Testing Compression: '73 Sportwin

[P51D]

I'm considering purchasing a 9.5 hp Evinrude Sportwin. The model number is 9322B, and the serial number is J 07865. These iboats forums have been a GREAT help in getting me up to speed on outboards, so THANKS!!<br /><br />I plan to do a compression test before buying the engine. I've heard that, at least for some engines, it can be bad to have the spark plug leads disconnected from the plugs while cranking the engine (pull starting in this case).<br /><br />1. Will it hurt the ignition system on this engine if I just remove the leads and plugs, go to WOT, and perform the test?<br /><br />2. Even if it doesn't hurt this particular engine, does it indeed cause damage on other types of engines, and what class of engines are those (e.g., electronic ignition, electric starte, etc.)? What kind of damage? Or is this just a myth?<br /><br />3. I'm guessing that a '73 doesn't have a dead man's switch/lanyard. If not, how else could I disable the ignition system to prevent harm, if that is an issue?<br /><br />4. When people refer to "grounding" the spark plug leads, does this mean you can ground the lead itself directly to the block, or do you need to do it through the spark plug, or does it matter?<br /><br />5. I've heard that I should look for 5 - 10% max difference between cylinders. Any guidelines on min psi values? Does the fact that it is a pull start, vice electric start, affect the values? <br /><br />THANKS

 

[jfm1]

Re: Testing Compression: '73 Sportwin

when you do a comp. test you only need to pull /crank about 5-6 times to get a reading depending on your gauge with the plugs removed can't hurt anything to do a spark test you can place a bolt in the sparkplug lead place appox. 7/16 / 3/8 in. from the block spark should jump to ground again wont hurt anything your not cranking it all day only looking for spark good luck

 

[Paul Moir]

Re: Testing Compression: '73 Sportwin

Not a problem on this '73 as it doesn't have electronic ignition (look for a large, easily accessible black plastic box on ones that do). So just leave them dangle.<br />I like to ground out the plug wires or short out the kill switch on outboards with electronic ignition. Grounding is simply wiring them to the block somewhere handy. If you want, you can employ the spark plug to do it.<br />I've never lost a powerpack leaving them dangle, but I don't aim to find out either. Some outboards even have handy posts cast into parts of the block for you to stick the spark plug boots on. When you leave them dangle, the voltage the plug coil generates can get *very* high, causing the ignition coil to arc over internally and send a lightning bolt down to the powerpack. Many powerpacks don't seem to be designed to take that sort of abuse as autopsys of them have revealed no protection against it. I strongly suspect the outboards that rarely have failed powerpacks employ protection (Yamaha, tohatsu for example).<br />On the 9.5s you want to see more than 60psi. Around 100 is getting pretty good. But gauges differ so keep that in mind. Throttle position hardly matters (unlike 4-strokes).