How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

[Clippership821]

Is there a way for me to test my magneto for high voltage leakage? I've been going through a lot of rotors lately and it's been suggested that it's due to excess voltage burning a hole through the plastic base of the rotor and shorting out on the distributor shaft. Thanks in advance for your responses.

 

[tx1961whaler]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

Is it the original OEM coil? Is the correct resistor wire (red/white) used to connect to the coil? Really, the output of the coil is something like 25 kV and is impractical to test. If the resistor wire, coil, and condenser are all OK, then there should be no issue with the output voltage. I can imagine that you are pretty annoyed at going through $50 rotors, so maybe there is some type of insulating grease that can be used on the dist. shaft to help with this?

 

[Clippership821]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

Is it the original OEM coil? Is the correct resistor wire (red/white) used to connect to the coil? Really, the output of the coil is something like 25 kV and is impractical to test. If the resistor wire, coil, and condenser are all OK, then there should be no issue with the output voltage. I can imagine that you are pretty annoyed at going through $50 rotors, so maybe there is some type of insulating grease that can be used on the dist. shaft to help with this?

Thanks. Yeah, everything is connected properly. The original brush went out on it. Like, literally broke in half and split in two. Curious about that. So, I have a replacement. The rotors come greased but maybe I should try putting more on.

 

[Daviet]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

Is the resistor wire in place, what is the voltage on the wire at the coil?

 

[Clippership821]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

I'm sure the resistor wire is in place. Couldn't tell you what the what the voltage is on the wire. Do you mean while it's running or just spinning it?

 

[Chris1956]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

Clipper, you have a magneto right? If so there is no resistor wire.

I am still not clear on how voltage can be "burning" it's way thru the plastic of the rotor. Do you see any hole? Electricity will follow the path of least resistance. The lowest resistance is supposed to be to jump the airgap to the dist cap contact. You might check this gap out to see how wide it is. I have had a rotor crack and allow a carbon track to form between the rotor conductor and the dist shaft. That happened when the motor overheated. In those days (early 90's) a rotor was $7. BTW - the spark was intermittant.

 

[Clippership821]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

Thanks Chris, yes magneto on a V4SL-13 I don't see a hole or a crack. The only thing I see on the old rotor is, like you said, carbon build up on the metal piece itself. It'd be a heck of lot of voltage and spark to get through spring brush and rotor, at least you'd think so.

 

[Clippership821]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

Also, it is the original cap. Not sure what the tolerances are for that. But, it does have some wear that is noticable...I'vehad to polish the contacts up a few times

 

[tx1961whaler]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

A 1961 V4SL-13 has a battery, breaker and coil automotive type ignition with a distributor. Like an old Fiat. The magneto ignition came in 1963.

 

[Chris1956]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

Gee TX, My '59 Johnny 50HPV4 had a magneto.

I 1960 and newer V4 engines had an assortment of both magneto and battery/coil ignitions. The magneto had had the wires going straight down, right? Battery/coil has the wires coming out he side of the cap, right?
Clipper, what have you got?

 

[petryshyn]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

Check the plug wires with an ohm meter. Look for open circuit and/or heavy corrosion. An open plug wire will cause arcing through the rotor to shaft.

 

[boobie]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

Magnetos came in in 1958 with the first " Fat Four " 50 hp.

 

[Clippership821]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

I've got a magneto set up.. wires straight down. I pull the cord if the battery's dead and she fires right up.

 

[tx1961whaler]

Re: How do you test for excess voltage on 1961 Johnson Seahorse 75hp magneto?

I've got a magneto set up.. wires straight down. I pull the cord if the battery's dead and she fires right up.

Holy crap, I was looking at the wrong manual. Strangely the 1961 75 hp had EITHER battery ignition or magneto ignition, depending on the model. A V4AL-13 has the battery ignition, while the V4SL-13 has a magneto.