JD U40 slow cranked but not firing

zilo · Apr 5, 2018

John Deere U40, thought I have the carburetor problem, took a few suggestion and none were work, finally gave few shots of quick start fluid, cranked the starter (slow crank, don't know why though the battery is a new one), after several times cranking, heard two laud bangs, one from the air intake pipe, the other from the exhaust pipe, and miraculously engine was started, I let it run for a while, drove the tractor through the pasture, stop at the lawn, turn on the brush hog mower saw it churning good, then I shut down every thing, and then tried to start again by it self, and again it crank but no fire. wonder what should I take, or which is not functioning, fuel side or ignition side.

Gene Davis (Ga.) · Apr 5, 2018

You mentioned it was slow cranking over. The Dubuque series tractors,(M,40,420,430), had a bad problem with poor grounding of the starter motor to the engine. It is held in place with just one large pointed setscrew and a lock nut. Remove the starter from the tractor, clean up the holding screw and where it tightens against the starter nose cone. Then run a large gauge,new ground wire from the battery post to this bolt after you install the starter back in place. Be sure and clean the area where the cable end will be under the bolt head to provide a good connection. Some times you may need another ground wire to the frame also. A poor ground connection can/will cause many issues including a poor spark issue because it is a battery ignition system. The 6 volt battery system cranked these tractor just fine as long as the cables were large enough to carry the huge amount of amps in the 6 volt and the connections were clean and tight. 12 volt size cables were not large enough to do the job. I was working for a Deere dealer when these tractors came out.

Gene Davis (Ga.) · Apr 5, 2018

You mentioned it was slow cranking over. The Dubuque series tractors,(M,40,420,430), had a bad problem with poor grounding of the starter motor to the engine. It is held in place with just one large pointed setscrew and a lock nut. Remove the starter from the tractor, clean up the holding screw and where it tightens against the starter nose cone. Then run a large gauge,new ground wire from the battery post to this bolt after you install the starter back in place. Be sure and clean the area where the cable end will be under the bolt head to provide a good connection. Some times you may need another ground wire to the frame also. A poor ground connection can/will cause many issues including a poor spark issue because it is a battery ignition system. The 6 volt battery system cranked these tractor just fine as long as the cables were large enough to carry the huge amount of amps in the 6 volt battery and the connections were clean and tight. 12 volt size cables are not large enough to do the job. I was working for a Deere dealer when these tractors came out.

Gene Davis (Ga.) · Apr 5, 2018

Can some one delete one of these posts for me? Thanks

buickanddeere · Apr 6, 2018

Your tractor has VD which does not leave enough voltage to the coil to make enough voltage to jump the spark plug gap.
The only way to positively find high resistance connections on starter cables and connections is to measure voltage drop while cranking .
I can assure you how ever that no one here has ever done that. instead of they choose to waste hours tinkering and randomly throw $$$ parts at a project until they finally luck out.
Most people regard a multimeter with the same wariness and fear used towards a coiled rattle snake .

Russ from MN · Apr 6, 2018

It's good information, some people need to read it twice!

zilo · Apr 6, 2018

I did measured the receiving end of the coil had a voltage 11.58v compared to the battery voltage of 12.63v, just don't know the way to fix it.

Tech 7 · Apr 6, 2018

Glen, how be you post a tutorial on how to use a DVOM in both dynamic and static testing? I do this regularly due to
30 years in the trade but don't have the computer skills to post the diagram(s).
Talking down to people does not help them, help is something they have come here for and you and many others have
that ability.

zilo · Apr 9, 2018

Gene, thank you for the advices on the starter problem, I went ahead cleaned the secure screw and its connecting surfaces, cranked it again, didn't work. Then I wondered if there was some wrong in side the starter, I had changed the brushes some time ago. So I took apart the starter, checked the brushes, didn't see any thing unusual, rather I saw the surface between the cone and the motor housing was dirty and greasy that I went ahead cleaned and brushed and then put it back together. And I cranked it again, this time the starter turning with a crispy sound, and I knew I solved the problem that bothered me for more than half year with your help. And I sure appreciated it.

JD U40 slow cranked but not firing

zilo

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Gene Davis (Ga.)

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Gene Davis (Ga.)

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Gene Davis (Ga.)

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buickanddeere

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Russ from MN

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zilo

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Tech 7

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zilo

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