ignition coil

[58mf65]

I keep burning up ignition coils. they get hot and crack and the fluid inside them comes out. This is a 1958 MF 65 gas engine. I notice on the coil it states to use with a primary resistance wire or external resistor. When I follow the wiring there is no resistor and the wiring looks like 14 gauge copper wire. after I replace it the tractor runs good for awhile but then starts back firing. eventually the tractor will die and I have to replace coil again. I get the coils from a massey rep and they said i need a resistor but they do not sell them. seems weird. is there a better coil i can just buy or where do i find these resistors.

 

[cmore]

Here are some

https://www.google.com/search?q=ignition+coil+ristor

http://www.bing.com/search?q=ignition%2Bcoil%2Bristor+supliers&form=MOZSBR&pc=MOZI

 

[buckshot721]

Any auto parts store can fix you up, you can get them with a built in resistor. Or hang one off the side of the coil. Or you can get a big ole yellow ACCEL Super coil.

 

[ironnut]

You definitely need to have the resistor if the tractor has a 12 volt electrical system. As stated earlier an auto parts store can sell you the resistor. You can also buy a 12 volt coil which will not require the external resistor. Most older 12 volt electrical systems used a 6 volt coil with the external resistor or calibrated length of wire to provide the voltage drop to 6 volts. When starting the engine, the resistor was by passed and 12 volts fed directly to the coil. This helped insure that a very hot spark was delivered during the starting phase. When the key was released from the cranking position the current to the coil was supplied through the resistor which dropped the voltage to the coil to 6 volts for normal running.

gordon

 

[Oscoda]

I have a MF 135 Perkins gas 3 cylinder that seems to be overheating coils all of a sudden,the tractor runs for about 3 or 4 hours and
starts acting like vapor lock, but never runs right until I replace the coil. I am wondering if the coils from 1974 were more heavy duty
and the replacement ones are now made too light to handle the load. I noticed resistor v. non-resistor coils & plugs....is this something I
should be looking at?

 

[Jerry/MT]

Are you points looking burned too? A 12 volt coil should have ~ 3.2 ohms resistance. If you have a 6V system, the coil resistance should be ~1.6 ohms. So check the resistance with a VOM.

If you have a 12 V system and use a 6 v coil the current will double through the primary ignition circuit and will cause the points to burn and the coil to overheat. So you need to make sure that you have the right coil for the ignition system voltage. If you have a 6 V coil and you want to use it on a 12 V system, you need to put a "ballast" resistor in series with the coil to lower the current. A good 12V coil is NAPA part number IC14SB. There should be one for ^ v systems but I don't happen to know the part number.