Okay, i'm new to the forum, and joined mainly because I cannot get a real answer anywhere, and I have had good luck with forums in the past. so here is my current situation.

I have a 1979 Mercury 40hp on my jon boat right now. the motor is in fair condition. I rebuilt the starter and got the motor to turn over, and there is good compression in each one of the cylinders. however the ignition switch box has been completely melted (not by me).

I also recently bought a 1980 mercury 40hp for parts to continue the repair of the 79. however, upon bringing the 80 home today, I have looked it over and it is much cleaner and in much better condtion than my 79. but there is a problem with it. the number one cylinder lost compression. I bought it from a boat shop and they were not positive if it was rings or a cylinder. So after looking at my 79 and the 80, I started thinking maybe I would like to use the 80 instead. So I have been trying to figure out if my powerhead components (cylinders, pistons, etc) in the 79 are compatible with the 80. I will list serial numbers below.

1979 serial #: 5253808

1980 serial #: 5661617

any help is appreciated.

what the hell?

Yeah really, I am a member of many forums and I have never seen this much crapola posts.

get used to it
they do not remove the spam

It would b easyer to keep the 79 powerhead as is and just use the 80 for the parts unless you want to spend alot of time to rebuild it. the 80 might have more wrong with it than you think.

that is what most people have been telling me. I have decided to do that. i put the CDI box and switch box on the 79 and also put the carb and both coils on and am now in the process of re-wiring the key igntion/external harness. also have to replace the rectifier.

also, i want to clarify something. on the right side of the engine (if you are facing the carb) there are 2 wires that come out from under the flywheel, one red and one white i believe and they screw onto the switch box. are those wires coming from the stator or from trigger plate? the diagrams are a bit misleading and I want to know for sure. thanks