My Tractor Forum banner

1 - 7 of 7 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
PTO clutch problems. Initial start-up all works well. Turn on PTO switch and the mower deck runs great. After running for a period of time and I need to disengage the PTO is when the problem starts. When I turn on the PTO switch nothing happens. After the mower has sat for a period of time (cooled down) the PTO will once again engage. I have looked at the wiring diagram and can not identify anything that could cause a problem i.e. heat sensor etc.
Any suggestion to correct my problem would be appreciated.
Paul
 

·
Moderator
Joined
·
2,415 Posts
Welcome to MTF, I moved this to the LGT/GT section for you for better response.

Have you checked continuity at the switch when it's hot?
 

·
Premium Member
Joined
·
7,667 Posts
An electrically controlled PTO is basically an electromagnet that controls a clutch. Most of the older ones had an adjustable air gap that you adjusted by loosening a bolt or nut and then used a feeler gauge, similar to gapping a spark plug. There is usually a narrow range of tolerance for that gap to ensure that the PTO engages properly without dragging when disengaged. It may be that the air gap is close to the edge of the allowable tolerance when cool and it increases when hot to the point that it won't engage until it cools down again.

It could also be that the insulation of the windings of the coil of the electromagnet is breaking down. The insulation is most likely a very thin coating of varnish or similar material and whenever the PTO is on electricity is flowing through the coil, which causes it to heat up, which in turn causes the wire to increase in diameter slightly. Then when it is shut off it cools back down and the wire decreases in diameter. Doing this repeatedly over hte years will cause the insulation to get micro cracks in it that widen when the wire is warm and enlarged and when the wire cools down and contracts the micro cracks close up. As this goes on over time the insulation begins to break down and flake off at the edges of the micro cracks so that the gaps of uninsulated wire get larger and larger over time, increasing the chance that the gaps from one winding will line up with the gaps of the next winding causing a slight short (one winding out of several hundred), which is worse when it is warm and which closes up again when cooled. As more time goes on more of these slight shorts occur to the point where it won't allow enough magnetism to be generated to engage the PTO clutch when warm until it cools down and the micro cracks close up.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #7
An electrically controlled PTO is basically an electromagnet that controls a clutch. Most of the older ones had an adjustable air gap that you adjusted by loosening a bolt or nut and then used a feeler gauge, similar to gapping a spark plug. There is usually a narrow range of tolerance for that gap to ensure that the PTO engages properly without dragging when disengaged. It may be that the air gap is close to the edge of the allowable tolerance when cool and it increases when hot to the point that it won't engage until it cools down again.

It could also be that the insulation of the windings of the coil of the electromagnet is breaking down. The insulation is most likely a very thin coating of varnish or similar material and whenever the PTO is on electricity is flowing through the coil, which causes it to heat up, which in turn causes the wire to increase in diameter slightly. Then when it is shut off it cools back down and the wire decreases in diameter. Doing this repeatedly over hte years will cause the insulation to get micro cracks in it that widen when the wire is warm and enlarged and when the wire cools down and contracts the micro cracks close up. As this goes on over time the insulation begins to break down and flake off at the edges of the micro cracks so that the gaps of uninsulated wire get larger and larger over time, increasing the chance that the gaps from one winding will line up with the gaps of the next winding causing a slight short (one winding out of several hundred), which is worse when it is warm and which closes up again when cooled. As more time goes on more of these slight shorts occur to the point where it won't allow enough magnetism to be generated to engage the PTO clutch when warm until it cools down and the micro cracks close up.

My problem was the Airgap. I made the adjustment and all is well.
Thank you for the advise.
Psul
 
1 - 7 of 7 Posts
Top