Would this work in my 720D?

chas036

Member
I have a 720D electric start, but with no starter motor or generator or battery box. I was thinking about converting it to a 12 volt starter, but after some investigation and questions, I have to believe the 12 volt will really not have the cranking power needed.

My question is... what if I buy a new or rebuilt delco 24 volt starter like a 42MT or similar, and a "single" 24 volt marine battery that will fit in the battery box I have off a regular JD. Also I would buy a 24 volt alternator and 24 volt amp meter. Would this work?

I don't have lights or a fuel gage, so the only thing I need the 24 volts is for the starter. Having a one battery system would eliminate the complex wiring system on the tractor now. What do you think?
 
You can get 12V with plenty of cranking power if going with gear reduction.

If you want to stay 24V on starting, I would keeping both batteries and using parallel / series switch, which is about $100, leave everything else 12V.
 
(quoted from post at 20:51:25 06/19/18) You can get 12V with plenty of cranking power if going with gear reduction.

If you want to stay 24V on starting, I would keeping both batteries and using parallel / series switch, which is about $100, leave everything else 12V.

I like the 12/24 Better than straight 12V. Still going to look butt ugly with an alternator on a two cylinder .
Also going to need two group 31 batteries to crank it over .
Did no one look up the 12V specs for the MT39 , MT43 and MT50 ?
 
I looked at those specs and the 50MT has the most power, but I don't know if it would hook up to the bracket on my 720 and if the teeth on the pinion gear would match to my flywheel.
 
Found you a good deal on a starter... (should fit, crosses to a Delco 1113830.)

Slap it on, put two 12 Volt batteries in series, add a 24 Volt isolated ground alternator, touch up the wiring a little and CRANK AWAY!

A 24 Volt isolated ground alternator can be had reasonably, I see NO reason to spend another $100+ on a series-parallel switch, which adds another layer of wiring complexity in itself.

The wiring is REALLY not as complex as you've been lead to believe. When you are ready, email me and I'll forward a really helpful file.

[email protected]
Starter
 
The reason I want to go to a 24 volt starter is I found a company that sells a pony motor conversion kit and in the description they say the following:

" We have changed to a 24 volt starter and include a series/parallel switch. This will assure a faster cranking speed yet still using a 12 volt alternator and accessories. The starter is a new 40 MT starter that has a remanufactured drive. "

So I am assuming that they had a 12 volt starter originally and must of had complaints, so they changed to a 24 volts starter.

I would buy the 40 mt alone, but I don't know where I would find the correct drive gear.
 
The 12/24 switch hooks the two batteries in series for the starter during starting and parallel otherwise for all other.

Been on trucks for 50 years.

https://www.ebay.com/i/331716725375?chn=ps

We did a conversion on 8020 in late 70s.
 
The 12/24 switch allows starting with 24v but charging with a 12v alternator and running lights etc.on 12v. Since he has to buy an alternator anyway might just as well go 24v. They aren't too expensive. If he wants lights in the future they make them in 24v as well. I have my doubts about the battery having the cranking amps to do the job.
 
Maybe one of the new Nippon-Denso 12v starters has the power to spin the engine over fast enough for good starting. If someone has found that to be the case I haven't seen it on here. If not then 24v starting is the only good electric start option. If one's tractor no longer has the original split generator and function is more important than historical accuracy why not a 24v alternator?
 
. I posted the info earlier but here is is again . The highest powered 12V Nip Denso is 5Kw or 7.5HP. The Delco MT39 or Delco MT42 will make up to 7.3Kw or 9.75HP. A well tuned four cylinder starting engine is good for 14HP.
IF and IF proper cables are used and two group 31 1000CCA or better batteries are used with a MT39 or MT42. Your 720 will be a good enough three season tractor . A coolant heater will make winter starts possible .
 

With 12V you do not want "Gear Reduction"..!

You want to Spin the flywheel quick as you can, before you drop the Decompression Lever..

About all ya need is to have it roll over once with Compression..
 

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