Reviving an old Johnson Seahorse 6

[ProDave]

I have been given an old Johnson Seahorse 6 OB motor, non working that I am trying to revive, more as a bit of fun than any intention of using it seriously.

It's a 2 stroke 2 cylinder 6HP motor. Here is the identification plate. I wonder if anyone can work out the approximate age from that? and is there any service information available on these old motors?



What I know / have tried so far:

Turns over okay, seems to have compression (effort needed to turn it with plugs in vs plugs out)
Both plugs spark.
No sign of life at all.
Plugs dry so no fuel reaching plugs.
But even if a splash a little fuel in the plug holes and try it does not even cough (a trick I do with my strimmer when being reluctant)

So obviously it needs carb off and checked out. Of course one of the 2 fixing bolts is easy and the other is inaccessible by spanner so other bits I think the starter mechanism needs to come off first (hence some service info would be handy)

Generally it looks quite clean so I suspect little use and been inactive for a long time.

And a general observation, this motor seems to operate in a completely strange way to me compared to anything I have seen before, most obvious being rotating the throttle seems to rotate a plate under the flywheel that I think holds the magneto ignition, But surely rotating it is changing the ignition timing depending on throttle opening.

 

[wallacebob]

Look here for year and model data. https://www.marineengine.com/manual...sE0mMnOucjk9vMDqfnhgHmQUtZA1FhUwbpdMS3hajmKDd

I had a couple of 5hp. Great engines, but very fussy about fresh fuel and clean plugs. Always use premium petrol plus stabiliser.

 

[neil_s]

Be careful - renovating old outboards can be addictive - I've got four hanging up in the shed!

 

[ProDave]

Look here for year and model data. https://www.marineengine.com/manual...sE0mMnOucjk9vMDqfnhgHmQUtZA1FhUwbpdMS3hajmKDd

I had a couple of 5hp. Great engines, but very fussy about fresh fuel and clean plugs. Always use premium petrol plus stabiliser.

Thanks. That dates my engine as 1968, so 57 years old.

 

[LittleSister]

Reviving an old Johnson Seahorse 6​

Try feeding it Studland Bay seagrass!

 

[Refueler]

I have 2 Johnsons 3hp and 5hp ... 2 Mariners 2hp and 20hp .... 1 Evinrude 18hp ..... all 2 strokers on 50:1.

I have NEVER had the need for Premium fuel - straight 95 has been good enough .. and for some time here - 95 has been E10 ...

I have no use for stabiliser ..... old fuel gets mixed with new ....

I may have an engine reluctant to start at times - that's down to how I stopped the engine last use ... I usually turn of the fuel and let carb run out to stop engine if its going to be longer than a day.

 

[Snowgoose-1]

Be careful - renovating old outboards can be addictive - I've got four hanging up in

Yes, outboards can be addictive. I have a 4hp twin Seahorse which is surprisingly powerful. Also an Evinrude which is quite similar. Both having a touch of the smokey Robinsons though.

 

[William_H]

I had a Johnson 6HP for 40 + years. (about 1082 model) Great engine I have just given it to scrap metal man for 2squid. It always started easily but I did replace the capacitive ignition unit at one stage. It uses a coil under flywheel to provide a high voltage to a capacitor which is discharged via silicon control rectifier into a coil to provide a spark. Works well.
Yes on advance of the throttle the timing is also advanced by rotating the coil mount plate.
My problems were mostly in the cooling system. Not so much the impeller but the channels under the power head. The copper pipe runs up the exhaust tube with cooling water. This runs through a gallery then through power head to thermostat. Some models seem to vary here. It was quite a job to separate leg from power head.
The trick is to remove the gear box and pump and put a garden hose on to the end of the copper pipe. Should get water out of tell tale and also coming down the exhaust tube. (leg)
Another problem was corrosion making gear shift tight. Yes there is a grease nipple but shaft had to be pulled out to free it. I made an extension to the gear lever so i could reach it. Also pressed a piece of rubber hose over the throttle handle to make it easier to reach on o/b bracket on my trailer sailer.
In the end I did not use it because it was so heavy. OK when I was younger. Bought a Honda 2.3 no water cooling and much lighter. ol'will

 

[VicS]

Thanks. That dates my engine as 1968, so 57 years old.

Two tests to do before you start tearing into things.

1. A compression test. If not 80psi or better its probably not worth bothering with.

2. Spark strength using an adjustable gap spark tester. If spark is poor suspect the coil or condenser.

A 1968 model has coil and points ignition, not the CDI system that William describes. Numerous other differences too. I have a 1984 Evinrude which is more or less the same as William's Johnson.

If you get it running you will need to replace the water pump impeller before you use it. Look at the parts diagram on the MarineEngine site and note the collection of components at the top of the drive shaft and the roll pin that supports them. IIRC the pin has to be aligned ( trial and error) with a slot before the shaft can be withdrawn. The shift rod is in two parts which must be disconnected and when reassembled the two parts must be fully inserted into the clamp or the gear shift will not work properly.

DO NOT remove the small screw opposite the gear case drain screw or the gubbins inside will all fall out of position.

 

[Snowgoose-1]

I have been given an old Johnson Seahorse 6 OB motor, non working that I am trying to revive, more as a bit of fun than any intention of using it seriously.

It's a 2 stroke 2 cylinder 6HP motor. Here is the identification plate. I wonder if anyone can work out the approximate age from that? and is there any service information available on these old motors?

View attachment 197754

What I know / have tried so far:

Turns over okay, seems to have compression (effort needed to turn it with plugs in vs plugs out)
Both plugs spark.
No sign of life at all.
Plugs dry so no fuel reaching plugs.
But even if a splash a little fuel in the plug holes and try it does not even cough (a trick I do with my strimmer when being reluctant)

So obviously it needs carb off and checked out. Of course one of the 2 fixing bolts is easy and the other is inaccessible by spanner so other bits I think the starter mechanism needs to come off first (hence some service info would be handy)

Generally it looks quite clean so I suspect little use and been inactive for a long time.

And a general observation, this motor seems to operate in a completely strange way to me compared to anything I have seen before, most obvious being rotating the throttle seems to rotate a plate under the flywheel that I think holds the magneto ignition, But surely rotating it is changing the ignition timing depending on throttle opening.

I do not know if the 6hp is like the 4hp, but it spits much less water from the pee hole than most other outboards. Apparently this is normal . Perhaps others can confirm if it applies to the 6hp model.

 

[VicS]

I do not know if the 6hp is like the 4hp, but it spits much less water from the pee hole than most other outboards. Apparently this is normal . Perhaps others can confirm if it applies to the 6hp model.

The older ones do not have a separate cooling water telltale like later ones ( eg my '84 model) and most other modern outboards, but like the 4hp you get some water blown from the back pressure relief port on the exhaust housing. I think probably more than from a more recent 4hp

 

[Snowgoose-1]

The older ones do not have a separate cooling water telltale like later ones ( eg my '84 model) and most other modern outboards, but like the 4hp you get some water blown from the back pressure relief port on the exhaust housing. I think probably more than from a more recent 4hp

Thanks Vic.
Nice explanation.

 

[ProDave]

Right, I think I have the problem, or at least the first problem.

Although I was seeing a spark, it was very weak, so much so I had to get an assistant to look at the plug while I pulled the starter. As suggested above I got my spark tester out and could not even see a spark on that.

So flywheel off and this is what I see.



It doesn't take a genius to work out those magneto coils are seriously unwell.

The condensers look new, I suspect the previous owner replaced them to try that.

So unless I can find a pair of replacement magneto coils for not much money I think it ends here.

 

[Blueboatman]

What happens when you wire a car coil and battery through the existing points?

I have done this with a fubar magneto and enjoyed years of reliable motoring afterward

Edit
I would be primarily interested in the backlash of the mechanicals at the powerhead and the compression available .
Fun project though

 

[ProDave]

What happens when you wire a car coil and battery through the existing points?

I have done this with a fubar magneto and enjoyed years of reliable motoring afterward

Edit
I would be primarily interested in the backlash of the mechanicals at the powerhead and the compression available .
Fun project though

Interesting idea. To do it properly would need 2 car coils. But if I parallel the 2 points into one car coil and feed 2 plugs from it, it would not matter they are both sparking twice as often as needed.

 

[Blueboatman]

Interesting idea. To do it properly would need 2 car coils. But if I parallel the 2 points into one car coil and feed 2 plugs from it, it would not matter they are both sparking twice as often as needed.

Iirc you understand sparks better than I so thought it might be worth a play

I think the wasted double spark was not uncommon from new on some set ups

 

[ProDave]

My idea won't work. The points open when the spark is needed, so parallelling them it would never spark.

Plenty of replacement magneto coils available. Most are about £20 each. But I have found one on ebay clearly saying £20 for a pair. However although it looks the same and the seller says they fit the 6HP engines from 1950 to 1976 it has a different part number.

The parts list linked above says mine should be 0580416 but the ones being offered say equivalent to part nos
584477 582995 582921

 

[Refueler]

Seriously .... if you can get the parts - FIX IT ....

2str 2nd hand market is healthy ... not everyone wants a 4str ... so even if you were to put it on eBay or whatever - I'm sure there would be a buyer ..

 

[Hot Property]

Be careful - renovating old outboards can be addictive - I've got four hanging up in the shed!

Hmm, somewhat light I fear...

My Current crop awaiting disposal:-

Tohatsu 3.5 2 stroke
Tohatsu 3.5 2 stroke
Mariner 2 2 stroke
Mariner 3.5 4 stroke
Mariner 25 2 stroke
Suzuki 15 4 stroke
Mariner 15 EFI

The purchases all seemed a good idea at the time!

Don't let my wife sell them for what I told her I paid for them please....

 

[Blueboatman]

My idea won't work. The points open when the spark is needed, so parallelling them it would never spark.

Plenty of replacement magneto coils available. Most are about £20 each. But I have found one on ebay clearly saying £20 for a pair. However although it looks the same and the seller says they fit the 6HP engines from 1950 to 1976 it has a different part number.

The parts list linked above says mine should be 0580416 but the ones being offered say equivalent to part nos
584477 582995 582921

I missed that completely , duh!