PTO trouble when hot, 18 mag
 

The 18 mag in my 682 has been great. Just this evening however after getting nearly all the yard done, I turned off the PTO to move yard toys out of the way. Got back on and no dice, PTO won’t engage. Checked fuse, looked ok changed anyways. No go. Hearing clicking at relay. After a while it finally engaged. Finished yard and could smell faint plastic burning. It’s at fuse under the dash. You can see the distortion in the plug in the picture, got hot and was melting. What’s the issue here?

I would think you have a high resistance connection somewhere.

wrong fuse or holder type?, the oem ones are hard plastic.

check air gap on clutch brake if out too far it has to pull harder to engage

Thanks for the help. MikeMasheris- that sounds plausible, I did the front crank seal over the winter and checked air gap then, suppose it could be out, thanks

X2 on the air gap!

I respectively need someone to explain to me how that happens.

In my way of learning, the coil of the PTO is an electromagnet that gets energized when 12 volts and ground are applied to it's windings.
The resistance of the coil windings is fixed and never changes, therefore the current going through it has to remain constant. current = voltage divided by resistance. (I=E/R).
So how does changing the air gap of a passive part in the game cause more current to flow thru the coil, whether it is a thousandth of an inch or a thousand miles. I'm probably wrong but I need it explained to me.

My money is on the windings shorting out, thereby lowering the coil resistance, thus sucking more current and heating the fuse and wire.

The windings are like that of a transformer, if you remove a transformers core the windings will overheat.
Same as the induction windings of the pto.
remove the disc and the windings overheat.
The disc becomes the core.
I'm sure google could explain the rule of physics that applies to the induction of a current in a core related to the turns & wire size.
off the top of my old grey head I can't remember the ohms of the pto induction coil when good.
but over 50% of the time, adjusting the air gap cures his symptoms and the coil is good.
Not to say that coils don't go bad, seen a few for sure.:bigthink:

I can agree with your theory, but this is not a transformer. Widening the air gap is not removing any core.

Per Mr. Bedells drawing, applying power to the field coil (#1) turns the drive disc (#2) which does not move (except for rotation with the crank) into an electromagnet. When that happens the, the driven disc (3) which has the pulley, is attracted to the drive disc, closes the air gap and rotates with the rotating drive disc and you cut grass. Sorry, but I just can't see how a change in the air gap can affect the amount of current flowing through the field coil.

My take on the clutch troubles is when the air gap gets too wide the clutch slips a small( probably unnoticed) amount, makes extra heat, raises the resistance, heats up the wiring as well as the epoxy on the clutch coil itself and before you know it the wiring, connections, and coil are all comprised. I’ve seen new clutch assemblies put on and fail a short time later just because the gap was never adjusted. I know you didn’t ask my opinion but there it is