(Chrysler 25 HP 1975) Outboard Motor 257HA

[ic2droids]

So we are restoring our family boat with motor and trying to bring it back to life. The question I have it’s using the Mercury-Mercruiser 85-818076A2 coil I found online it should have a 9,400-11,700 Ohms. One is cracked and the other seems to be okay. I looked online and they are $120-180 each. What test can I do to make sure the other one is good and for the broken one can I install another type of coil? I know it’s 12v it says it on the side. But I don’t know if it’s got an internal resistor or if I can use one of the generic ones from Amazon?

 

[ErSa]

I used these ones on my 55 hp Chrysler. Thriumph motorcycle coil.

 

[ErSa]

Forgot picture of motorhead.

 

[topgun3690]

Member "Nordin" may be able to answer questions about using automotive or alternate ignition parts on these motors.....you might PM him and ask.....

 

[Nordin]

ErSa has one solution, coils from motorbikes.
It has to be 12V coils for battery ignition systems.
Another solution is to use regular auto style coils but not with ballast resistor.
Auto style coils can be a bit tricky to assemble cause they are larger then the OEM and coils for bikes. Especially on the 25Hp cause there is less space under the cowl then the lager engines (35, 45 and 55Hp).
If you try auto style coils, do not use coils with oil insulation.
It has to be dry (without oil) coils.

 

[jerryjerry05]

Spark tester: then if you get spark clean and seal the old ones.
That plastic dip,spray work well.
I use shrink tube and liquid electric tape for the wires and buy new cable ends

 

[ic2droids]

Okay I’ll probably get a motorcycle one. Now should it have the resister inside or no? If I spark test one with and without the resister it should still spark right?

I like the idea to cover it in heat shrink then plastydip, or liquid electric tape to seal it that’s great!

 

[ic2droids]

Maybe this one will work? https://a.co/d/2cCHHeu

 

[ic2droids]

I’ll check the ohms of the good coil. One is cracked and is bad I know that. I see some are 1.5 and others are 3 ohms. Need to find that out before I buy one

 

[ic2droids]

So both tested at around 3.5 ohms on the pins and around 8.9 ohms from center to pin. The other “bad one” shows nothing on the ohm test so it’s bad.

 

[ic2droids]

How would I check the voltage? They say 12v on them. If they are 12v would that mean they have a resistor in them or don’t have one at all?

 

[Nordin]

I am not sure about built in resistors as they I have worked with has the resistor outside.
Do not use coils with resistors, it is for cold start a car.
OB do not need this.
If the coils is for 12V... fine, you can use it.
If there is a crack in the coil, well try to insulate it with some kind of putty and shrink tubes and try.
BUT there can be bad insulation inside the coil between the prime and secondary side of the coil, then the coil is shot.

 

[ic2droids]

They didn’t have any resistors on the outside of them. (I think some of the 12vs had inside resistors to make them 6v) So maybe a 3 ohm 12v motorcycle one would work. I’ll order some and check with a spark gap tester to see if they have spark.

 

[Nordin]

Prime side of all ignition coils would read about 0,5-3 Ohm.
Secondary side is more different. Coils for CDI ignition would read about 200-800 Ohm depending on brand and system, magneto coils would read about 5-8KOhm and battery ignition 9-15KOhm.

 

[ic2droids]

Here’s some pictures of them. One the secondary side, spark plug wire side doesn’t ohm out on one so that is bad. Other one seems to be good and ohms out at 8.97 and both prime sides ohm out at 3.4 and 3.5 ohms

 

[ic2droids]

So been a wile, having a kid takes up a lot of your time. So ready to start working on this boat again. Cant seem to find non oil filled 12v motorcycle coils. As you can see in the images they are both around 3.4 to 3.5 ohms and almost 9ohms on the spark side. The cracked one has 0 ohms on spark side so its internally damaged so cant fix that one. will an oil fill 12v motorcycle work without issues and do I have to use the can style or can I go with something smaller with same ohm, 12v, and 2 wire?

 

[Nordin]

Non oil coil is to prefer but if you can not get one use one with oil.
All 12V ignition coils built to use in battery system will work.
Prime side winding 0.5-3.5 Ohms, secondary side about 9-11 kOhms.