JOhn Deere 730 diesel starter problem

Raymond Rauch · May 9, 2018

Rebuilding a JD730 diesel that has been in the family since new. For the last 20 years it has been started by coasting it as dad did not hook up the starter. Easier I guess. Since I am rebuilding it I wanted to make it right. It had a 24 volt starter on it that was never used that I know of. I took it to a shop and they converted it into 12 volt and I used 2-0 battery cables to wire it up. The starter will roll the engine with the decompression pedal pushed but when you let up it immediately stops rolling and does not fire. I can coast start the tractor and it starts up just fine. I am thinking the 12 volt starter doesn't have enough torque to roll the engine to start. Any thoughts or help would be great. Should I go back to a 24 volt starter or do I have another problem. Should I use a 4-0 battery cable or is 2-0 large enough. Thanks

John Deere D · May 9, 2018

Years ago (1975?) I installed a 12 volt starter on my then JD 'R'........Total waste of time....good experiment:

Installed a 24 Volts starter from a Caterpillar G333 Engine....Engine would spin over so fast Neighbours eyes popped out of their sockets:

Bob....

buickanddeere · May 9, 2018

What is the CA or CAA capacity of the battery . Along with the group size ? Battery negative cable is bolted down where ?

Raymond Rauch · May 9, 2018

CA is 1000 and the ground is clamped to a 3/8 bolt just behind the fly wheel. right in front of the right side brake assembly.

I did a resistance test on the battery with my ohm meter and got 12.8. I then tested the starter and got 12.8. tested the starter when rolling the engine with decompression pedal pressed and got 9.8

buickanddeere · May 9, 2018

. That would be a voltage test . First one I have ever seen anyone do here in 15+ year’s on this site while cranking.
Voltage measures between the battery posts ? Or between the + post on the starter and the starter body ?

MSM · May 9, 2018

One battery won't spin it on compression,especially if it is cold. At minimum 2 group 31's

erskine2017 · May 9, 2018

Why not take it back to the shop and have them put new 24 volt fields in it? How will you charge your 12 volt battery with a 24 volt generator and regulator? You will also need a 12 volt solenoid for the starter.

buckeye al · May 9, 2018

If you check the voltage by connecting to the BATTERY POSTS while cranking and you see 11.6 (a number pulled outta my hat) that means (11.6 at the batteries minus 9.8 at the starter's post) you're losing 1.8 volts in the battery clamps and cables. If your cables have 800 Amps passing through them you're loosing almost 2 horsepower because of that 1.8 volt difference. That's a big loss. You MAY be loosing a good amount of that voltage at the skinny little 3/8" "ground" bolt connection. A bigger bolt closer to the starter MAY help. A 7/16 or 1/2 bolt that squeezes the cable end between the main case and a washer (as opposed to a bearing cap and a stud/nut) may help there.

If you see 9.8v delivered to the starter and 9.8v at the battery posts then your cables and clamps are doing THEIR jobs just great! That indicates the battery or batteries are either weak or plain old overloaded!

I'm thinkin to push that 6" piston to TDC against the 16:1 compression ratio takes about 6000 pounds of force! To do it at 200+ RPM (recommended cranking speed for these engines) takes some serious HP which is asking a lot of a 12 volt starter. Some of the reasons why Delco designed and recommended the 24 volt cranking circuitry to Deere & Company to electrically start their 2 cylinder Diesel tractors!

Maybe that helps a bit?

buickanddeere · May 9, 2018

(quoted from post at 18:58:35 05/09/18) If you check the voltage by connecting to the BATTERY POSTS while cranking and you see 11.6 (a number pulled outta my hat) that means (11.6 at the batteries minus 9.8 at the starter's post) you're losing 1.8 volts in the battery clamps and cables. If your cables have 800 Amps passing through them you're loosing almost 2 horsepower because of that 1.8 volt difference. That's a big loss. You MAY be loosing a good amount of that voltage at the skinny little 3/8" "ground" bolt connection. A bigger bolt closer to the starter MAY help. A 7/16 or 1/2 bolt that squeezes the cable end between the main case and a washer (as opposed to a bearing cap and a stud/nut) may help there.

If you see 9.8v delivered to the starter and 9.8v at the battery posts then your cables and clamps are doing THEIR jobs just great! That indicates the battery or batteries are either weak or plain old overloaded!

I'm thinkin to push that 6" piston to TDC against the 16:1 compression ratio takes about 6000 pounds of force! To do it at 200+ RPM (recommended cranking speed for these engines) takes some serious HP which is asking a lot of a 12 volt starter. Some of the reasons why Delco designed and recommended the 24 volt cranking circuitry to Deere & Company to electrically start their 2 cylinder Diesel tractors!

Maybe that helps a bit?

All good points . The V4 starting engine made 14HP and used most of it in cold weather . 800 amps at 9.5 volts will only make at most 7HP at the starter .

mjbrown · May 9, 2018

This is an interesting but expensive experiment. I too traveled down this road. My pos and neg cables were/are attached to the terminals on the starter motor. I'm not sure why
you have ground to the block unless they made that change in your starter. 12v could never build up enough momentum in the flywheel to kick the engine over on compression.
I tried two 8v batteries in series and that got the flywheel spinning just fast enough to usually get one compression and a start in summer. I gave up and went back to two 12v
batteries in series. I did not have the starter converted back to 24v and it has lasted many years. When I push the starter button it fires up right now! I went through all this
because a previous owner had removed all the original 24 system and had a 12v alternator charging 24v with some sort of thermal cut out. I thought I could do better. A fellow
named Mike Manley who used to be on here claimed he had it figured out for 12v. He sent me pictures and diagrams on how he did it. I very much appreciated the help he sent
me but I never got it working right. Mike passed away quite a few years ago. Perhaps some of his old posts are still in the archives but I think you will be back to 24v.

mjbrown · May 9, 2018

I should clarify. The previous owner removed the split generator and the wiring for that system but kept the 24v starter.

buickanddeere · May 10, 2018

There is the classic 24V start/ 12V run relay . Allows standard 12V accessories and a high HP start.
Then again if the tractor had been left the way it should be and just refurbish the starting engine . There would not be all these electrical mysteries and no starting .
Most people puzzled by the starting engine and think that an electric conversion is quick, fast , easy and cheap . These people become well acquainted with hills and pull starting.

buckeye al · May 10, 2018

It occurred to me last night driving home I had made an error in my calculations! That 6000 pound force I mentioned is way off! With 300 PSI compression on a 6" diameter piston, the force would be more like 8500 pounds not 6000!

Sorry for the error.

rustcollector · May 10, 2018

I have a 730 diesel with factory 24 volt system. If batteries are charged, will start in 20 degree F weather with only one complete revolution of diesel after compression release is turned off and throttle advanced. Would suggest that you go back to 24 volts following John Deere's electrical schematic exactly.

buickanddeere · May 11, 2018

(quoted from post at 21:25:59 05/10/18) I have a 730 diesel with factory 24 volt system. If batteries are charged, will start in 20 degree F weather with only one complete revolution of diesel after compression release is turned off and throttle advanced. Would suggest that you go back to 24 volts following John Deere's electrical schematic exactly.

Delicious Remy makes a 12V PM gear reduction starter that develops a significant amount of cranking power . http://www.delcoremy.com/Starters/Find-by-Model-Family/39MT-Gear-Reduction-Starter

erskine2017 · May 11, 2018

Deere used a 24 Volt system for 11 years. What is wrong with using the system that came with it?

Jgrady · Jun 27, 2018

The 39 MT is an outstanding product. But Delco Remy only produces an 11 and 12 tooth pinions. I have made an #3 SAE flange and 13 tooth gear to modify a Delco Remy 39 MT starter. You can use 1 12 volt group 31 battery however 2 is best.

WGM · Jun 27, 2018

To prove the modifier is smarter than the JD and DR engineers.

Tx Jim · Jun 28, 2018

(quoted from post at 18:50:02 05/11/18) Deere used a 24 Volt system for 11 years. What is wrong with using the system that came with it?

Because 12 volt starters are stronger & 12 volt batteries have more CCA than when 730 was built 58 years ago PLUS 12 volt system is a lot simpler than 24 volt system & not as prone to fires caused by electrical shorts.

buickanddeere · Jun 28, 2018

(quoted from post at 21:43:30 06/27/18) The 39 MT is an outstanding product. But Delco Remy only produces an 11 and 12 tooth pinions. I have made an #3 SAE flange and 13 tooth gear to modify a Delco Remy 39 MT starter. You can use 1 12 volt group 31 battery however 2 is best.

The max amount of cranking motor power on a 1000CCA group 31 battery is about 6-1/2 HP in warm weather

JOhn Deere 730 diesel starter problem

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