PTO problem?

Scag Turf Tiger zero turn -

When PTO is engaged ammeter shows discharge and never recovers. Voltage at PTO harness connector when disconnected is 13.8 + volts with increased rpm and shows the same between battery terminals. With PTO harness connected the ammeter shows a constant discharge when PTO is engaged...also battery voltage drops to 12.4 volts and never increases regardless of rpm. Is there a procedure to do an electrical test on this PTO?

You very possibly have a bad electric clutch, but you need to troubleshoot it. I assume that you have been disconnecting the electrical clutch connector, with an ohmmeter, check the resistance of the clutch coil, which if normal should be close to 2.2 Ohms. Also check from each terminal to ground, you should get an infinity reading or open circuit. The clutch coil may be internally shorted if the resistance reading is lower than 2.2 Ohms, or the coil may be shorted to ground is a reading shows on the ohmmeter when checking to ground. Also inspect the clutch wiring for chaffing thru the insulation. If you see any blue discoloration of the bearing by the bolt that holds the clutch in place, this indicated bearing overheating which in turn overheats the clutch coil causing breakdown of the coil insulation and the epoxy material it is encased in.
Mad Mackie in CT

Mad Mackie said:

You very possibly have a bad electric clutch, but you need to troubleshoot it. I assume that you have been disconnecting the electrical clutch connector, with an ohmmeter, check the resistance of the clutch coil, which if normal should be close to 2.2 Ohms. Also check from each terminal to ground, you should get an infinity reading or open circuit. The clutch coil may be internally shorted if the resistance reading is lower than 2.2 Ohms, or the coil may be shorted to ground is a reading shows on the ohmmeter when checking to ground. Also inspect the clutch wiring for chaffing thru the insulation. If you see any blue discoloration of the bearing by the bolt that holds the clutch in place, this indicated bearing overheating which in turn overheats the clutch coil causing breakdown of the coil insulation and the epoxy material it is encased in. Mad Mackie in CT

Click to expand...

This is some very good info.

My snapper has been doing the same thing.
When pto is on voltage at the battery drops to the point the battery will not charge.
I have replaced the whole charging system and no change.
I am going to go test my clutch now.

Never even thought about a bad clutch.
Thank you

Mad Mackie said:

You very possibly have a bad electric clutch, but you need to troubleshoot it. I assume that you have been disconnecting the electrical clutch connector, with an ohmmeter, check the resistance of the clutch coil, which if normal should be close to 2.2 Ohms. Also check from each terminal to ground, you should get an infinity reading or open circuit. The clutch coil may be internally shorted if the resistance reading is lower than 2.2 Ohms, or the coil may be shorted to ground is a reading shows on the ohmmeter when checking to ground. Also inspect the clutch wiring for chaffing thru the insulation. If you see any blue discoloration of the bearing by the bolt that holds the clutch in place, this indicated bearing overheating which in turn overheats the clutch coil causing breakdown of the coil insulation and the epoxy material it is encased in.
Mad Mackie in CT

Click to expand...

Thanks for the reply...I will check that this morning and let you know what was found.

Meter shows open when each lead of the PTO harness is looped to ground. Both leads together read 00.6 ohms.

You need a new clutch as 2.2 Ohms is the lowest acceptable resistance for a 250 FTLB or higher torque clutch on a Turf Tiger.

On lower torque rated clutches the resistance range is 2.8-3.2 Ohms. As the torque ratings increase, the resistance range decreases down to 2.2 Ohms with very little variation for the Ogura GT 3.5 and Warner clutches.
A clutch that is out of adjustment, meaning that the air gap is to much and out of spec, the resistance reading may be within limits, but the amperage draw during operation will be higher than normal as the electrical demand on the clutch coil increases to keep the brake disengaged.
Although not common, a clutch coil that has shorted to ground can severely damage an engine. The path of least resistance of a shorted to ground coil is thru the crankshaft, then the main bearings where serious damage can occur. I suspect that this condition is frequently miss-diagnosed as I have heard comments from folk that they had recently replaced the clutch and then the engine failed. I have actually had an engine here in my shop that I tore down and was able to see the damage to the main bearings from a grounded clutch. The bearings were insert type and being a less noble metal than the crankshaft and engine block, deteriorated to the point where oil pressure dropped to low and the engine seizes from lack of lube.
Clutch bearings are another consideration as one bearing turns all the time the engine is running and the pulley bearing stops turning only when the PTO is in the on position. They can get too hot from lack of lube and or moisture intrusion and cause clutch problems and failures.
Mad Mackie in CT:laughing::biggrin::smile: