Toro GROUNDSMASTER 345 - Manual (Page 19)

TORO GM 345 Ford VSG-411 Gas Engine
Notes
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17
Cylinder Leakage Test.
The cylinder leakage test can locate the following problems:
1. Leaking intake valves.
•
Air leaking from carburetor.
2. Leaking exhaust valves.
•
Air leaking from muffler.
3. Leaking cylinder head gaskets.
•
Air leaking externally by head gasket.
4. Worn piston rings.
•
Air leaking from breather or dipstick tube.
NOTE. There will always be some air leakage past the rings. Use the tester gauge to determine the severity of
the leak.
With the engine rotated until the piston is at the top of travel on the compression stroke. The cylinder is filled
with air through the spark plug opening, The leakage tester will display the percentage of air lost when the piston
is at the top part of the compression stroke.
A cylinder leakage of 25 percent or less is acceptable.
Compression Testing.
1. Make sure the batteries are fully charged.
2. Remove all the spark plugs.
3. Set the throttle to high idle and the choke in the wide open position.
4. Install an automotive type (0-300 PSI) compression gauge.
5. Using an auxiliary starting switch, crank the engine (with the ignition switch off) at least five compression
strokes and record the highest reading.
6. Normal compression should read 170 to 185 PSI depending on engine temperature and cranking speed.
7. Repeat the test on each cylinder.
If one or more cylinders read low, and a cylinder leakage tester is not available, squirt approximately one
tablespoon of engine oil on top of the pistons in the low reading cylinders.
Repeat compression test on these cylinders.
1. If the compression improves considerably, the piston rings are at fault.
2. If the compression does not improve, the valves are sticking or seating poorly.
3. If two adjacent cylinders indicate low compression pressures and squirting oil in the pistons does not
increase the compression, the cause may be a leaking cylinder head gasket between the two cylinders.