[mav6759]

Hi guys I just got a 1977 Evinrude 115, and I wanted to do compression check on it. Does anyone know what the compression reading is for this motor? Also, I was wondering if the following procedure was correct when doing a compression check on this motor. Also, why does all the spark plug have to be remove from the motor at the start of the test, is there a reason for that or will I get a false reading testing one cylinder at a time while replacing each spark plug.

1. Remove all the spark plugs.
2. Disconnect the power supply
3. Place the throttle in the wide open position
4. Turn the motor over at least 3 rotation for each cylinder
5. Check the reading

Thanks,
Mav6759

[jameskb2]

That's correct.

No plugs mean no compression on the other cylinders, which makes cranking easier and faster. Saves wear and tear on the starter. Pressure reading over 100 to 110 is good, 130 is better. More important, is that the cylinder pressure is close to even on all 4. Something like 100/105/110/105 or 120/125/125/120 too. 100/125/125/110 would be not as good, because one cylinder is over 10% different than the others.

[Ranger 330V]

I would say anything over 100psi is great...the main thing you are looking for is that all the numbers are within 10% of each other. I've heard of people running down into the 80's and be okay...mine is right between 95 and 100 and runs great. I would also think about using a spark tester...mainly safety sake. You want to make sure if you unhook the plug wires that the energy going to the plugs has a place to go. That will also give you a chance to check spark while you are checking compression. If your numbers are little low or a bit off from one another do a decarb...do a search for it on here and you'll find loads about it. Good luck!

[tashasdaddy]

agree

[mav6759]

What is the purpose of removing all the spark plugs with doing a compression test. Won't that give you a false reading. Should it be one spark plug at a time.
mav6759

[iwombat]

Removing all the plugs allows the motor to turn at an RPM sufficient for a reading on the hole you're measuring. If it doesn't turn fast enough, you don't get a good reading.

[JB]

Open throttle is not necessary.

It is a good idea to warm the engine up if possible before the check.

Turn her at least 5 turns for each cylinder, whatever it takes to get the guage to max.