How to check compression on outboard motor

Ensure that your battery is fully charged. The first is called a leak down test.

There are two basic ways to compression test an outboard.

How to check compression on outboard motor. How to Compression Test an Outboard Motor BoatUS - YouTube. There are two basic ways to compression test an outboard. The first is called a leak down test.

This uses a special set of gauges. To perform a leak down test you would pressurize the cylinder with compressed air. One gauge will tell you the pressure of the air compressing the cylinder.

The second gauge will show you how much pressure has been lost. Below is a 6 step process on how to test outboard motor compression. Be careful of the spinning propeller if you happen to shift or start the engine while you are setting up.

The engine should not fire and you can achieve this by pulling on the switch that kills the engine. A compression check can tell a lot about the health of your outboard engine. Heres why and how its done.

Four Stroke Engine Illustration There are four distinct phases in a four-stroke cycle. Induction compression power and exhaust. A lot can be learned by checking the engines ability to compress the gasair mixture.

Ensure that your battery is fully charged. If your battery is weak your starter turns over more slowly which will cause a low reading. Screw the end of the compression gauge into one cylinder.

Go to the key and turn the engine over for 3 to 5 seconds. It doesnt matter whether you turn it over for 3 or 5 seconds. When checking compression on outboard it is a suggested time to buy new spark-plugs and gaps.

Make sure you have purchased the correct types and then gap these according to your engines specifications. Torque the plugs using a torque wrench this will ensure they are tight without having to strip the threads. This will allow you to turn the engine over to get the results from the compression test.

Another way is to have someone turn the key over again depending on what kind of engine you are doing this on. You will need to be careful because some engines have features that will continue turning the engine over. How to - outboard compression check Probably best to post this in the outboard repair forum for your engine make.

• Get a engine compression tester - Test can be performed out of the water on the hose - Warm up the engine - remove the spark plugs - screw compression tester into one of the cylinders - crank the engine a few cranks. Crank the engine at least 4 times to complete the test. Turn the key as far as it will go in the ignition then release it.

Do this about 4 or 5 times without shutting off the vehicle at all. The engine will be running throughout the entire process. When youre done check the compression.

Older two cycle outboards especially low horsepower can run fine around 60 psi however above 90 psi is optimal. Four strokecycle engines produce much higher compression. The main thing to check is the difference between cylinder compression.

Cylinder-to-cylinder compression readings that differ more than 10 reveal trouble. If in doubt about your readings talk with your dealer to see if theyre in the ballpark. Generally readings below 90 PSI for modern two-stroke outboards indicate a problem.

Most will produce cranking compression readings in the 90 to 105 PSI range depending on the engine year make and model. Crank over the motor the same amount of times for each cylinder during testing. Zero out the gauge after testing each cylinder.

If your motor is equipped with an electric start option count the number of second. On manual or pull start motors pull the starter rope 4 or 5 times for every cylinder you test. Write down the data from each cylinder.

Perform a wet compression test if a cylinders pressure is below specifications. This test indicates whether the valves head gasket or the piston rings are at fault. If the compression gauge indicates an increase after adding the oil the piston rings are worn.

Insert the compression gauge extension and screw it in. Have someone crank the engine and watch the gauge until you reach maximum compression. A healthy engine should have 100 PSI per cylinder.

If two cylinders next to each other both have low pressure a blown head gasket is a likely culprit. If you discover you do have low compression the. As most of us know Compression is number one in importance when buying and starting to work on a unfamiliar outboard.

In my case a 2 cyl Maybe a dumb question. Your screwing in your compression gauge in one of the 2 cyls one at a time to check compression do you leave the other spark plug in while turning it over so you can. One of the best ways to check your engine is by checking your engines cranking compression because it will reveal a lot of information about your engine.

This compression check that is performed is going to tell you if your piston rings are working properly and that your cylinders are in good shape as well. Outboard blocks do crack. More often they get corrosion around the cylinder heads or exhaust water jackets and they can leave a milky oil in a 4 stroke outboard.

The valve seats are also noted for cracking in 4 stroke outboards. If it is a 4 stroke outboard forget the compression check and do a leak down check it is much more accurate. Set the throttle wide open and then pull the pull cord six or seven times to test the compression.

Next check the gauge on the compression tester. Johnsons specs are for the engines compression to be between 85 and 90 PSI so this cylinder passes. Low compression can sometimes be a result of loose or damaged parts.

An engine is constantly vibrating which can result in bolts and other parts becoming loose over an extended period of use. As part of your routine maintenance it is important to check for cracks in the engine worn gasket loosen bolts and spark plug. Like putting the control handles in the wide-open throttle WOT position.

Putting the handles in neutral and in WOT are going to open up the throttle plates and allow the engine to get more air. For a general number scale for compression. Two-stroke engines should be.

Check your owners manual under the section for compression specification requirements for your outboard motor. The psi listing in the manual will be the minimum allowable number for your engine. If any of the engine cylinders fall lower than 15 psi you have compression deficiency in that cylinder resulting from worn rings a bad valve seat.