OMC Compression testing-Alternate W?

[StillFishin']

I have done a search on checking compression and it seems that the preferred way is to:<br /> 1. Disconnect plug wires.<br /> 2. Take out all plugs.<br /> 3. Hook the plug wires up to a spark tester.<br /> 4. Check compression one hole at a time with a screw in type tester.<br /> 5. All cylinders should be within 10% of each <br /> other.<br /><br /> Ok, so what it you don't have a spark tester? What would be wrong with using any of the following ways?<br /> <br /> A. Pull the kill switch and take out one plug at a time and crank it over. <br /> B. Pull the kill switch and take all the plugs out and crank it over.<br /> C. Take all the plugs out and reattach the plug wires to the plugs, let them hang and check compression one hole at a time.<br /><br />Obviously you don't want to just remove a plug and wire and crank as the engine may fire up so I didn't list that option.<br /><br />So to set my mine at easy I'd like to see what you have to say about the above, or if you have any other thoughts, please list them also. <br /><br />Thanks,<br />Stillfishin'

 

[StillFishin']

Re: OMC Compression testing-Alternate W?

No comments so I'll trymoving it up the list.<br />StillFishin'

 

[wind knot]

Re: OMC Compression testing-Alternate W?

Just remove both plugs and leave the plug wires hang. Your checking compression, not spark, so don't worry about the spark tester.

 

[StillFishin']

Re: OMC Compression testing-Alternate W?

Thanks for the reply Wind Knot, that's what I once thought but some post a while ago said you could fry your powerpacks as they wouldn't be grounded. I don't know so that's why I'm trying to sort this out.<br /><br />StillFishin'

 

[clanton]

Re: OMC Compression testing-Alternate W?

You can do it any way you like, but if you let the sparkplugs wires dangle with key on, you are asking to buy a power pack, coils, maby not today or tomorrow, but one day. Not recommended by any Mfg. Most engines can be turned by remote starter button/jumper wire at starter solenoid, with key off, for checking compression.

 

[StillFishin']

Re: OMC Compression testing-Alternate W?

Thanks Clanton and now there is another way which I think is problably as safe as the spark tester method.<br /><br />What do you think about on a 4 cyclinder taking out one plug at a time? Since the powerpack is running two plugs wouldn't the pack still be grounded? You may not get the the engine to turn over as fast and therefore maybe a lower reading but then all holes, I would think, would also be equally as low. Just wondering.<br /><br />StillFishin'

 

[Bellboy]

Re: OMC Compression testing-Alternate W?

I'm not a marine mechanic, but am an auto mechanic and it seems to me that there are two ways to address the spark plug issue.<br /><br />Whatever you do, don't just let the spark jump to ground as it's very likely that the CDI or coils may crap out.<br /><br />Anywho, I suggest to either disable the ignition system or after having removed the plugs reinstall the wires on each plug and then ground the body (the threaded shell) to the engine. The spark will still jump the gap on the plug itself...in effect replicating the exact load on the ignition system that it would "see" when running normally.<br /><br />Don't bother trying to check the compression with just one the one spark plug removed....this is not an accurate test and the engine may accidentally start and hurt you.<br />-ANT

 

[Hooty]

Re: OMC Compression testing-Alternate W?

Method "B" in your first post.<br /><br />c/6<br /><br />Hooty

 

[Solittle]

Re: OMC Compression testing-Alternate W?

Don't have a spark testor? - - Make one!<br /><br />I took a piece of scrap alumnium about 4' long and 1" wide. I took a piece of scrap 1x3" pine of the same length. I then used a circular saw like for doorknobs and cut a 3/4 moon for each cylinder in the pine 3-4" apart. Then screw the pine and the alumnium together so that the open part of the moon faces the alumnium. Drill a small hole through the pine to the top of the moon. The hole should be small enough so that you can put a bolt through the hole and screw it down so that the end of the bolt is about 1/2" away from the alumnium bar. That then is the gap for the spark. Now attach a ground wire to the bar with an aligator clip on the end. This you will clip to the block. The plug wires go over the head of the 4" bolts. You may have to do some filing on the screw heads to get a decent contact with the plug wires (I also use rubber bands to hold it together). It is easier to make than to describe.<br /><br />You can also adjust the gap to your choosing by screwing the bolt in or out.<br /><br />Mickey mouse?? You bet!! - - But it works as good as the store bought & was fun to play with.<br /><br />Another thing - when you have all the plugs out and connected to this home made spark testor make sure that you have the muff on with a small water flow to keep the impeller lubricated.

 

[walleyehed]

Re: OMC Compression testing-Alternate W?

To SoLittle: Thank you for adding the muffs!!!<br />So many people forget there is a darn hard piece of rubber, loaded none the less, that can be ruined in 15 seconds of cranking with no water present-usually the guys replacing water pumps yearly........

 

[StillFishin']

Re: OMC Compression testing-Alternate W?

Thanks guys for chiming in. I appears that all agree that taking all the plugs out is a must. Hooty's coment that pluging the kill switch is problably the easest if you don't have a spark tester but then why would you need one and wouldn't it be just as accurate?<br /><br />I'll have to reread how to make a spark tester. Accually, I have made a spark tester in a similar fashion but using old spark plugs with the ground electode removed and mounted 1/2 in away, on a board from a cenrtal ground.<br /><br />I guess I was looking for an easy quick way to check compression with out getting out the spark tester. Hootys kill switch way seens to fit the bill.<br /><br />Thanks again for helping me sort this out.<br /><br />StillFishin'

 

[clanton]

Re: OMC Compression testing-Alternate W?

StillFishing, the packs that fire 1-6 cyinders are independent of each other, ground one plug wire does nothing for the other cylinder. Some of these methods are done, just because it is easy to do that way. I have a spark tester, so when I check the compression, I use tester to check spark at same time. All plugs removed for a plug check. Three tasks for the price of one. Now on the big loopers, sometimes you have to leave one plug in, or the starter will disengage, after one rpm of the engine. I like for the piston to come to the top at leat 4 times, if compression numbers are not up to specs with 4 turns, rings and cylinders are worn.

 

[StillFishin']

Re: OMC Compression testing-Alternate W?

Clanton, gees you made a light come on in my brain-check the compression while you check the spark. What could be more efficent? You've convinced me to do it your way. But if in a hurry then remove all the plugs and pull the kill switch.<br /><br />Thanks guys. It's been a pleasuse using this forum to get this subject figured out to me. Unless anyone has any thing else to add, I thnk I have got the compression thing under control. <br />Thanks for the note about using the muffs in the the driveway.<br /><br />StillFishin'