Tech Tip: Performing a Leak Down Test (Video)

Longacre's Leak Down Tester is available in our online store here.


Welcome to Crate In this tech video, we’re performing a leakdown test on a GM 604 engine.

The tool we are using is Longacre Racing Products Leak Down Tester.

We’ve already taken some preliminary steps to prepare. We’ve removed the valve covers, and taken off the rocker arms and the push rods on the cylinder we are testing.

We’ve also connected a line to the spark plug hole. This is the line that comes with the leak down tester. We suggest using a bit of anti-seize on the threads.

As you can see, we’ve already connected an air line to the other side of the tool. Now we’ll want to connect the other end of the line to the tool.

The air pressure from your compressor needs to be more than 100 psi. With the air line connected, adjust the dial on the tool until the air pressure is exactly 100 psi.

With that setting done, we can look at the other dial to see the percentage leak down. In this case, we have a 6-7% leak down. All engines are going to be different, but, in a new race engine, we can typically expect to see about 1 to 10 percent leak down. A great practice is to test your engine when it is new to set the base line. Then you can test it periodically through the season for comparison.

Longacre’s Leak Down Tester is available in our online store at in the Tools section. Check out our website for more tech tips and products, and be sure to subscribe to our YouTube channel to see the latest videos as we post them. Thanks for watching.