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720 diesel problems


 
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redjohn
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PostPosted: Thu Oct 04, 2012 5:10 pm    Post subject: 720 diesel problems Reply to specific post Reply with quote

Just the other day, I had to remove the flywheel from a 720 that I'm helping a friend with, to replace the starter ring gear.
This tractor has the pony motor starter.
I re installed the flywheel making sure the v marks lined up, and the pin in the back side of the flywheel lined up with the slot , where it's supposed to go.
When I tried starting the tractor, it spun a little ways, and wouldn't turn.
Using a long screwdriver, I started turning the flywheel to try to see what could be the problem.
Just after the TDC mark on the flywheel got to the 10:00 position, I couldn't turn the flywheel any further.
I backed it up a little bit and tried again, and it wouldn't turn past 10.
I got a much longer bar, and tried budging the flywheel over, and it wouldn't go.
I am not sure if it's allright to turn the motor backwards or not.
I am at a loss, as to what could have happened.
When removing the flywheel, a friend and I used prybars on each side of the flywheel, to slowly rock it off. We did no hard prying, but used alot of wd40, and it came off rather well.
Has this happened to anyone out there? If so, what is causing my problem, and how to fix it.
I appreciate any and all answers.
 
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teddy52food
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PostPosted: Thu Oct 04, 2012 5:38 pm    Post subject: Re: 720 diesel problems Reply to specific post Reply with quote

Something on top of the piston? fuel or water?
 
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mjbrown
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PostPosted: Thu Oct 04, 2012 5:47 pm    Post subject: Re: 720 diesel problems Reply to specific post Reply with quote

I don't think it will harm it to turn it backward. I've seen them run
backward at a tractor pull with out harm.
 
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BushogPapa
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PostPosted: Thu Oct 04, 2012 6:54 pm    Post subject: Re: 720 diesel problems Reply to specific post Reply with quote


Have you held the De-Compression lever back and tried to roll it over..??
If it is Liquid...be wearing a Rain Coat, when you spin it over, to pump it out..!!

Ron..
 
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Mike M
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PostPosted: Fri Oct 05, 2012 6:00 am    Post subject: Re: 720 diesel problems Reply to specific post Reply with quote

Early or late one ? did you set the end play to .005-.010 ? If no end play that can bind them up.
Later style can have a thrust washer on the inside of the crankcase fall out of place and break.
 
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redjohn
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PostPosted: Fri Oct 05, 2012 5:08 pm    Post subject: Re: 720 diesel problems Reply to specific post Reply with quote

Sereal # is 722.... from what I can remember.
After removing the flywheel and having the problem, I went to the manual, and found out about the end play.
there were no shims behind the flywheel, so I pushed it on. Will do the right thing, setting it, after finding the real problem.
Bushhog papa, mentioned to be sure to pull the decompression lever back, and see if it turns over.
I did that, and it rolled over. My friend, who has the tractor, mentioned to me, that he pulled the little dipstick out, on the clutch side, and stuff came out.
So I checked, and sure enough, oil and antifreeze came out.
I drained the oil, which was grey, and had antifreeze in it.
So now I either have a blown head gasket, or bad head, or block.
I did roll the flywheel over, and could hear gurgling in the radiator.
As I said, I'm not real familiar with this model of John Deere, and am wondering if these engines had a bad reputation for blown head gaskets.
5 years ago, it was overhauled by someone I know, and has worked on JD stuff for years. The motor was bored out .060, and when it ran, it ran beautiful.
Upon asking more questions, when my friend first got the tractor, he had to put in a water pump, as the one in it, was leaking.
Makes me wonder if the previous owner overheated it.
Please, all who did answer, gave me good advice, but now, I could use some more. The tractor is worth saving. It's just like going on a hike. You go over one hill to get to the lake, and find out when you get to the top, there are a half a dozen more hills to go over, before you get there.
 
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BushogPapa
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PostPosted: Fri Oct 05, 2012 5:56 pm    Post subject: Re: 720 diesel problems Reply to specific post Reply with quote


If I were you, I would ask more questions on this site..

There could be a chance that the coolant is coming from the Pony engine and going into the Big Engine's Intake..
The Big Engine could have a Head Gasket leak...it is not all that uncommon..
You should make sure the Head is torqued to 275# at Operating Temp...

Ron..
 
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redjohn
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PostPosted: Sat Oct 06, 2012 7:26 am    Post subject: Re: 720 diesel problems Reply to specific post Reply with quote

From what I've read, the pony motor and the diesel engine, share the same coolant.
I'm not sure if the pony motor has a water pump, and maybe it doesn't, because it is only supposed to run for a minute or two. so it shouldn't get hot.
I'm sure I will be able to handle a head gasket change, unless there is something like specialty tools that I need. Also, if I need to remove the fuel injectors, and then how or if I have to reprime the fuel system.
Would pressurizing the radiator give me a clue?
I talked to my friend who was there, the first time the tractor started. It blew the can off the muffler (as we always forget to remove it first), and he, being on the clutch side, saw rusty water shoot out of the muffler. I was wondering where the brown crap came from that was all over the hood, generator, and frame.
 
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jd2cylman
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PostPosted: Sun Oct 07, 2012 3:38 pm    Post subject: Re: 720 diesel problems Reply to specific post Reply with quote

redjohn wrote:
(quoted from post at 16:26:22 10/06/12) From what I've read, the pony motor and the diesel engine, share the same coolant.
I'm not sure if the pony motor has a water pump, and maybe it doesn't, because it is only supposed to run for a minute or two. so it shouldn't get hot.
Would pressurizing the radiator give me a clue?
I talked to my friend who was there, the first time the tractor started. It blew the can off the muffler (as we always forget to remove it first), and he, being on the clutch side, saw rusty water shoot out of the muffler. I was wondering where the brown crap came from that was all over the hood, generator, and frame.


Pressurizing the radiator could help. But if the leak is internal, it will take a while to appear.
Pony motors were NOT meant to be run for just a minute or two. Only people who don't read operator's manuals believe in this. The pony motor was a well engineered piece of machinery. Yes, they had a water pump. This pump circulated water through the whole diesel engine besides the pony. You could start the pony and let it run to warm the big engine before starting. The worst thing people who own these diesels do, is just run the pony long enough to start the big engine. Let the pony run for a while before starting the diesel. Gas is cheap compared to a pony overhaul. A well maintained and operated pony lasts much longer. A good pony motor can idle over the diesel engine under full compression with no problem.
 
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