Benz Mondi
Petty Officer 2nd Class
- Joined
- Aug 30, 2010
- Messages
- 125
I?ve done compression test on cars but not on boats with coil packs and CD units.
OK, first-time boat owner?s like me, in doing your search to see how to do a compression test without shocking yourself or causing more damage, you'll come across descriptions like "...jump the solenoid so you don't have to ground the plugs or you might damage the CD's", and "....take a good pair of jumper cables and jump the starter...". All true but not really detailed enough- at least it wasn't to me.
So here's the scoop with pictures. First purchase a $10 ?12 volt Remote Starter Switch? from Harbor Freight or auto parts store. You?ll also need a compression gauge (can be rented from an auto parts store). Might as well buy some new spark plugs if it?s been a while (here at iBoats.com or at a boat store- call ahead to make sure they have it in stock).
OK, first-time boat owner?s like me, in doing your search to see how to do a compression test without shocking yourself or causing more damage, you'll come across descriptions like "...jump the solenoid so you don't have to ground the plugs or you might damage the CD's", and "....take a good pair of jumper cables and jump the starter...". All true but not really detailed enough- at least it wasn't to me.
So here's the scoop with pictures. First purchase a $10 ?12 volt Remote Starter Switch? from Harbor Freight or auto parts store. You?ll also need a compression gauge (can be rented from an auto parts store). Might as well buy some new spark plugs if it?s been a while (here at iBoats.com or at a boat store- call ahead to make sure they have it in stock).
- Disconnect each spark plug wire and make sure you know which wire came from what plug.
- Take all the spark plugs off (note which plugs came from what cylinders so you can do some detective work based on how they look)
- Make sure that the now empty spark plug wire ends are out of the way and not in contact with anything metal.
- Put some anti-cease paste on the threads of the end of the compression gauge that you?ll screw into the spark plug hole (it will make it easier to thread in by hand). Only wind it in by hand until it?s snug. Make sure that the gauge reads ?0? every time you start a test on each cylinder. On my compression gauge set up, I can just wind the hose end first then ?quick connect? the gauge when ready
- Make sure that the boat is not in gear (the propeller can spin freely without any power)
- Attach the battery leads to the battery
- Take one alligator clip from the remote starter tool and clip it to the ignition wire terminal at the starter solenoid (in my case it was the yellow wire) and the other clip to the very thick Red power cable from the battery. NO sparks should be seen. If you do, you?ve hooked it up to the wrong wires. (See pic)
- Now just press the button on the Remote Starter tool and the motor should crank freely. Let it crank at least 5 times before you let go of the switch which stops the cranking.
- Note the reading value.
- Disconnect the compression gauge set up and repeat for the other cylinders, noting the reading for each. They should all be within 5-10 psi of each other
- When done, disconnect the remote starter, replace with new spark plugs (marine not automotive plugs in my case).
- Put anti-cease paste on the plug threads. Make sure to not get any on the end of the plug past the threads. Hand tighten only. If you feel some resistance, back the plug out right away and try again so that you don?t cross thread the plug. Once the plug is all the way in by hand (you can see the little washers on the plug get squeezed at the end) and you are certain that you have not cross-threaded the plug, use a spark plug socket to tighten one ? turn. It should feel snug.
- Re-attach the spark plug wires to the correct plugs
- Check to make sure you haven?t left anything in the motor area? Start your motor!
