The compression number is not a published number due to several reasons (compression release mechanism, strength of pull, etc.). We use a tool called a leak down tester (part number 19545), which uses color gauges and a low-pressure air (of about 70 psi) to determine if there is any loss of compression.
The cylinder leakdown tester is placed in series with a compressed air source and the engine being tested. The crankshaft must be locked at TDC between the compression and power stroke before compressed air is introduced into the cylinder leakdown tester. The overall condition of compression components is determined by the amount of leakage after the combustion is filled with compressed air. Air continues to fill the combustion chamber until air pressure in the chamber equals the regulated supply air going into the tester. Engines normally have some combustion chamber leakage, and some air may continue to flow. An engine having satisfactory compression displays a reading in the green range on the leakdown gauge with a minimum of audible leakage. A reading in the red/green or red range, along with high audible leakage, indicates a problem with compression components.
All internal combustion engines leak some air when tested with a cylinder leakdown tester. The best way to determine the location of a leak is the audible noise from the source as it passes through any engine opening. The engine is inspected for noise with the air cleaner removed at the muffler and the oil fill dipstick or breather tube. Head gaskets, hose, and fitting should also be checked for leaks.
Compression loss can present different symptoms. For example, an exhaust valve leak can cause an engine to appear to have little or no fuel for cold starting. When the piston moves toward the crankshaft, maverick air can enter the combustion chamber through the exhaust valve. The maverick air takes the place of the air-fuel mixture drawn through the carburetor. Without the proper air-fuel mixture, the engine has an insufficient amount of fuel vapor and does not start.
With a leaking exhaust valve, an engine with less than optimal compression can sometimes be started by priming the combustion chamber. Less fuel is required to keep an engine operating than is required for initial cold starting. The engine may operate acceptably when warm, but the leaking exhaust valve still affects engine operation. Maverick air continues to enter the combustion chamber through the carburetor. The lean air-fuel mixture produces higher combustion chamber temperatures, which can cause damage to the valve train and other compression system components.
This test can be performed by a Briggs & Stratton Authorized Dealer. Your Briggs & Stratton Authorized Dealer has all the information relating to Briggs & Stratton warranty information, replacement engines, short blocks, parts, pricing, service/repair, specifications, etc.
For your convenience, we offer three easy ways to locate your nearest Briggs & Stratton Authorized Dealers:
Use our website's Service Center Locator.
Visit www.yellowpages.com and enter "Lawn Mowers" or "Engines-Gasoline" in the Category search field and your Postal Code in the Location search field.
Call the Briggs & Stratton Automated Hotline at (800) 444-7774. This hotline is available 24 hours a day / 7 days a week and features voice recognition technology to assist you in finding the Briggs & Stratton Authorized Dealers in your area. Automated maintenance tips, product information, and FAQs are also offered through voice activated menus.
If you wish to perform this test yourself, our Service Tools Catalog (PDF) contains illustrations and part numbers of our specialty tools.
Selected Service Tools can be purchased through the Genuine Parts section of our website. Service Tools can also be ordered via phone by calling our Briggs & Stratton Answer Center at (800) 444-7774 (48 Contiguous United States orders only).
In addition, selected Briggs & Stratton Authorized Dealer also sell Service Tools. Please contact the dealers in your area to determine if they offer this service.
Please read and abide by any applicable Safety Information contained in your engine Operator's Manual. The material provided above is not intended to replace work performed by a Briggs & Stratton Authorized Dealer. Terms and Conditions apply to all of the information presented on this website. Always be sure to completely read and understand your engine Operator's Manual.
