Low compression?

[keithmylum]

On My 40 hp mercury when I pull the cord it feels like it is binding up. A guy gave it to me it had been sitting in a barn for the last 13 years. I want to lube the pistons a little and see if I get better compression. Right now all I get is 35psi. What is the best way/ easiest way to do this? I have the electric start disconnected. The stator was corroded.so I just want to make sure I have good compression before I start buying expensive parts.thanks it is a 1971 mercury 400m.

 

[MercBlackMax1]

Re: Low compression?

On My 40 hp mercury when I pull the cord it feels like it is binding up. A guy gave it to me it had been sitting in a barn for the last 13 years. I want to lube the pistons a little and see if I get better compression. Right now all I get is 35psi. What is the best way/ easiest way to do this? I have the electric start disconnected. The stator was corroded.so I just want to make sure I have good compression before I start buying expensive parts.thanks it is a 1971 mercury 400m.[/Q

I dont think lubing up the pistons it going to do much for your compression. take the heads off and have a look at the pistons and see if its all banged up. If you really want to lube up the pistons take off the spark plugs and spray premix in the hole and turn the flywheel.

 

[chum1]

Re: Low compression?

good idea to verify compression like what you were doing, make sure the comp testor is good, might try squirting straight 2 cycle oil in cylinders or maybe a product like marvel mystery oil to unstick rings if hopefully that is the prob., look at a parts diagram before you go yardin bolts off the engine you may find there is no "head" to pull but instead a water jacket cover.

 

[CharlieB]

Re: Low compression?

Have you checked the gear oil yet?

Drop the lower unit to check the water pump and re-check the motor to see if it turns freely. Occasionally we find a problem in the lower that the owner thought was a 'tight spot' in the motor.

Compression testers very in quality, tho 35 is way low I would still verify that reading with another gauge. If the second gauge also reads low then remove the exhaust side cover to inspect the rings and cyl walls.

 

[Texasmark]

Re: Low compression?

On My 40 hp mercury when I pull the cord it feels like it is binding up. A guy gave it to me it had been sitting in a barn for the last 13 years. I want to lube the pistons a little and see if I get better compression. Right now all I get is 35psi. What is the best way/ easiest way to do this? I have the electric start disconnected. The stator was corroded.so I just want to make sure I have good compression before I start buying expensive parts.thanks it is a 1971 mercury 400m.[/Q

I dont think lubing up the pistons it going to do much for your compression. take the heads off and have a look at the pistons and see if its all banged up. If you really want to lube up the pistons take off the spark plugs and spray premix in the hole and turn the flywheel.

Lower hp Mercs didn't have removable heads; water jacket cover, but not head...integral part of block casting.

 

[Texasmark]

Re: Low compression?

If your can get it to run, or even if you can't you might limber things up so that you can get her to start by doing the "Decarb" process outlined many times in the archives. May help "fix what ain't broke".

If you do as Charlie suggested, while you have the cover off, get yourself a can of Sea Foam and douse the rings and pistons real good with it and let it soak overnight. Then if things are as they should be....no mechanical damage observed during your inspection, gas her up and fire her up if you can. But read the decarb process anyway as there is more to it.

Mark

 

[keithmylum]

Re: Low compression?

H

If your can get it to run, or even if you can't you might limber things up so that you can get her to start by doing the "Decarb" process outlined many times in the archives. May help "fix what ain't broke".

If you do as Charlie suggested, while you have the cover off, get yourself a can of Sea Foam and douse the rings and pistons real good with it and let it soak overnight. Then if things are as they should be....no mechanical damage observed during your inspection, gas her up and fire her up if you can. But read the decarb process anyway as there is more to it.

Mark

thanks for all the replys! I squirted a little sea foam in the spark plug holes, and tried the pull rope again, same thing gets to a certain point then feels like it is binding up. I decided to bypass all the electrical and hit my starter direct to see if it would turn. When I did that, at first it acted like it did not want to go, then it turned over. I think if I had everything else hooked up, it would fired up. I have 130 on one cylinder and 125 on the other. thanks again y'all! I am going to drop the lower unit now. When I have it in gear I can spin my spindle with my hand both ways. So there is something going on down there too. My control cable need to be adjusted to because neutral is actual 15 degree backwards/reverse. Very happy it turns freely.