one more how to "compression check" thread. Please help!!

[salmonee]

I'm traveling 10+ hours to look at a boat. The boat has a 115 yamaha 4 stroke 2002. This is a first boat for me and i need "DETAIL" info on how to perform a compression check. There is just too many different info floating around with grounding the plug wires or removing the "kill switch" will accomplish the same thing? Don't know if this is true or not? If you remove the kill switch, will the motor turn? I'm not using the right word there with "turn", I don't think? Anyhow, the boat is a 2002 seaswirl striper. I'm sure it has a kill switch. I also saw another post about dry and wet test, where you put engine oil into the cylinder? I thought this was a "NO-NO"? As you can tell, I need help here. The boat is located in a ghost town, and thus I may not get a mechanic to do these checks, else I would just take it to one. Like I said, the boat is way out and I'm driving there over the weekend and hopefully pulling her back. Please help. The details are what's killing me.

 

[Chris1956]

Re: one more how to "compression check" thread. Please help!!

It's real easy.

Remove the spark plugs.

Put a jumper wire on the + battery cable at the starter solenoid.

Put the gauge in the top plug hole

Touch the jumper wire to the small yellow wire of the solenoid, and the starter will spin.

Let it spin a few times until the gauge stops rising.

Note the reading.

Repeat with all cylinders.

Readings should be within 15% of each other and 100PSI plus.

 

[salmonee]

Re: one more how to "compression check" thread. Please help!!

Chris,

Your not going to make this easy are you? This is a first boat for me. I don't know what the solenoid looks like or where it is located.

All the other posts I read said to pull the plugs, stick the meter down the shaft, pull the kill switch, put the throttle at full open, crank the engine, record your readings. I need something along these lines. I'm sure, I'm forgetting something.

 

[Silvertip]

Re: one more how to "compression check" thread. Please help!!

This is a four stroke so the throttle needs to be open.
Remove the plugs as described.
Pull the kill switch lanyard to disable the ignition.
No need to oil the cylinders.
You don't stick the tester down the shaft. There are two types of gauges: One type screws into the spark plug hole. The other has a tapered rubber cone on the end that is merely held firmly in the spark plug hole. The screw in type is far superior. Just use the shortest adapter that fits the plug hole and don't over tighten it. Using too long an adapter runs the risk of the adapter hitting the top of the piston.
Have someone along that can turn the key for your if you don't know how to jump a solenoid. This is not the time to learn. Four or five revolutions of the engine should be sufficient for each cylinder. Don't for get to open the throttle fully. Most importantly, you are messing with someone elses engine. Be careful! Any mistakes can be costly.

 

[salmonee]

Re: one more how to "compression check" thread. Please help!!

Thanks for the help.

One more thing. Can you confirm that I don't need to short the plug wires to the engine, as I already pulled the kill switch?