compression test on yahama 225

[jmsims3]

How do you do a compression test on a 1999 Yahama 225 and is it something that you can do yourself? Thanks for any help!!

 

[scjmc]

Re: compression test on yahama 225

It is something you can do yourself. It is fairly easy. Get a compression tester and follow the directions. They go something like this.... Run the engine at idle for about 10 minutes. Disconnect all of the spark plug wires. Crack each plug about half a turn. Remove one spark plug at a time and screw the compression tester in. Spin the engine over a few times (4 or so), and check the number. Remove the tester and reinstall the spark plug. Repeat this for all cylinders. If its a 2 stroke motor you might want to decarb it first.

 

[JB]

Re: compression test on yahama 225

I have a slightly different set of instructions.

Preparation:
1. Get a good, screw-in compression tester.
2. Bring battery to full charge.
3. Warm the engine up.
4. Remove all spark plugs. It is not necessary to disconnect them from the wires.
5. Put gearshift in Neutral.
6. Arrange a jumper wire to energize the starter solenoid without turning on the ignition.

Test compression:
1. Screw guage into #1.
2. Turn the engine at least 5 times, observing guage reading. When the reading stops increasing, stop and record the reading.
3.. Repeat #2 on each cylinder, turning it the same number of turns as with #1.

All cylinder readings should fall within a 15% span. Do not get paranoid about psi. If your engine is sick there will be a wide spread of readings.

 

[jmsims3]

Re: compression test on yahama 225

It does sound simple enough. Thank you for the help, but I do have one more for you! Where would I find what the compression should be. I am trying to check out a motor on a boat I may purchase and friends have told me to make sure and check the compression. One of my friends has a compression gauge but says the rest is on me. I would call a mech to go check it out but it is out in never never land. Just looking for a place to start!! Thank you again for your help.

 

[scjmc]

Re: compression test on yahama 225

Like JB said dont get to paranoid about the actual numbers. The important thing is that all 6 cylinders are close in compression. For example #1 105, #2 105, #3 110, #4 112, #5 104, #6 110. That is good example since the largest spread is from 104-112 PSI. Thats less than a 10% differance. If 1 cylinder was say 90PSI then you would have a problem. You can get compression testers at your local auto parts store for about $30.