1984 185hp johnson compression low?

[knotoncall]

ok, what i have learned from the past when buying used motor is to first and foremost check compression, i had a mechanic buddy come by with his compression tester (an expensive tester), with the motor cold and a new battery, i took out all the spark plugs and tested each cylinder, with eight revolutions on each i am getting 85 psi on all six cylinders, i then sprayed wd 40 in all the cylinders and the compression went up to 95 psi on all cylinders, this is all before i even try to add gas and start, is this motor weak, or do i need to just spend a little money on it,(sea foam, carb clean..etc)?

 

[Joe Reeves]

Re: 1984 185hp johnson compression low?

Normal, average compression on that engine when brand new (lubricated cylinders) would be 95 psi on the starboard bank and 90 psi on the port bank. The compression you're encountering is right on, nothing to be concerned about.

However..... DO NOT be spraying WD40 into the cylinders as that solution has a cutting base. Better to spray a light oil or a pre-mix mixture.

 

[knotoncall]

Re: 1984 185hp johnson compression low?

thanks joe, i feel much better now! i hear you about the wd 40, its all i had at the time, but you live and learn...