i guess i must be able to get an idea about the average between all cylinders.

art-corvette

 

 

 

Take off the distributor cap.  Turn the engine so the rotor points at a cylinder plug wire.  Follow the wire to that cylinder. Then with the spark plugs out, you can put a soft rod, wood dowel, soda straw, etc into the plug hole, and gently turn the engine back and forth and feel the piston reach the top of the stroke.  Dont use a steel rod.  You don't want to bind up and cause damage to the piston or plug hole.  Then connect the leak down tester.

thankz,  i am sure i will manage with this info to get an idea what is going on inside my engine........  and if i don't..... i will come back with more questions

art-corvette