1979 40 hp, head gasket replacement help

[danford1]

I have a 79 40 hp Merc outboard. It runs OK at high speed but runs on 1 cylinder at low speeds. I pulled the spark plugs after idling on one cylinder and the lower plug has water on it. I suspect a bad head gasket.
I attempted to take the head off but the lower head bolts can't be removed because they hit the bath tub case before they come out. Does this mean I have to pull off the engine just to change a head gasket? Could Mercury engineers really design it this way?
If I have to pull the engine assembly from the case, how difficult is this? Is there an on-line instruction article somewhere? Do I have to buy a service manual? If so which one?

I know this post is loaded with questions. Better to ask them all now then load up the forum with posts for each question...

Please let me know everything you possibly can. I want to get this boat back in the water ASAP.

Thanks
Danford1

 

[WillyBWright]

Re: 1979 40 hp, head gasket replacement help

Bad news. It doesn't have a cylinder head. That's just a water jacket cover. If you're getting water in the cylinder, it might be a bad exhaust cover gasket or bad lower crankshaft seal. Otherwise it's a cracked cylinder. You ask about stupid engineering? Mercury excells at that! That's why I like Mercury, and why I've never owned one. As long as Mercury makes outboards, I'll have plenty of work. For us marine mechanics, Mercury Marine = Job Security.

 

[danford1]

Re: 1979 40 hp, head gasket replacement help

Thanks for the info. I got the cover off and see what you mean - no removable head.
Now let's talk about the exhaust gaskets and lower seal. I'm going to pull the exhaust apart and look there.
If it is the lower seal, how bad a job is it to change this seal? What I would like to know is - Is the seal simply pressed in so I can replace it after pulling the power head? Or. Does the crank case need to be split to replace the seal?
Are any special tools needed to pull the power head to replace this seal?
What is the procedure to pull the power head? If you can point me to a web site for the procedure, that would be great.

Thanks
Danford1

 

[Kajun37]

Re: 1979 40 hp, head gasket replacement help

you need a service manual to do what you want to do...get a mercury manual not the cylmer or seloc's......you can find them cheap on ebay...

 

[danford1]

Re: 1979 40 hp, head gasket replacement help

Thanks. I'll start looking for one.

Cheers.
Dan