Merc info needed

[stanley]

A friend is looking for a motor and found this one close by.He says it’s 20hp and wants me to take a look,but I told him I know nothing about Mercury outboards but know where to find people who do,Soooo….,is it big enough to push a 15ft aluminum semi v runabout he is re-storing?what are issues peculiar to this model?are controls and tank hard to come by?are ignition parts and impeller hard to find?

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Attachments:

[outboard315]

It’s a Mark 25 and its already set up for remote steering. A couple of special tools are needed but nothing too bad. All of the replacement parts you listed are available from old mercs or a couple of other sites.

[outboard315]

Also just about any standard gas tank can be used with the mercury connector.

[billw]

They are great running motors when right. Original controls are a bit hard to find but I’m pretty sure newer Merc controls will adapt, depending on what throw configuration they are. They disappear like Alka Seltzer when put in salt water. Poof. Gear cases/gears can be a problem. Don’t even think about using it in salt water or you will go straight to Mercury Hell. Lol.

Last I knew, OEM impeller just went NLA but you may find others. Most Mark 25s I have seen have good coils but it’s all still available aftermarket. If you ask me, it’s a little under-powered for a 15 footer but will work, especially if you pick up a three blade, lower pitch than what’s on there now.

Long live American manufacturing!

[20mercman]

The motor is a 1955 Mk-25 as has been posted. These are very popular with the Mercury folks, and were a significant upgrade from the Mk-20. These use a Phelon ignition system that is very reliable. It will most likely be in need of a rebuild on the magneto as the coils will be bad if they have not been replaced. I would also recommend the condensers be replaced at the same time. The lower crank seal may also be ready for replacement by now. (it’s 61 years old!) These are very nice running motors. Like was posted, they are fairly straight forward to work on. I have built 10 of these, and I don’t have any real special tools except a tool I made for removing the water pump cover and the gear case cover. A high quality spanner wrench will often work if they are not badly corroded in place. Lower unit seals and really anything on a motor of this age should be checked and make sure they are in serviceable condition. These will easily outrun our 1956 FD-10, but they are a bit louder. Very compact design for the 18-20hp range motors. (55 were rated at 18hp, 56 and later were 20hp, but really the same motor.)

This particular motor looks very good for being an original. I would not hesitate to add this one to my collection as it has certainly been well cared for. Any motor that you want to be reliable no matter who built it should be renewed to make them dependable. These were OK’d by Mercury to be run on 50:1 as they were "Full Jeweled Power" (Roller and needle bearings on all bearings)

Ask any questions.

Steve

[20mercman]

quote 20mercman:

The motor is a 1955 Mk-25 as has been posted. These are very popular with the Mercury folks, and were a significant upgrade from the Mk-20. These use a Phelon ignition system that is very reliable. It will most likely be in need of a rebuild on the magneto as the coils will be bad if they have not been replaced. I would also recommend the condensers be replaced at the same time. The lower crank seal may also be ready for replacement by now. (it’s 61 years old!) These are very nice running motors. Like was posted, they are fairly straight forward to work on. I have built 10 of these, and I don’t have any real special tools except a tool I made for removing the water pump cover and the gear case cover. A high quality spanner wrench will often work if they are not badly corroded in place. Lower unit seals and really anything on a motor of this age should be checked and make sure they are in serviceable condition. These will easily outrun our 1956 FD-10, but they are a bit louder. Very compact design for the 18-20hp range motors. (55 were rated at 18hp, 56 and later were 20hp, but really the same motor.)

This particular motor looks very good for being an original. I would not hesitate to add this one to my collection as it has certainly been well cared for. Any motor that you want to be reliable no matter who built it should be renewed to make them dependable. These were OK’d by Mercury to be run on 50:1 as they were “Full Jeweled Power” (Roller and needle bearings on all bearings)

Ask any questions.

Steve

Edit: I agree with Bill that pushing a larger hull, you would be much happier and so will the motor with a 3 blade 9P prop vs. the 11P that is on this motor.

[stanley]

Thanks for all the info.Great info and super fast response.Once again it shows the value of supporting this forum by becoming a member of AOMCI.

[PM T2]

Isn’t there an earlier style Dyna-Float cover that was used on the MK-25? I thought there was a plain style used for 1955. Just curious.

Best,
PM T2

He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...

[dave-bernard]

just on the early ones.

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