How to check compression on outboard

The first is called a leak down test. I am planning to do a compression test for the first time on my 1996 Mercury 150hp 2-stroke outboard.

Generally readings below 90 PSI for modern two-stroke outboards indicate a problem.

How to check compression on outboard. 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.

Also using the spark checker not only grounds the ignition leads to prevent ignition problems from occurring during your compression check. It allows you to visually check your engines spark as you crank it. Screw your compression gauge into the first cylinder.

Make sure that the plug leads are well clear of the flywheel or any moving parts. Since youre getting low compression youll want to pull the head off and inspect it. Check the head gasket at that time to ensure its still making a good tight seal all the way around.

Ive seen a lot of people throw outboards away over a head gasket because they thought the engine was blown. How Do You Do A Compression Test On An Outboard Motor. Performing the compression test is actually a pretty simple process.

You are going to want to take off any of those covers that we talked about earlier from over the top of the ignition coils. Once you are looking at. 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. Attach the compression test adapter into the cylinder nearest the front of the engine then connect the gauge to the other end of the adapter hose. To perform the test crank the engine 4 times by turning the key in your cars ignition then check the compression gauge for the result.

This video shows the process of checking the compression on you boats outdoor motor. Below is a 6 step process on how to test outboard motor compression. Step 1 Be careful of the spinning propeller if you happen to shift or start the engine while you are setting up.

A wet compression test will temporarily seal the piston rings and possibly raise the compression. Obtain a can of fogging oil and spray the perimeter of the cylinder walls and pistons. After the oil has been applied retest that cylinder.

If the cylinder compression pressure increases the piston rings are sticking. 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. 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. 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. How to check compression on outboard Besides obvious things like blown head gaskets etc the next most common thing contributing to low compression in an outboard is leaking or misfit due to wear of the piston rings and cylinder walls.

In order to have good compression piston rings must be free in the piston ring groove to expand against. 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. When checking compression on outboard gas engines it requires compression an unobstructed exhaust compression spark fuel and air. This needs to happen in the correct amounts and at the correct time.

When the piston travels in an upward and downward direction inside the cylinder piston rings will seal against the walls of the cylinder so. I am planning to do a compression test for the first time on my 1996 Mercury 150hp 2-stroke outboard. I have read many posts in this forum on compression testing and they mostly agree that it is important to properly ground the wires to avoid damaging the electrical system.

It is not clear to me however how to properly ground them. How to Read Outboard Compression Test Results. Check the service manual on your outboard for the precise specifications.

Remember that if your engine is cold the results will be slightly lower. Good results for a two-stroke engine are between 110 and 130 PSI. 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.