Section 3 Troubleshooting Compression Test A compression test is best performed on a warm engine. Clean any dirt or debris away from the base of the spark plugs before removing them. Be sure the choke is off, and the throttle is wide open during the test. Compression should be at least 160 psi and should not vary more than 15% between cylinders. holding tool onto the crankshaft and adjust the set screw to fit in the key slot. Install a 3/8" breaker bar into the square hole of the holding tool, so it is perpendicular to both the holding tool and crankshaft PTO. If the flywheel end is more accessible, you can use a breaker bar and socket on the flywheel nut/screw to hold it in position.
You may need an assistant to hold the breaker bar during testing. Cylinder Leakdown Test A cylinder leakdown test can be a valuable alternative to a compression test. By pressurizing the combustion chamber from an external air source you can determine if the valves or rings are leaking, and how badly. If the engine is mounted in a piece of equipment, you may be able to hold it by clamping or wedging a driven component. Just be certain that the engine cannot rotate off of TDC in either direction. Cylinder Leakdown Tester (see Section 2) is a relatively simple, inexpensive leakdown tester for small engines.
The tester includes a quick disconnect for attaching the adapter hose and a holding tool. 4. Install the adapter hose into the spark plug hole, but do not attach it to the tester at this time. Leakdown Test Instructions 1. Run engine 3-5 minutes to warm it up. 5. Connect an adequate air source to the tester. 6. Turn the regulator knob in the increase (clockwise) direction until the gauge needle is in the yellow “set” area at the low end of the scale. 2. Remove spark plugs, dipstick, and air filter from engine. 7. Connect tester quick-disconnect to the adapter. Note the gauge reading and listen for escaping air at the carburetor intake, exhaust outlet, and oil fill/dipstick tube. 3.
Rotate crankshaft until piston (of cylinder being tested) is at top dead center (TDC) of compression stroke. You will need to hold the engine in this position while testing. The holding tool supplied with the tester can be used if the PTO end of the crankshaft is accessible. Slide the 8. Check your test results against the table below: Leakdown Test Results Air escaping at oil fill tube .................................................................. Defective rings, worn cylinder walls, or blown head gasket. Air escaping from exhaust outlet ....................................................... Defective exhaust valve/improper seating.
Air escaping from carburetor inlet ..................................................... Defective intake valve/improper seating. Gauge reading in ‘‘low’’ (green) zone................................................ Piston rings and cylinder in good condition. Gauge reading in ‘‘moderate’’ (yellow) zone.................................... Engine is still usable, but there is some wear present. Customer should start planning for overhaul or replacement. Gauge reading in ‘‘high’’ (red) zone .................................................. Rings and/or cylinder have considerable wear. Engine should be reconditioned or replaced.
Cooling Leakage Test A pressure test can be performed as a simple means of determining whether the cooling system may have a problem. The test procedure, possible results, and recommended corrective action are covered in Section 7. 3.4