john deere 550 dozer won"t start.

[museum quality]

Do you have a relay that operates the starter solenoid primary current?
What do you mean by "solenoid ground terminal"?
I have never seen an isolated ground solenoid on a tractor.
The faint humming sound could have been the brushes on the comm or the starter windings.

Yes there is a relay that is functional and brings a live current to the solenoid. the solenoid has a large wire connection which is clearly hot with a large red wire coming in and one going out to the alternatorthe solenoid also has a small stud that(I think is neutral) which has two wires. one coming in from the relay and one going out to a stud mounted directly on the motor housing. the stud that leads to the motor housing was hot to the touch but was not hot on the motor housing stud.

[Bob Rooks]

Yes there is a relay that is functional and brings a live current to the solenoid. the solenoid has a large wire connection which is clearly hot with a large red wire coming in and one going out to the alternatorthe solenoid also has a small stud that(I think is neutral) which has two wires. one coming in from the relay and one going out to a stud mounted directly on the motor housing. the stud that leads to the motor housing was hot to the touch but was not hot on the motor housing stud.

I believe that relay also supplies current to the alternator field windings, which control it's charge rate. There is no "neutral" it's all DC (Direct Current).
Positive = (+) Plus and Negative (ground) = (-) Minus. The small terminal on the solenoid is the (+) side of the solenoid motor windings that draw in the large high-current starter motor contacts, which are the two large terminals on the solenoid. The solenoid motor is grounded through the case to the engine block.
Assuming your batteries are of the correct amperage capacity, and all electrical connections are mechanically sound, I believe you are going to have to remove and disassemble the starter. We can go from there. The fact that the ground wire to the engine block was warm pretty much says everything is working OK except for the starter.

[museum quality]

Thanks for the advise, I will take it off and also order a service manual on ebay. I never took the time to really learn about the mechanics of this beast and in a better economy I would hire it all out to a tech. and stick to doing what I know best. JG

[JasG]

One last test you could try if you have a heavy duty set of jumper cables. Connect 1 side to the starter where the cable from the solenoid connects or the stud that goes from the solenoid to the starter. Then touch the other end to the positive terminal on the battery. Make sure you are only touching the points listed. If your starter is good it should spin over. If not then you will know for sure.

If your jumper cables aren't heavy enough they will get hot very quickly.

[Varmint1]

I haven't worked on one of these in years, is it a 12 or 24 volt system, I can't remember, have you had the batteries out lately to be charged?

[museum quality]

love the Reagan quote as well as the advice. I will certainly try that the next time I am with the machine. l Iooked at it today and dread the idea of taking the motor out. I can see two of the bolts holding it on but there is very little room to work them out as it now stands. The third bolt is underneath and may require the bottom plate to be removed.
The whole engine may need to be lifted out to get at them. Its all unchartered territory for me. Happy Thankgiving.

[museum quality]

Im pretty sure its twelve volts and the batteries are new and live. In case this dozer needs to be transported to a shop, is there a way to get it jump started in order to get it on a truck without the starter/motor ?

[Bob Rooks]

Im pretty sure its twelve volts and the batteries are new and live. In case this dozer needs to be transported to a shop, is there a way to get it jump started in order to get it on a truck without the starter/motor ?

You can try a screwdriver between the small terminal on the solenoid and the large solenoid terminal with the battery cable on it. If that doesn't produce results then try the screwdriver between the two large terminals (watch out for arc flash). If this doesn't produce anything, then it can't be jumped.
Dumb question, but does the engine turn over by hand? Can you bar over the flywheel or get a socket on the front of the crankshaft?

[JasG]

Im pretty sure its twelve volts and the batteries are new and live. In case this dozer needs to be transported to a shop, is there a way to get it jump started in order to get it on a truck without the starter/motor ?

If you try what I put up with the jumper cables it should start if the starter motor is good. At least it would tell you if it is the starter or something like the solenoid.