bolensst120

I have a Bolens ST120. I bought it, not running. I got a friend to work on it, and after putting a new coil on it he got it running. It ran great, up until he hoocked up the PTO. It started up and ran fine, he turned on the PTO and it ran great. Then he shut the mower off, and not 30 seconds after, it blew the coil. Literally, it sounded like a shotgun went off. It was a brand new coil.

Thinking maybe we had gotten a defective coil, he pulled the coil off my old Murry. again it started up and ran fine. Mowed just fine. Shut it off and again, BANG! Another blown coil.

So before I give up and just scrap a good mower, anyone have a clue what is wrong with this thing and how to fix it?

Country Boy

By coil are you referring to a magneto, or a battery coil ignition? The former sits under the engine shroud by the flywheel with a wire attached to the spark plug, and the latter is usually mounted to the outside of the engine shroud with the spark plug lead coming off the top and two smaller wires attached to the other two terminals. If its the battery coil style, its possible you have a wiring issue whereby its dumping a ton of energy through the coil pack to ground. I'd check the wiring and look for shorts or loose ground connections. If this mower has an electric PTO, they can cause a voltage surge in the electrical system in excess of 300v when they shut down. You can install a clamping diode in parallel with the PTO wiring to prevent this voltage spike.

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'76 IH 1066 Turbo Diesel, '73 IH 766 Diesel, '72 IH 574 Utility Gas, '56 IH 350 Utility Gas, '46 Farmall H Gas, '08 Bobcat Toolcat 5600 Turbo

Nobody puts that "C" word in front of MY International!

bolensst120

Yep, its the magneto I'm refering to, and yes mine has the electric PTO.