How To Perform A Leak Down Test - Fast & Easy

How to Perform a Cylinder Leak Down Test

Introduction to Cylinder Leak Down Testing

• The video introduces the concept of a cylinder leak down test, referred to as a pinpoint test, following a general compression test.

• This test checks the internal combustion engine's operation by assessing air loss in the cylinder, which can indicate potential issues like misfires.

Preparing for the Test

• The process involves raising the piston to top dead center (TDC), ensuring both valves are closed for an accurate seal before introducing shop air.

• Loss of compression or volume in the cylinder can lead to engine misfires; thus, identifying whether it's due to valve problems, ring issues, or head gasket failures is crucial.

Equipment Setup

• A TDC whistle is used initially to confirm that the piston is at TDC before proceeding with the leak down tester setup.

• It's important to remove the Schrader valve from adapters when using a compression tester adapter for accurate results.

Conducting the Test

• The leak down tester measures how much air enters and what volume is lost; investing in quality tools ensures accuracy and longevity.

• Calibration of the tester is necessary before connecting it to ensure correct readings; over 80% loss indicates setup errors if no misfire occurs.

Troubleshooting and Safety Measures

• If difficulties arise during testing, manually rotating the crankshaft can help achieve proper positioning for accurate testing.

Cylinder Leak Down Test Explained

Understanding Compression Loss in Engines

• It's essential to set the gauge to zero before connecting it to the cylinder. Regardless of whether an engine is new or has high mileage, some compression loss is expected due to piston ring end gaps.

• A normal engine may exhibit up to 20% compression loss straight from the factory, while a 40% loss can still be acceptable during testing.

Conducting the Cylinder Leak Down Test

• During a leak down test, ensure that the gauge remains within the acceptable range (0-40). If it does, this indicates no significant volume loss in the cylinder being tested.

• A result showing over 80% volume loss signals a problem. The technician's task is to identify where this air is escaping from.

Diagnosing Issues Based on Test Results

• Potential sources of leaks include access points like PCV systems, oil passages, exhaust and intake valves, and coolant pathways. Checking for bubbles in the radiator can indicate a blown head gasket or cracked block.

• Observing smoke or noise from the dipstick or oil fill cap suggests issues with piston rings.

Advanced Diagnostic Techniques

• Using a glove over the exhaust can help determine if an exhaust valve is stuck open; if it inflates, there's an issue with that valve.

• Removing vacuum hoses allows for sound checks; changes in noise can indicate air escaping through an intake valve.

Conclusion and Call to Action

• If diagnosing reveals adjustable valves, further inspection may be necessary. If not adjustable, more extensive repairs like removing the head might be required.