Testing compression

Finally I got the meter for testing compression.. My boat has a "deadmans" switch on dashboard. Functions so that if you are hooked to it and drop to water etc. the engine stops. When I check the compressions do I need to ground the sparkleads, or is it ok to test them when the switch is of? Coils have two wires coming in. Engine is Force 120hp year 1992.<br /><br />Thank you for your help again,<br />-Jaba-

Re: Testing compression

First, do ground the spark plug cables or a spark could ignite fuel vaporized and expelled from the other cylinders or from the carburetors.<br /><br />Secondly, use a two tiered approach doing a dry measurement and a wet measurement putting some TCWIII oil in the cylinder being measured.<br /><br />Thridly, get an owners manual.<br /><br />Finally, the compression test will not evaluate the primary compression. As two stroke motors are "pumps" when the piston comes down it compresses the fuel/oil and air mixture previously before opening the transfer port.<br /><br />If the seals, retainers, etc., are damaged the primary compression could be the culprit of operating problems.

Re: Testing compression

Here is a thread on testing compression. Hope it helps. You should have the motor in water and warm when you test it. I believe you have to disable the neutral safety lock because you need to do the compression test at full throttle and you will not be able to turn it over unless you disable it.<br /> compression test

Re: Testing compression

Here is what my manuals recommend. Warm up the motor. Disable the ignition with the kill switch. Take all the plugs out. You can ground the plugs for extra safety, if you want to be really cautious. Have the throttle opened fully. Using a remote starter switch, connected to the positive wire at the starter and to the thinner wire going to the ignition, turn the motor over 4-5 times for each cylinder. Write down the readings. If you do not have a remote starter, ask a friend to help you by turning the ignition switch. If you are concerned about damaging your impeller, continue with the earmuff water source -- on land. That should do it. More than 15 psi difference between/among cylinders is considered too much. If a reading is too low, spray some oil mist in the cylinder, for a "wet compression test." If the pressure increases, your problem may be stuck rings due to carbonation -- solved by decarboning. If the wet test does not help -- get your wallet out -- $$$$$$$$$. Good luck.

Re: Testing compression

Hi folks again,<br /><br />tested the compressions and for my relief, there was not too much varience, or what do you think of these: 1.(under flywheel) 7bar, 2.)7,4bar 3.)7,6bar 4.)6,8bar. Tested with cold engine by startmotor and fogoil. Don´t have a possibility to warm the engine up in yard.. <br /><br />-Jaba-

Re: Testing compression

Jaba. What is a bar? I believe it is a measurement for the movement of murcury using pressure. Not sure what those readings mean. We use pounds per square inch. Can you give a measurement conversion to pounds per square inch?

Re: Testing compression

Eurolarva:<br /><br />Bar is a metric measurement of atmospheric presure. 1.9 bar is equivalent to 32 psi.

Re: Testing compression

At that conversion rate, the results are 118, 124, 128, and 114 psi. No grater variences then the 15 points "allowed." What are the specifications for your motor? It looks fairly good though -- without knowing the specifications.

Re: Testing compression

The numbers look good. If you decarb motor and test it again when it is warm I bet you will see higher numbers.

Re: Testing compression

Sorry,forgot to convert..I´m planning to decarb the engine once I get it to lake,ice has almost melted. The reason I started to measure compression was two sparkplugs that were shiny like new after a few hours of driving.Engine idles and runs great and gives high RPM´s. Now I know the compression is not the problem if it even exists.. Dunno, got any ideas that I should check?

Re: Testing compression

I don't think you'll have a problem warming up in your yard . Just use a garbage can filled with water and a running hose to keep it filled. Just don't put it in gear-lots of water all over the place. I've done it more than once . You also might want to think about using a 24-1 mixture for an hour or a tankful.

Re: Testing compression

Actually 1 bar is 14.5 psi, So 32 psi would be 2.2 bar not 1.9<br /><br />1 psi = 0.06895 bar<br />1 bar = 14.50326 psi<br /><br />You motor's compression in psi is:<br />1) 101.5<br />2) 107.3<br />3) 110.2<br />4) 98.6