1958 Johnson 7.5 Seahorse

I recently purchased a 1958 Johnson Seahorse 7.5 for $125 and am pretty excited about getting it into good working order. This is my first time working on an outboard. I have two questions to start with:

First how do I replace the spark plug wires? I took the flywheel off and am replacing both coils/points/condensers since I have the flywheel off. I purchased spark plug wire by the foot and two springs. I haven't received them yet so I might be able to figure it out once I get the parts, but I was just curious about how that works.

How do I replace the impeller? I was able to get to it by removing the clamp, and the engine from the top to take the shift rod loose. I was going to have to do that anyway because I had to replace the shift lever.

I really appreciate any help.

mengo45 said:

1958 Johnson Seahorse 7.5.... I have two questions to start with:

1 - First how do I replace the spark plug wires?

2 - Second How do I replace the impeller?

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1 - Remove the armature plate (plate the points are attached to).

2 - Dismantle the water pump. On top of lower unit, front portion....thing the driveshaft goes through.

(Replacing Regular Spark Plug Wires)
(J. Reeves)


If you also need the spark plug boots and the spring terminals that connect to the spark plugs, purchase them from your local dealership (OMC Part #581027). This includes one boot and one spring connector. Price is about $3.25ea.


Purchase whatever amount of spark plug wire you need. Be sure to purchase the kind that has a steel (or copper) twisted wire leading through the center of it....... not the carbon type plug wire that many automobiles now use.


Using your old plug wire, cut the new wire to a length about 3/4" to 1" longer. If you have no old plug wire, just make sure that the wire is longer than you'll need as you can trim the other end later.


The rubber boot, spark plug end.... With the wire cut to the length required, trim back 1/4" insulation again but do not solder tint the wires. Simply fan out the wires and fold them back against the insulation, cutting the excess off as explained above. Holding the spring wire terminal, estimate where the prong should be inserted so that the spring will be flush against the exposed wire. Hold the spring terminal away from the wires end (sideways) and insert the prong into the insulation and into the center wire, then swing the spring terminal in front of the exposed wire portion (makes a tight fit for continuity purposes). Spraying the inner portion of the boot where the wire will insert with a small amount of WD40 makes the installation of the wire a easy project.


Now, the other end that slides into the magneto coil... Look into the awaiting hole of the coil and you will see a somewhat threaded tapered prong. Double check to make sure that the wire is cut to the length required (better slightly longer than shorter), trim back 1/4" insulation again but do not solder tint the wires. Simply fan out the wires and fold them back against the insulation, cutting the excess off as explained above, then simply slide the wire into the coil so that the inner wire core of the wire is impaled by the tapered prong within the coil. That's it.... you're done.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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(Magneto & Driver Coil Alignment)
(J. Reeves)

To align the coils properly, have the metal vertical portion of the coil yokes aligned with the inside edge of the bevel that exists on the top portion of the aluminum seat upon which the coils sit. This creates the proper distance between the coils and the flywheel magnets. Faulty alignment creates friction and the yokes of the coils heat up, turn blue and expand.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:
http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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(Point Setting Of Magneto Models)
(J. Reeves)

Set the points as follows. Have the flywheel key aligned with the fiber rubbing portion of the ignition points. Adjust the gap so that a .020 gauge will pass thru but a .022 will not. Should there be any question of the points being dirty (touching the contact with your finger would cause them to be dirty), clean them with a small brush and acetone or lacquer thinner.

NOTE 1: Should the operating cam have a small portion on it with the word "SET" imprinted, align this portion with the fiber rubbing portion instead of the flywheel key.

NOTE 2: Should the cam have the word TOP embossed on the top of it, that is a cam that could be installed upside down and this is simply telling you which side is up. It is not a position where one would set the points.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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Thank you for the details that was very helpful. I will let you know if there is anything else I need. Is there a place to get new decals if I end up painting everything?

mengo45 said:

Thank you for the details that was very helpful. I will let you know if there is anything else I need. Is there a place to get new decals if I end up painting everything?

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I doubt that very much but you might try one of the antique outboard forums... I don't remember their site address.

Decals are readily available-----Try ----nymarine----Note prices may be in Canadian $------------------But I always say get it running properly first before spending hard earned coins on cosmetics.

What gas/oil ratio are you using? 2 hose tank included with purchase?

racerone said:

Decals are readily available-----Try ----nymarine----Note prices may be in Canadian $------------------But I always say get it running properly first before spending hard earned coins on cosmetics.

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I was planning on making sure it was running solid first. Thought maybe I would save the paint and pretty as a wintertime project if I can get it running now. Although from what I have read these motors are good to just use no need to make them showroom ready if I am just using it for fishing.

What gas/oil ratio are you using? Two hose tank included in purchase?

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I was planning on using 24:1 ratio, but I am wide open for suggestions as what is best. Yes I was lucky enough to get a tank and hose with ends for the $125. I ordered a new length of hose. I also tried the push button on the tank and it seemed to work. I didn't order any parts for the tank yet though.

The ratio of 24/1... 1 qt of good quality 50/1 oil to 6 gallons of gasoline is the mixture to use on that engine. 87 octane gas will be fine.

Did the coils come with new boots? You must screw the wire into the coil and then slide the boot on tight and then install the coil. The top plug wire has a band of it be sure and transfer the band so you dont accidentally put the plug wires on backwards. Take pics of both sides of the plate so you get the right wire going to the right coil. It is time consuming but once you get it running with the points set at .020 put a timing light on it and check the timing There are two marks on the points plate and a single mark on the flywheel one for each set of points. Ignition timing is on point gap you want the single mark to be inbetween the two marks on the plate.