How do i check my compression?

[birdman23]

i know this is probly a dumb question but i just bought my first boat and keep reading that i need to check and make sure compression is within a 10 point range of each other.


so is it easy to do or do i need to buy something?


i am working with a 125 force outboard 1986 bayliner


thanks

 

[gunner1]

Re: How do i check my compression?

You'll need a compression checking tool. Basically it consist of a gauge attached to a hose which is attached to a fitting which screws into your sparkplug hole. You can then bump the motor over and record the reading. It is important that the numbers be fairly close to each other, but you also want pressures over 100 psi. If the pressure on the cylinders were only 50-60 psi, your looking at some motorwork.

 

[Randy169]

Re: How do i check my compression?

I always perform a wet and dry test.

I am not familiar with outboards, but you want to make sure it doesn't start. I usually do this by removing the coil wire.

Buy a compression gauge (usually $25 or so).
The 'dry' test.
Remove the first plug and screw in the gauge. Turn the engine over a number of time and write down the highest number from the gauge for that cylinder.
Now for the 'wet' test.
Unscrew the gauge, squirt a couple of squirts of oil into the cylinder, screw the gauge back in and turn the engine over a few times.

Do this for each cylinder - one at a time. Meaning put the plug back into the engine with the wire before moving onto the next cylinder.

Each cylinder should be within 10% of each other.
The 'wet' test, tests the piston rings. If the readings are very much higher than on the 'dry' test, the rings are going. How much higher? Some people say 10%, others say 20%.

Hope this helps.

Randy

 

[birdman23]

Re: How do i check my compression?

You'll need a compression checking tool. Basically it consist of a gauge attached to a hose which is attached to a fitting which screws into your sparkplug hole. You can then bump the motor over and record the reading. It is important that the numbers be fairly close to each other, but you also want pressures over 100 psi. If the pressure on the cylinders were only 50-60 psi, your looking at some motorwork.

do i do this at idle or do i need to kick up the RPM a little?

thanks

 

[mrmushroomman]

Re: How do i check my compression?

I always perform a wet and dry test.

I am not familiar with outboards, but you want to make sure it doesn't start. I usually do this by removing the coil wire.

Buy a compression gauge (usually $25 or so).
The 'dry' test.
Remove the first plug and screw in the gauge. Turn the engine over a number of time and write down the highest number from the gauge for that cylinder.
Now for the 'wet' test.
Unscrew the gauge, squirt a couple of squirts of oil into the cylinder, screw the gauge back in and turn the engine over a few times.

Do this for each cylinder - one at a time. Meaning put the plug back into the engine with the wire before moving onto the next cylinder.

Each cylinder should be within 10% of each other.
The 'wet' test, tests the piston rings. If the readings are very much higher than on the 'dry' test, the rings are going. How much higher? Some people say 10%, others say 20%.

Hope this helps.

Randy

As stated above do not let motor turn over. Just bump it each time.