Leakdown tester homemade engine cylinder troubleshooting tool
 Cylinder pressurizing tool
If you have a cylinder in the engine that is not as strong as the rest, and you have determined that it is getting spark, here's how to make a simple tool that may aid in locating the problem. This gives you some of the functionality of a leakdown tester.
- Take an old spark plug that fits the engine, and remove all of the porcelain and the center electrode, leaving just the outer shell.
- Braze an air fitting onto the shell. Some compression testers use a hose that has a male quick release fitting on one end that is compatible with the shop air hose connector. It can be used instead of the modified spark plug for pressurizing the cylinder. The Schrader valve has to be removed first, then it's ready for use.
- Turn the engine over until the piston in the suspect cylinder is at TDC on the compression stroke.
- Insert the modified plug or compression tester hose and apply 60-80 psi air to the cylinder. Be certain not to use so much air that it turns the engine.
- With air pressure in the cylinder, look and listen:
- If you hear air bubbles, it may be a leaking head gasket. You can also remove the radiator cap and look for bubbles.
- If you hear air in the exhaust (at the exhaust outlet), it may be a leaking exhaust valve.
- If you hear air coming up through the carb (open the throttle) it may be a leaking intake valve.
- If you hear a hissing noise from the oil fill tube, or the dipstick tube, it may be a piston or piston ring problem.
This simple homemade device can save a lot of time in diagnosing a problem. Using a mechanic stethoscope can help in hearing the tell-tail hissing of a leaking valve at the exhaust manifold or header port, or at the intake manifold port. The sound transmits surprisingly well.
 Leakdown tester
There is also a tool called a "differential cylinder pressure tester" (aka leakdown tester), that operates on the same principles, but it regulates the pressure entering the cylinder, and monitors the pressure that remains, the balance being the amount of "leakdown". A GOOD healthy motor will leak less than 3~5%, more than about 10~15% is in need of repair, but as was stated above, you can listen to where it's leaking, so you know whether to go after head gaskets, valves or valve adjustment, or rings.
 Cooling system pressurizer
This homemade tool is made from a radiator cap, a tire valve stem and a rubber plug that fits the radiator ID. The rubber plug is held firmly in place by a gutted radiator cap. Air can be added by a hand pump or very carefully using a compressor. Keep the pressure at or below the original rating for the radiator cap.
- Never remove the radiator cap from a hot engine.
- Use gloves, eye and body protection when working around hot engines and cooling systems.
- Don't wear loose clothing, rings, jewelry that could get caught in moving parts or cause an electrical short circuit. Keep long hair tied back.
- Don't over pressurize the cooling system.
- Don't leave coolant where children or pets can contact it.
- Dispose of coolant properly.