1955 Mercury Mark 40 Help

[JDusza]

Hope you're well. Been a little while.
I have come across a 1955 Mercury Mark 40, serial 825853, and have several questions. I'm sure you can help me. Pictures attached.
4-cylinder, 2-carburetor. It was mentioned to be an "H", for high rev (?). How would I verify that?
The information I have found so far indicates 25 horsepower sometimes followed by a plus sign. What is the horsepower of the 4-cylinder? What is the horsepower of the 4-cylinder "H"?
Should I stick with straight 30 weight as directed on the plate or switch it over to marine 2-stroke oil?
Is a way to attach a dollar value? If I decide not to keep it ...
Glad I found it but I have a lot to learn about it. As always, any help and direction is appreciated.
Thanks,
J

 

[racerone]

The H is the racing version.-----Racing lower unit.----Hold on to it !!

 

[merc850]

Do not use 30w motor oil just use Marine oil at 25:1.

 

[JDusza]

Thank you.
Is there any particular place to get a copy of specs?
J

 

[Faztbullet]

Do not try to use this on any other boat other than a Hydro....

 

[merc850]

Another thing use Lubriplate 105 in the gear case not gear oil. Here's a part source including the factory manual.

Mark 40H

OldMercs.com is your one stop shop for all Mercury parts. We stock parts from 1940 to the present.

www.oldmercs.com

 

[jimmbo]

That lower unit is the Quicksilver version, for racing, which is why Fastbullet stated "Hydro only"
The stock lower unit, is quite a bit different

 

[merc850]

From a catalog, here's a site that deals in older motors and in the general forum they are talking about a KF9 (early Mark 40). Do you have the fuel tank?

JohnsOldMercurySite - Index page

johnsoldmercurysite.com

 

[merc850]

Here's another description of the "Quicksilver"

 

[racerone]

Use this motor on a racing type boat.----Or sell it on E-bay.-----Best chance to find a few eager bidders on this motor.----Collecters will pay amazing beer tokes for one of these.

 

[JDusza]

Thank you, all. Great information. Might have to build another boat....lol.
I have neither the tank nor the fuel line but I look forward to learning more and perhaps a little shopping.
J

 

[Scott Danforth]

Before 2stroke oil existed, sae 30 was mixed with gas for 2-strokes.

However there is less carbon buildup with today's synthetic 2-stroke oils than SAE 30

 

[jimmbo]

Even the Non-Synthetic TCW-3 Oils are pretty good at reducing Carbon Buildup. Far superior Lubrication in a 2 Stroke than plain old SAE 30.

 

[Willyclay]

The information I have found so far indicates 25 horsepower sometimes followed by a plus sign. What is the horsepower of the 4-cylinder? What is the horsepower of the 4-cylinder "H"?

Mr. K was known to be a little vague about the "rated" horsepower of those beautiful old Mercury motors. He always wanted to be faster than the other guys for a particular horsepower. The difference seems to have been how many revs his could turn. Hope you share more info. Good luck!

 

[Scott Danforth]

Carl was know to rate his early motors at 3/4 throttle