How do you perform a compression check?

Hello,

I have a 1997 Force 75 HP motor and I want to check the three cylinder's compression. What is the procedure to do this? I know that you need a compression guage. I know that you remove the plugs and push the throttle to Wide Open Throttle, and test one cylinder at a time but I do not know what else you are doing. Are you turning the key? How do you ground the plugs? Do you just place them against the head? I have done a search but have not come up with a step by step procedure.

Thanks and may the Force me with us all,

Donald

Re: How do you perform a compression check?

Well let me help you out there Mr. dst',
I'm no expert, but I have done this before. First check to see if any instructions came with your compression guage and read it. Generally you want to remove the spark plugs and set them aside, they are not part of the process. Make sure your coil wires are safely away from metal so they don't arc while you turn the motor over. Now install the compression guage to one of the spark plug holes. With the throttle open for maximum intake, turn the key and allow the engine to turn. You should see the guage start to go up. When the needle on the guage won't go any further, you have your reading. Go on to the next cylinder. Hope this helps, I'm sure you'll get some expert replies.

Re: How do you perform a compression check?

You should remove the lanyard /clip from the safety kill switch. This will prevent any spark from the plug wires. Or, ground the plug wires to the block if you have no kill switch(on the dash should be where it is located). Damage to the coils may occur if the spark is not allowed to flow and disperse.
Use the "search forum" option, there are several threads here pertaining to this subject.
Also, if you don't already have one, find a repair manual if your going to do much repair work yourself. That is a must!

Re: How do you perform a compression check?

This is good info. Mods, please sticky this thread in "how to" forum.

Re: How do you perform a compression check?

Thanks Guys,

Sounds easy enough. I have not purchased the guage yet so I will also check for instruction once I pick one up. I do not have lanyard since my motor in on a pontoon boat.

Sounds like I need to keep the plugs connected to the wires and lay them all against the block, but keep them isolated from each other.

Thanks alot.

Donald

Re: How do you perform a compression check?

Some compression testers come with extensions. You want to make sure that the end you screw into the cylinder does not have a farther reach then your spark plugs do. Most gapless plugs are 13/16 inch reach. You can compare the spark plug to the compression tester to verify you do not go beyond the reach of the plug. It is also recommended that the engine be warm.

Re: How do you perform a compression check?

Euro,

Great Tips !!!!! Thanks a lot. It could be bad if I screwed the tester in too far and the piston hits. I am using gapless plugs.

This forum is great !!!!!

Donald