1955 cd-12 seahorse

[white95v6]

hey this is my first post on these forums. and i have been reading for awhile.

i got a few questions on this old engine we bought. it runs and seems to run good.

1st question what kinda rpm should this engine turn. it seems to be turning less rpm then i would have guessed it to turn. i think it may be turning like 3k or soo.

2nd how fast do you guys think this engine would push a 14ft MonArk flat bottom John boat. right now i am thinking its going about 7-8mph max with about 450-500lbs in the boat. we sure would like to go about 12-14mph if possible.

3rd i looked around about some info on different props for this engine. not sure if we even need one since it seems like the engine is not making much rpm. just thought i would ask.

 

[OptsyEagle]

Re: 1955 cd-12 seahorse

1) The original spec was for 3500-4500 RPM at WOT.

http://www.old-omc.de/j_1955/seite_08to15.jpg

2) 7-8 mph is about what my 1961 5.5Hp Johnson pushes my 14 foot boat. To double that, I would suggest a 9.9Hp motor or a much smaller boat.

3) I don't know how many variations of props there are for that motor. Depending on what you are using the boat for a different prop might help, but at the end of the day, it is a 5.5Hp motor. Great for one guy who wants to troll all day, but not really a touring motor, if you know what I mean.

 

[F_R]

Re: 1955 cd-12 seahorse

hey this is my first post on these forums. and i have been reading for awhile.

i got a few questions on this old engine we bought. it runs and seems to run good.

1st question what kinda rpm should this engine turn. it seems to be turning less rpm then i would have guessed it to turn. i think it may be turning like 3k or soo.

2nd how fast do you guys think this engine would push a 14ft MonArk flat bottom John boat. right now i am thinking its going about 7-8mph max with about 450-500lbs in the boat. we sure would like to go about 12-14mph if possible.

3rd i looked around about some info on different props for this engine. not sure if we even need one since it seems like the engine is not making much rpm. just thought i would ask.

So, you really are only guessing at speed? "Real" speed on that boat with 500 pounds in it is going to be 9mph or less. You Might get it up to 11 or 12 with a minumum load, assuming you can get it up on more or less of a plane. Best speedometer for a small boat? A hand held GPS. But most people are only disappointed if they know their true speed.

 

[white95v6]

Re: 1955 cd-12 seahorse

yea i forgot my buddies gps that day. so 7-8mph is my guess.

hmm i would have thought it would have turned more rpm then that. but if thats what oem says then good. it seems to sound close.


oh and i seen on a post on here to use a 26:1 mixture for this old engine with the newer oils. does this sound right. cause we have oil dripping outa the exhaust after a few runs on the lake.

 

[Huron Angler]

Re: 1955 cd-12 seahorse

My 5.5hp '55 Johnson pushes my 12' semi-V hull about 8mph with two guys. As mentioned, it will never really plane and is best for trolling.

When my two boys are 10-12 years old they will be able to plane it out and have some fun though

My understanding is 24:1 ratio of gas/oil for these OMC OBs.

 

[white95v6]

Re: 1955 cd-12 seahorse

My understanding is 24:1 ratio of gas/oil for these OMC OBs.

yea sorry i went back and read some more posts and it seems 24:1 is what everyone is saying. and thats what we ran it at 1 quart oil to 6 gallons gas.

hmm might go through the carb. just seems to be running real rich even with the mixture screw on lean.

thanks alot guys.

 

[1946Zephyr]

Re: 1955 cd-12 seahorse

24:1 is kinda thin on that motor. 16:1 is actually better (8 ounces per gallon). But that's just my opinion. 24:1 is actually the mix called out on the bigger non-friction type motors with the needle bearing crank and rod sets. The 5.5's and 7.5's in these years are all friction type motors, as were the JW's/Lightwins. 5.5's, 61 and later were needle bearing motors and were set up for 24:1.

 

[white95v6]

Re: 1955 cd-12 seahorse

man i could not imagine anymore oil in this thing. like i said we may just need to work on the carb some.

i mean after we run it.and drive home. we will have a wet oil spot where ever we park the boat at.