I swapped a Predator 670 engine into a John Deere 757 zero turn. I started the engine, engaged the pto, cut some grass, but the engine was smoking very badly, so I removed the engine, exchanged it and the new one runs great but when I turn on the mower it dies. The belts are free, the clutch shows about 2 ohms, no grounds. When I disconnect the wire plug to the clutch the engine continues to run when I turn the pto on. The battery voltage drops about 1 volt when I hit the starter. Oddly, the battery voltage does not drop even though the pto starts to turn the belts a little before the engines quits. I attached the wiring diagram form the manual if that helps. I am at my wit's end!
Fuddyduddy1952
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Here's how I would troubleshoot it. The PTO clutch has two leads, black and blue wires. I'd unplug it. Then (not running of course) use two clip leads, one to ground, other battery +positive. Just for a second or two and you should hear it click (engage) each time it gets power. Now I'd start mower and connect again. Caution! Of course you have to be careful doing this! Harbor Freight sells a clip lead set...you may want to make long ones so you can try it while in seat.
If this works and engine doesn't cut off you know clutch and drive system is fine.
Then looking at diagram next is PTO relay. It gets power from PTO switch, however, all those safety switches like brake, seat and control lever switches must be good and engaged to work otherwise motor cuts off.
My guess is it's one of the safety switches either bad or not engaging as it should.
If this works and engine doesn't cut off you know clutch and drive system is fine.
Then looking at diagram next is PTO relay. It gets power from PTO switch, however, all those safety switches like brake, seat and control lever switches must be good and engaged to work otherwise motor cuts off.
My guess is it's one of the safety switches either bad or not engaging as it should.
WranglerX
Super Member
As Fuddyduddy says, check all the switches....
I have done all the checks suggested here as well as other internet sources, with no answers. Today I powered the clutch on with a separate battery, (not connected to the tractor) and it still shut down the engine. The clutch spun until the engine stopped. (belt was off) This is my son's mower, so I can't scrap it!
oldnslo
Super Member
Is the engine stopping like turned the key off or lugging and dying?
From what you describing with separate battery I suspect lugging and dying. If yes to the lugging then you have other issues like mechanical binding in clutch or deck if belt is connected. Possibly bearing going bad in clutch, etc.
If deck is connected could be engine running a little lean or governor is a little sluggish on response, etc.
From what you describing with separate battery I suspect lugging and dying. If yes to the lugging then you have other issues like mechanical binding in clutch or deck if belt is connected. Possibly bearing going bad in clutch, etc.
If deck is connected could be engine running a little lean or governor is a little sluggish on response, etc.
Richard001
Veteran Member
In post #6 the OP said that the belt to the deck was not in place.
Richard001
Veteran Member
When you applied power to the clutch from a separate battery, was the connector that goes to the clutch still connected ?
No, it was not connected the jump box was completely isolated.
It was like turning the key off.
Fuddyduddy1952
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That blows my mind.
The clutch is an electromagnetic with a pulley.
It freewheels until you apply power which energizes magnet...a "pulley clutch".
Apply power from another battery, no belt on it and not plugged in, simply power to it from another battery which kills the motor?
At this point I'd remove it from your mower. Then lay it on ground and try it, another battery and mower battery.
What my guess is when you remove it...carefully inspect wiring harness. I bet you'll find a wire with skinned insulation. So when PTO clutch is engaged it twists a little bit (a small chain keeps it from turning too far). It twists and is shorting out a wire that's pinched or skinned which cuts engine off.
The clutch is an electromagnetic with a pulley.
It freewheels until you apply power which energizes magnet...a "pulley clutch".
Apply power from another battery, no belt on it and not plugged in, simply power to it from another battery which kills the motor?
At this point I'd remove it from your mower. Then lay it on ground and try it, another battery and mower battery.
What my guess is when you remove it...carefully inspect wiring harness. I bet you'll find a wire with skinned insulation. So when PTO clutch is engaged it twists a little bit (a small chain keeps it from turning too far). It twists and is shorting out a wire that's pinched or skinned which cuts engine off.
dstig1
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I like where Fuddy is heading. Somehow I'd guess powering the clutch is grounding the engine winding/plug whatever it is like the typical kill switch on small engines.
I still can't understand how any kind of a problem with the clutch can shut down the engine without it being electrically connected to the tractor (separate battery)
Fuddyduddy1952
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Any engine with a magneto ignition the coil like this has a 1/4" terminal. If unplugged engine runs until it runs out of gas. Connect to ground kills spark, engine cuts off.
Engaging PTO the clutch moves a bit until chain stops it from turning so it works. If it turns enough to ground that kill wire that kills ignition.
Only thing I can come up with given all the testing OP has done. It's all that's left...that or PTO switch itself is grounding that magneto terminal.
Engaging PTO the clutch moves a bit until chain stops it from turning so it works. If it turns enough to ground that kill wire that kills ignition.
Only thing I can come up with given all the testing OP has done. It's all that's left...that or PTO switch itself is grounding that magneto terminal.
Williy
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If that wire goes to the spark plug to short it out and its killing
the engine I would check for it to be shorted out maybe with
all the movement the wire wore a hole and its shorted???
willy
the engine I would check for it to be shorted out maybe with
all the movement the wire wore a hole and its shorted???
willy
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Okay, here's the skinny. When I installed the Predator in the John Deere, I turned the PTO clutch around to allow the belts to line up. The magnetic hub is close to the engine and is shutting the engine down. (no idea why) I have some room to put something to block the magnetism, but I have to find out what works. It's either that or extend the engine shaft about 2 inches, but that's scary!! Thanks for the suggestions.
Fuddyduddy1952
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If PTO clutch is unplugged, then there isn't any magnetism. Engine running if you turn PTO switch on and motor dies then it must be grounding out ignition magneto coils.
When I installed the clutch the correct way with the magnetic hub away from engine, then energized it the engine continued to run. It's only with the hub close to the engine that it shuts down. I repeated the test to be sure and got the same results, got to be magnetism.
dstig1
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Could the magnet be pulling on the kill switch or a terminal and causing it to activate and ground the spark? Can you see if the switch makes ground connection when you trigger the PTO? Maybe ohm from the open side of the switch to engine ground and then watch the ohmmeter as you push the PTO button.
