1955 Johnson 25hp

[SumDumGuy]

I was looking at the classifieds last night and came across a "20-35hp classic johnson motor from the '50s." The ad further stated that the engine was seized. All this for $60.

Since I was looking to get a hold of a 15hp I threw the dice in hopes that it would be 20hp or lower.

I was a bit disappointed because the motor I saw was substantially larger than I was hoping, and it had the ugliest/worst paint job I have seen lately. I explained to the guy I was a bit disappointed and he stated that if I gave him $40 it was mine.

So, my new motor (new to me) turns out to be a RDE-17. It actually is not seized, but the start "thing" on the rope pull assy was engaged and thus the rope could not turn the flywheel. Anyway, as you probably can guess I have a couple of questions.

If I was to remove the electric start stuff what type of weight would come out of the motor?

AS can be seen in one of the following pics, the shift selector has been broken off. How much of a hassle will it be to locate and change this item?

 

[HighTrim]

Re: 1955 Johnson 25hp

Well you have a bit of a Frankenrude there! lol

Removing the electric start will not gain you much. Not enough to worry about. Additionally, have you ever tried pulling over a Big Twin>? The electric start is a nice option!

Test compression step 1. Let us know what you find. Jump the electric starter for this. Ground the plug leads and remove the plugs.

The shift handle is not hard to come by. If you cannot find one locally PM me.

 

[F_R]

Re: 1955 Johnson 25hp

You need more than the shift handle, you need the shaft that it attaches to. Powerhead removal is necessary to replace it. Don't throw that starter away, somebody wants it if you don't. And the starter mounting brackets are hard to come by.

 

[SumDumGuy]

Re: 1955 Johnson 25hp

Thanks for the info guys!

When I get some time I'll clean it up a bit and take a look at the starter. We'll see if I can figure out how to hook directly to it to get a good compression check.

I went ahead and tried to manually pull... yes, the starter does seem like a nice item.

 

[HighTrim]

Re: 1955 Johnson 25hp

Just screw in compression gauge into a cylinder.

Run leads with alligator clips from plug leads to ground.

Get booster cables and battery. Hook RED lead to starter post, the other end of the RED lead to the POS post of battery. Black lead from cables to starter ground mounting bracket. Now tap the other end of the BLACK lead to the NEG post of battery to get it to crank. Let it crank over a few seconds then note compression reading.

Repeat with other cylinder.

Im sure that motor will need a full tune up. If compression is good, pop the flywheel off and inpect the ignition to start.

 

[SumDumGuy]

Re: 1955 Johnson 25hp

Well, it's gotten dark now so I am at a loss to see any wire colors easily. I did get a chance to pull the manual start off the flywheel. It looks like at some point someone replaced the coils and etc. So, I guess that's good (save a couple bucks).

Oh yea, I was going to ask.... I thought I had read that the electrical for this motor is a 6v system. Is that correct? If so I should find a 6v battery for the starter? Hopefully I am just confused.

 

[Tom Maslar]

Re: 1955 Johnson 25hp

the starter is heavy, you will lose a good amount of weight--it is filled with copper so scrap it! You have a pretty rough looking old gal there. You can get the handle on e-bay or contact the aomca and get a membership. The guys in the antique outboard motor club of america can help you find that motor looking brand new if you are willing to do the research and labor--good luck!

 

[HighTrim]

Re: 1955 Johnson 25hp

Sorry still going to have to disagree. Removing the starter will not get you any speed performance that you will notice, unless you are spiderman!

Also, PLEASE do not scrap it. That is not the message we want out there. The parts are getting harder to find, and sending them to the melters does not improve that situation. Im sure a local member will pay you what the melters would.

Also the 6 volt starter can handle a 12volt battery. Don't crank endlessly on it though. The choke solenoid will fry though, that will have to be changed to a 12 volt solenoid. Another option is to put in a resistor.

 

[HighTrim]

Re: 1955 Johnson 25hp

Here are some wiring diagrams.

 

[kfa4303]

Re: 1955 Johnson 25hp

Here are some handy links.

Reviving a Vintage Big Twin - Part 1
Vintage Evinrude Johnson Outboard Parts & Diagrams - Catalog 376368

 

[SumDumGuy]

Re: 1955 Johnson 25hp

HT thanks for the diagram.
kfa appreciate the links, I hope I don't have to get too terribly acquainted with the parts diagram out of necessity.

I got some good news and what appears to be bad news this morning.

The good is the starter works great. Engages and spins everything without issue. The wiring to the motor is a wreck, however. With the motor disconnected I can get continuity to both wires (short somewhere).
The bad news is I only measured 75 psi on each of the cylinders. I will assume that is rather low. However, I am not too sure about the accuracy of the gauge. It is a harbor freight special, and we all know that HF is hit and miss. I am going to see if I can find another gauge around here somewhere and/or find a known reference to verify the gauge I have.

If it turns out that the gauge is correct I will have officially gotten out of my area of knowledge. A guess would be a possible candidate for problem would be the piston rings?
Whatever it is I guess it's no big deal. I always wanted to see what was inside one of them there engine things.

******

So, I started searching for pressures and testing for outboards and ran across a link that states:
"Good working outboards generally have a compression of 75 to 85 psi. Any readings below 70 psi are considered to be low compression."

Outboard Compression Testing

Is this true?

 

[HighTrim]

Re: 1955 Johnson 25hp

As you stated, not all gauges read the same. Try another gauge first.

Additionally, every motor is different. A Big Twin will NOT have the same compression as a CD or TN. You cannot lump them all together. While 75psi would be indicative of a low hours, healthy 5hp TN, it is low for a Big Twin powerhead. I have a few dozen right now, and have had a lot over the years. They are normally in the 100 to 140 psi range. Some guys say that as long as they are even they are ok, which is generally fine advice, I don't always agree with it myself. If testing with a known good gauge, a Big Twin powerhead should be even and over 100 psi in my humble opinion. Otherwise, I pass on them.

Now even if it is low, it is not always due to being worn out. May simply be a worn head gasket, or carboned up rings. A new gasket, dressing the head, and decarbing the motor has revived many for me. Not going to know without further inspection.

 

[SumDumGuy]

Re: 1955 Johnson 25hp

Good info, thanks. I am still in the process of locating a confirmation compression gauge so we'll see what that says.

Is there a way to tell a head gasket is obviously no good, oil "streaks" or something similar? Shipping on those gaskets is a bit much imho.

If I can get this thing to go bang I am thinking of hitting it straight out with the decarb. Does this sound like a worth while endeavor, or should i just drop the cheap-charlie thinking and buy some parts?

Thanks!

 

[HighTrim]

Re: 1955 Johnson 25hp

If you can get her to run, by all means decarb her first and see what happens. Motor may be fine as well, wouldn't worry yet. The fact that they are even is a good sign!

You just need to know where to order from for parts. If you need a head gasket, PM me in the future.

 

[SumDumGuy]

Re: 1955 Johnson 25hp

Sounds good; thanks Chris.

When I get something happening I'll let ya'll know.

 

[tjandrews]

Re: 1955 Johnson 25hp

Don't forget the lower unit! Make sure it has gear oil in there before even trying to start it. Doesn't take but a minute to tear dry gears and bearings up. And I learned from painful experience that it would be a good idea to change the water pump impeller soon after you get it to start, and before you put it on a boat.

 

[SumDumGuy]

Re: 1955 Johnson 25hp

Lower unit... haha... I forgot. Thanks for the reminder.

I did get some time to mess with this today. I started to remove the cowling, etc while I waited for the lower to drain. I did run into something strange with the lower unit oil drain/fill. I am guessing that it is a repair? The parts drawings indicate the same p/n for top and bottom.
What is the easiest way to add oil through the top, oil can?

 

[tjandrews]

Re: 1955 Johnson 25hp

Lower unit... haha... I forgot. Thanks for the reminder.

I did get some time to mess with this today. I started to remove the cowling, etc while I waited for the lower to drain. I did run into something strange with the lower unit oil drain/fill. I am guessing that it is a repair? The parts drawings indicate the same p/n for top and bottom.
What is the easiest way to add oil through the top, oil can?

Uh-oh. Your "lower bolt" is not the drain plug. It is the pivot pin for the fork that moves the clutch dog to engage either forward or reverse gears. You do NOT remove it unless you're disassembling the gear case. If you're lucky, and haven't moved anything, you may be able to replace it. Otherwise, you may have to disassemble the gearcase to get the fork lined up with the pin.

Your "upper bolt" is probably the drain plug. You'll find the other one, the vent plug, higher up, near the cavitation plate. You'll need to remove it too to drain the oil properly. You don't fill from the top - that results in air pockets. (Always use new gaskets/washers on the drain and vent plugs) You fill from the bottom until oil runs out the top, replace the vent plug while keeping the nozzle or tube you used to fill in place, then quickly remove the nozzle and replace the drain plug. You'll probably make a mess the first couple of times you do it, but you'll catch on.

 

[SumDumGuy]

Re: 1955 Johnson 25hp

Too funny, I guess that explains the reason for the "bolt" being different. It would also explain why the motor is in gear since I drained the oil (prior it was in neutral). Of course you know I had to turn everything to make sure I got as much of the oil out as possible. :lol:
I just came back inside. I was laying on the ground in the dark frantically searching the gear box for the lower drain - found it.

At this point I can only laugh at myself and realize how much more familiar I will be with this motor. :facepalm:

I'll keep updating as it goes.

Thanks!

 

[SumDumGuy]

Re: 1955 Johnson 25hp

Pulled the lower today. Not a lot of excitement, dropped out fairly easy.

Took the gear box apart as well. I think I could have gotten the pivot pin (aka "lower drain plug" :embarassed back in place without opening it, but I wanted to see inside anyway.
Everything inside looked good. From my inexperienced point of view the gears are in good shape and everything seemed to be ok - no rust or metal shavings, etc.

I s'pose I might as well leave the lower off since I will need to remove the power head to change the gear shift shaft.

Until next time....