1955 Johnson CD-12 Engine Knock

Joined
Oct 13, 2012
Messages
29
I have been using a 1955 Johnson CD-12 all summer with no issues.

Had it out the other day and after about 5 minutes it started bogging down, and before losing all power, it developed a nasty knock.

I brought it home, and re-started the motor in a barrel of water. It started on the first pull but is running very rough, under powered and still has an awful knock to it.

The coolant water output flow is a strong as it has been all summer, so it is getting water.

One important fact: I may have been running 50:1 in it. I filled up at a dockside pre-mix pump. A fella who was camped beside me said he used that same fuel in his old outboard all the time with no issues. I am afraid that may be my problem. Before I restarted it, I mixed up a batch of 16:1 but that obviously did not help as the damage must already be done.

The question here is, did I ruin my motor? I am not a mechanic, so tearing down and rebuilding this motor will certainly be a challenge for me and I am not sure if the parts would be readily or affordable available.

I was hoping it was something as simple as a fouled plug, but although the plugs do seem a bit gritty and oily (no metal pieces, only carbon) they do not seem like they are bad. Would a non-firing plug make a knock?

The wife is going to have a fit if I tell her I blew the motor on the boat. She was against the purchase to begin with so if I can get out of this with my shirt still on my back it will be a miracle!

Thanks in advance for any advice y'all can lend me!
 
M

Maxz695

Guest
Re: 1955 Johnson CD-12 Engine Knock

This is a merc section but can I ask when you refueled did you add some oil then gas repeat or dump the oil in then fuel it. Visa versa fuel it then dump the oil in. I understand there is no mixing tank at the local gas dock.<Edit> You say a premix pump? Never seen that but often wished there was one around here. When this happens I put some oil then fuel and repeat continuosly so at least some of the oil gets mixed with the parts of gasoline added. If you fueled first more than likely close to straigh gas was pumped into the engine and lack of lubrication has done the motor in. Then contiuing on for however long you did with it knocking probably did even more damage. I,m thinking wiped crankshaft at the very least Just my opinion. Are you saying your engine reuires 16:1 using 50:1 would just be over lubing it which could foul a plug but not cause internal damage. You can try changing out the plugs but knocking is an indication of internal damge.
 

Chinewalker

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8,902
Re: 1955 Johnson CD-12 Engine Knock

Running the old babbit bearing Johnson 5.5s on 50:1 can easily turn them into scrap aluminum.

VERY good chance it has eaten a connecting rod. Do a compression check and stick a dowel into the spark plug holes to see if you have any back and forth play in one of the pistons. Also, check for any dimpling in the crankcase where it might appear something from inside has tried to get out...
 
Joined
Oct 13, 2012
Messages
29
Re: 1955 Johnson CD-12 Engine Knock

I am sorry for posting this in the wrong thread, I thought I clicked the right one. Perhaps it can be moved?

It sounds like I screwed up big time both with the motor and the post.

I will try to see if there is any play in the cylinders and if there are any bulges in the crank case.

Any hopes of this being a simple bad plug are fleeting away fast. :(
 
M

Maxz695

Guest
Re: 1955 Johnson CD-12 Engine Knock

I din,t know about the babbit bearings. Hopefully when dismantled the crank didn,t get wiped and new bearings can be instaled with a good cleaning inside the case. You may get lucky on ebay and find a good used crank for abot 100 to 200.00 bearings shouldn,t be too expensive so if you can do the work it may not be that bad considering of course nothing eles was affected. Good luck
 

RogersJetboat454

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2,964
Re: 1955 Johnson CD-12 Engine Knock

Are you saying your engine reuires 16:1 using 50:1 would just be over lubing it which could foul a plug but not cause internal damage.

A 50:1 mix would mean there is LESS oil (50 parts gasoline, to 1 part oil) than a 16:1 mix (16 parts gasoline, to 1 part oil).
These old motors are usually happy running at 16:1, 20:1, or 24:1. 50:1 is way too thin an oil mix with out the aid of modern roller bearings.

Louisville, there's a good chance shes hurt bad, but the good news is that there are a decent amount of serviceable parts in the world to fix her up. Working on these motors isn't rocket surgery either. She was built in a time when all you needed was common hand tools, and a little bit of working knowledge to fix them. If you can get your hands on a factory service manual, you are half way there. Worst case is finding a decent powerhead, and swapping your parts over (if you want to keep her). Other then that, she can also be parted out to allow the rest of her siblings to live on.
 
Joined
Oct 13, 2012
Messages
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Re: 1955 Johnson CD-12 Engine Knock

I din,t know about the babbit bearings. Hopefully when dismantled the crank didn,t get wiped and new bearings can be instaled with a good cleaning inside the case. You may get lucky on ebay and find a good used crank for abot 100 to 200.00 bearings shouldn,t be too expensive so if you can do the work it may not be that bad considering of course nothing eles was affected. Good luck

To be honest, as much as I loved this motor, at $200 for replacing a crank which is probably above my skill level anyway, I would probably have to scrap it and save for a newer 9.9. As I said, my wife will not be happy with me, as she said this boat will be nothing but a money pit, but perhaps over the winter I can soften her up.

Damn shame, and it hurts more knowing that I may be the one who created the problem to begin with by not using the proper fuel oil mixture. Ouch.
 
M

Maxz695

Guest
Re: 1955 Johnson CD-12 Engine Knock

Thats a rough est search ebay you never know what you,ll find and sometimes people will sell them for next to nothing. Even if there isn,t a make an offer I sometimes write the seller and he makes a deal with me. You wount even know if you need one until you dismantle it.
 

Chinewalker

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Re: 1955 Johnson CD-12 Engine Knock

$200??? No way. You can get complete running motors for that amount in my neighborhood. If you want to get into the powerhead, I have a crankshaft I'd let go for a LOT less than that... PM me if you're interested...

To be honest, as much as I loved this motor, at $200 for replacing a crank which is probably above my skill level anyway, I would probably have to scrap it and save for a newer 9.9. As I said, my wife will not be happy with me, as she said this boat will be nothing but a money pit, but perhaps over the winter I can soften her up.

Damn shame, and it hurts more knowing that I may be the one who created the problem to begin with by not using the proper fuel oil mixture. Ouch.
 
Joined
Oct 13, 2012
Messages
29
Re: 1955 Johnson CD-12 Engine Knock

Well I went home last night and tried the pencil eraser push test on the piston heads.

Sure enough, the lower cylinder has a very slight play to it when I push back on the head after advancing it by slowly rotating the fly wheel. I checked both and the upper cylinder was nice and secure but the bottom clearly felt like it had a few microns of play, enough to undeniably detect it through the pencil.

Thank you to all who gave me suggestions. It was enough of a diagnosis to convince me to start looking for a buyer for this motor so I can add the proceeds from the sale to future savings and buy a 9.9.

This old 5.5hp was nice for sure, but we have 7 mile long lakes in my neck of the world and with a top speed of 6 mph (wind at my back) it takes a while to navigate them all.

Thanks again for your wonderful resources!
 

dockrat100

Petty Officer 2nd Class
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Mar 22, 2011
Messages
144
Re: 1955 Johnson CD-12 Engine Knock

I just bought a complete powerhead for $100 shipped on aomci.com. If you part out the motor, that is a good place to do it. Good luck.
 

HighTrim

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Jun 21, 2007
Messages
10,486
Re: 1955 Johnson CD-12 Engine Knock

Parts are actually not as rare or expensive as you think. Ive sold many cranks for 15 or 20 bucks. Posting on the webvertize of aomci.org is a good place to start looking, forget ebay. Everything is overpriced.

Regarding the fuel/oil mixture, Im sorry about your mistake. These motors just werent designed to run on that lean a mix. I have never seen a pre mix pump before?? Didnt even know they existed! Seems like the owner would be taking on quite a liability doing that, especially if his mixture wasnt mixed very well.
 

lindy46

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Nov 27, 2008
Messages
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Re: 1955 Johnson CD-12 Engine Knock

I have a powerhead if you want to go that route. Cheap, too. Simple job to change it. Takes about 45 minutes to remove the old and bolt on a new one. PM me if interested.
 
Joined
Oct 13, 2012
Messages
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Re: 1955 Johnson CD-12 Engine Knock

Thanks to all for the suggestions and parts offers.

I am going to part out this motor and look for a 9.9 to run. I enjoyed the 5.5 as it started with one pull almost everytime, even in 32 degree temps. But it just is not enough power to take my 14ft aluminum faster than 5-6mph with the wind at my back. I fish at several lakes around here that are 7 miles or longer. I would like to be able to traverse the entire lake in less than the hour and a half it takes me now.

Not to mention that my wife was never too crazy about having such an old motor on the boat and she was always nervous about it breaking down. Granted, it broke down because of operator error, and considering ANY engine can fail at ANY time, it is not quite fair to blame the age of the motor. But when it comes to spending money on a bigger "newer" motor, the more support I get from her, the better. If it means playing along with the "old motor" routine, I am game.

I am not much of a mechanic. Typically I have a way of doing more damage trying to "fix" things. So I best leave the wrenching to those who know what they are doing.

About the pre-mix pump..We have them all over Ohio..I am quite surprised to hear others say they have never seen one. I guess I always assumed they were common?!

Thanks again guys!
 

1946Zephyr

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Oct 21, 2008
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Re: 1955 Johnson CD-12 Engine Knock

I have a powerhead if you want to go that route. Cheap, too. Simple job to change it. Takes about 45 minutes to remove the old and bolt on a new one. PM me if interested.


Is that the one I bought the cover off of?
 

RogersJetboat454

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Re: 1955 Johnson CD-12 Engine Knock

I am going to part out this motor and look for a 9.9 to run.

It's good to hear you say that... Allot of people would send her to scrap to be melted down, and turned into the next Chinese produced widget. At least this way, parts of her live on to help other motors with problems. And... you will probably make more money in parts, than you would if you scrapped her. ;)
 

orbanp

Petty Officer 1st Class
Joined
Jun 26, 2011
Messages
324
Re: 1955 Johnson CD-12 Engine Knock

...
One important fact: I may have been running 50:1 in it.
...

If anything went it is not the crank but the wrist pin in the piston. That has the journal bearing, a brass or other bearing material bushing in the connecting rod and the wrist pin. That is replaced in later motors with a needle roller bearing allowing for 50:1 gas-oil ratio.
If you can remove the wrist pin without destroying the piston, then you would just need a new bushing installed in the con rod with a new wrist pin.
I would take it apart and have a look before deciding if to junk the motor.

EDIT:
Ooops, just looked up the parts catalog of the engine. The crank bearings of the con rod are also journal bearings. So those could also be damaged. Previous statement that it just might be wrist pin damage is not probable.

Good luck, Peter
 

1946Zephyr

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Joined
Oct 21, 2008
Messages
5,556
Re: 1955 Johnson CD-12 Engine Knock

I would just pull the powerhead down and inspect the crank and rods. Who knows, you may only need to pollish the crank and replace the rod. You may have discovered the noise early enough to prevent damage. What you likely did, was heat up the rod and stretched the cap a bit. A replacement connecting rod will be a lot cheaper than buying a whole powerhead.
 
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