115HP Mercury 1974 Compression Test

[kydaile]

Hello everyone,
I need help on how to do the testing for the compression for this 115 hp mercury v6 outboard. I actually tried to do the test this morning and the number came out as below

Cylinder # 1 70psi when it is at 1000rpm and 130psi at 4000rpm
Cylinder # 2 70psi when it is at 1000rpm and 130psi at 4000rpm
Cylinder # 3 65psi when it is at 1000rpm and 120psi at 4000rpm
Cylinder # 4 70psi when it is at 1000rpm and 120psi at 4000rpm
Cylinder # 5 70psi when it is at 1000rpm and 120psi at 4000rpm
Cylinder # 6 70psi when it is at 1000rpm and 120psi at 4000rpm
Now I do not know whether these numbers are normal for this engine or not
I also don't know if I should start the engine when I test for the compression.
Please help. Thank you for reading this message.

 

[Dave1027]

Re: 115HP Mercury 1974 Compression Test

Huh? You are supposed to have all the plugs out (wires disconnected) and test each cyl while cranking the engine. Maybe that's what you meant by "start the engine". How did you get the thing up to 4000 rpm?

 

[JB]

Re: 115HP Mercury 1974 Compression Test

You are really looking for a major explosion.

Do a search for compression testing.

 

[Dave1027]

Re: 115HP Mercury 1974 Compression Test

It just occurred to me what the OP has done. He removed one plug at a time and started the engine.

To the OP,

You are not supposed to start the motor while doing a compression test. Only crank it with the starter.

BTW, it sounds like your compression is OK. I'm glad you did not hurt yourself.

 

[kydaile]

Re: 115HP Mercury 1974 Compression Test

Thanks everyone. DAVE you are correct. I only took one spark plug out at a time. I'll check the compression again tomorrow with the right procedures. thanks again.