compression test question

[skip4926]

I was reading a few posts about Comp testing.

I am unclear regarding the grounding of the spark plugs. My ignition does not have a lanyard. How do I ground the plugs to avoid ignition damage.

Do I remove all plugs for head and also wire, or keep the plugs in the wire but out of the head?

Thanks guys.

 

[westexasrepublic]

Re: compression test question

Put the plug boots on bolt heads attached to the motor

 

[skip4926]

Re: compression test question

So, remove all plugs from head then insert bolts into plug boots and attach bolts to motor for ground.

Is it safe to key ckank then?

 

[saumon]

Re: compression test question

You'll get a better, more accurate reading if you remove all plugs from the head. Grounding is done with a wire(s) with alligator clips on both ends. One onto a bolt head on the block and the other on the sparkplug end, wich is still on the boot. That way:

1- you won't damage your electronics (like coils)
2- you won't experience a ?fireball? (fuel/oil mix thrown in the air by the sparkplug hole while cranking and ignited by an ungrounded sparkplug lead)

 

[SC1650]

Re: compression test question

Please explain to me how you would damage the electronics by not grounding the plug wires. I have been doing automobiles for years and have never grounded a plug wire yet when checking compression on the engine. In fact I just checked the compression on my 7.5 horse and did not ground the plug wires and both coils are fine. Am I missing something here or is everyone just being over cautious????

Steve

 

[skip4926]

Re: compression test question

saumon,

What an awesome, detailed reply.

Thanks,

no fire balls wanted here!!!!!!

 

[bently]

Re: compression test question

It is a difference from a "closed" and "open" ignition system. Marine outboards are like PWC's "closed ignition system" the charge or sprak needs to be grounded through the block or your coil will be overcharged and burn out. Yes, you can do it without grounding your plug wires but repeated over and over, then you will have a problem.

 

[skip4926]

Re: compression test question

I take it with grounded spark plugs i can keep ignition in tack and crank with key?

 

[westexasrepublic]

Re: compression test question

aLSO UNHOOK YOUR FUEL LINE AND YES YOU CAN KY CRANK FOR A FEW SHORT TURNS

http://www.themarinedoctor.com/CandS.wmv

 

[Bill Kilgore]

Re: compression test question

Fire extinguisher is your friend.
Fire extinguisher is always handy, with visual confirmation by me, whenever I do compression test. If you have to say to yourself "I wonder where that thing is?" It could prove to be a bad day.

Just my two cents

 

[scottkell]

Re: compression test question

Why not just kill the ignition by pulling out the safety lanyard. You can crank it all day long with no ignition.

 

[saumon]

Re: compression test question

It may help to read the OP question: he say he doesn't have a lanyard.

My ignition does not have a lanyard. How do I ground the plugs to avoid ignition damage.

 

[sschefer]

Re: compression test question

CDI sells the right tool for this job. It's a pre-made unit that simply plugs into the plug wires with a double ground system. You can use it to do what you need to do and whenver you need to check spark. I hesitated to buy one thinking I would only use it once or twice. I can't even count how many times I've used it now... Well worth the investment.

 

[skip4926]

Re: compression test question (Thanks)

Re: compression test question (Thanks)

Thanks everyone for the comments. Well here are the results...

Got to the boat and again no start and lots of gas in the water

I did the compression test (cold) and got 95 on all 3. At that point I lowered the engine back down and, what do you know, it started right up. hmmmm.. Never thought the compression test would solve the problem. lol Well at that point i noticed another leak in the fuel line between the top and middle carp. Replaced that and it ran well. I also did the decab and it now starts up without juicing it.

I did realize that the decarb process is not really meant to do in the water because it does creat quite a slick around my boat. Is that gas or just carb junk that comes out.

THanks again.