Craftsman GT18 Electrical help needed

D

Dpregs

Well-Known Member
Member
Hey guys,
I am in the process of getting my two Craftsman ready to sell, even though I am torn because I love the look and sound, but the barn can only hold so many tractors. And with a JD355D on the way....somethings need to go.

Well, I decided to fix the leaky oil sump gasket on my GT18 917.255910 and do a tune up. Oil has been slowly leaking since I got it, and I had the gasket on hand, so I did that. I put in a new battery and then I started to see smoke emanating from the engine shroud around the flywheel! I ripped the battery cables off and took a breath. I looked to see what I could, but to no avail. SO, I hooked up battery and tried to start the machine. Fired right up and no smoking now. I thought I was good. All of a sudden I see smoke coming from behind the panel! Disconnect again and I see that it is the Diode assembly coming from the stator that is fried. This is the second time. The first time it happened last year I chalked it up to age. Instead of buying a new $60+ diode assembly, I made my own. It worked fine all last year. So, to make sure I didn't kill the stator, I started up the tractor and tested the VAC coming from the stator, was getting 30vac at max throttle and around 24vac at low throttle. So, to me that looks to be in spec.

So, what could have fried the assembly? I short somewhere? I short in the stator, but why do I get good readings? A bad setup by me? I'm lost and need to fix this thing to sell it! Any help appreciated!

oh, and if I need to pull flywheel....advice because I couldn't get damn thing off last time I tried.

Here is some additional info and pics:
Tractor: 917.255910
part that is fried: 106315x
Diodes purchased for building new assembly: 10SQ045 10A 45V Schottky Diodes, for Solar Panel / Wind, Rectifier, 10AMP
Electrical Schematic: File attached :1003362-026
Alternator Setup: File attached 1alternator_id-004
Tri-Circuit manual:
tri_circuit.jpg

Pics of old Diode assembly:
old_diode_1.jpg old_diode_2.jpg old_diode_3.jpg old_diode_4.jpg

New Diode assembly (before current issue):
new_diode_1.jpg new_diode_2.jpg new_diode_3.jpg
 

Attachments

What all was on when it did this?
Running or just on?
Lights on?
PTO clutch on?

Do you have an ohm meter?

Check the ign switch and make sure not short from L to M.
Also, you should be able to find the ohm reading of the alternator.

As for flywheel removal, 3 hands.
Two to put oposing prybars under the flywheel and one to hit the end of the crank with the nut flush with the end Sharply.
I use a brass hammer, but have seen other.
 
Thanks for the reply.

Nothing was running, just plugged in the first time it started to smoke. Then while it was running.

I'll check the ign switch first thing and see if it is there.

Let's hope I don't have to pull the flywheel :)

Again, thank you and I'll report back later.
 
Maybe a stupid question, but how do I check ohms on alternator? It's an ac alternator and putting out around 30vac
 
You might have a high resistance short in your wiring. Look for corrosion next to a wire laying on metal or other conductive materials. These will eventually damage electrical components but will not show signs of overheated wires.
 
Sorry I didn’t see your questions, but you got it.
It’ll be something simple if it’s a wire. Pinched under tins or rubbing on something.
Hope it’s not an alternator.
 
If you are getting 30VAC off the stator it is fine, there is a short somewhere past the diode assembly causing it to fry. Couple quick checks.
1. Are the diodes orientated correctly? One will provide Positive to charge the battery, the other will be reversed to provide for the lights.
2. Disconnect the diode assembly and carefully measure the wire going to the key switch. Key off = 0 volts, key on = battery voltage.
3. follow the wires, look for a short.
Alternator - Diode - Amp meter - key switch - Battery.
PS I make my own diode assembly's also.
 
Went back and looked at the diode assemble, looks like only one blew, can you tell if it fed the light or charging circuit? Could be a short in the lights also.
 
Great advice guys and much appreciated! I have been too busy to get to it with so much going on. I'll open up the diode wrapping and see first, great place to start!
 
So, the kid decided to take a nap so I ran to my work station and ripped open the assembly I made.

Interesting is that it looks to be same diode as the first time. I don't think it's the lights because they weren't hooked up when it fried. The connector has a "2" on it, I think that's the lights. Also, I'm 99% sure I have diodes in right direction.
20190417_081108.jpg 20190417_081116.jpg
 
At the tractor and not 100% sure what im doing with multimeter, but I tested continuity of ground from switch to chassis and was fine. Continuity of single wire off alternator fine. But, when I switch meter to ohms I get 0.0 between grounds and on single wire from alternator to a ground 0.5.

Like I said, no idea what I'm doing, just trying things.
 
Ok, on the diode that blew, look at which pin it goes to inside the 2 pin connector. follow that wire and tell us where it goes. Based on the diagram it will either be a Red wire going to the ignition switch, or a Orange wire going to the light switch.
The diodes must be reversed (again looking at the diagram).
 
Some things to check.
1. Ignition switch mat be shorted (L to G) in the RUN position.
2. AMP meter may be shorting the B terminal. (Is the fuse good?)
3. The PTO Switch may be shorting Terminal A to ground.
4. Related to a bad PTO switch, the PTO wires may be shorting to ground.

I have dealt with 1, 2, and 3 all being bad switches before.
 

Attachments

I got to thinking about this some more. The diode may be reversed, if it is... it will short the battery to ground through the alternator coil.
I can take some measurements off mine tonight to verify the correct diode orientation and post those pictures.
What type of OHM meter do you have (Analog or Digital)? I have both and can show the readings with either.
 

Attachments

1. Fuse is good - 30amp
2. I checked ignition switch other day and all had good continuity
3. How do I check for bad switch?

I have digital meter
 
You must log in or register to reply here.
Back
Top