Turning over an old motor

[Tao of Funk]

I am going to check out a boat for sale. It has been sitting up for "a while". I intend to check the compression. Does anyone have a technique for readying an old motor to be turned over?

The last time I did this I sprayed a bunch of WD40 into both end of the motor before I tried to turn it over. Since the plugs were out when I checked the compression I had no issues with it "popping off".

BTW this is a mid 70's 85hp Evinrude, I figure I'd like to see 110 psi to 120psi and all within 5psi of one another. Sound right?

AND, does anyone have experience with compression changing (for the better) on a motor that has been sitting a while. Can the rings get stuck from inactivity and then un-stick after the motor is exercised?

I have a long list of things to check on this motor but any advice is appreciated.

 

[Pussiwillow]

Im no expert but from my experience I do the same as you, spray wd 40 in cylinders but I wait before the compression as the oil around the rings can affect the compression and make the numbers higher then they really are but a few minutes of checking other things will allow it to seap down, you will be looking for compression around 110 and up for a motor that age within 5-10 pounds within eachother of course less is better, and after sitting for awhile depending on how it was take care of the bottom rings tend to get a little stuck, usually a few decarbs frees it up there are several methods but for unsticking rings I run the motor to operating temp tilt the motor pull the first plug and bring it tdc and spray decarb in the cylinder around the rings and let sit 15 minutes put the plug back in and fire it and run for 10 minutes at fast idle, repeat for each cylinder. It takes awhile but pays off. Good luck and someone will be by and hopefully give you more things to check for that I didn't

 

[Tao of Funk]

Re: Turning over an old motor

Im no expert but from my experience I do the same as you, spray wd 40 in cylinders but I wait before the compression as the oil around the rings can affect the compression and make the numbers higher then they really are but a few minutes of checking other things will allow it to seap down, you will be looking for compression around 110 and up for a motor that age within 5-10 pounds within eachother of course less is better, and after sitting for awhile depending on how it was take care of the bottom rings tend to get a little stuck, usually a few decarbs frees it up there are several methods but for unsticking rings I run the motor to operating temp tilt the motor pull the first plug and bring it tdc and spray decarb in the cylinder around the rings and let sit 15 minutes put the plug back in and fire it and run for 10 minutes at fast idle, repeat for each cylinder. It takes awhile but pays off. Good luck and someone will be by and hopefully give you more things to check for that I didn't

Thank you!

 

[1946Zephyr]

Re: Turning over an old motor

Yep, sounds like you're on the right track. It's best to get things in there wet, before you crank it over.

Pussiwillow gave you some good pointers. Check the compression numbers again after the decarb and you run it for a while. That will tell you the true compression.

 

[paultjohnson]

Re: Turning over an old motor

I would think you would want to use something with better penetrating qualities then WD-40. A little thicker as well.. Marvel Mystery oil perhaps. WD40 is so light IMHO

 

[1946Zephyr]

Re: Turning over an old motor

Ahhh his rings aren't stuck to the cylinder walls, he's just getting some light lube around the moving parts, so they're not dry.