runaway deisel engine on 720

Quinton Hornsby · Nov 8, 2014

Where do you start? Is it the governor? Throttle seems to not help even in shutting the engine down.

buickanddeere · Nov 8, 2014

Th service manual devotes several pages on how to set up the throttle, governor and rack linkages.
Every adjustment is vital and must be precise.
Fortunately the nice folks at 1-800-522-7448 have the operators and service manuals on CD and hard copy.
The parts book is online at Mother Deere's site.http://jdpc.deere.com/jdpc/servlet/com.deere.u90490.partscatalog.view.servlets.HomePageServlet_Alt

Tim(nj) · Nov 8, 2014

Is it using oil excessively? A diesel can get enough crankcase oil into the cylinders to fuel a runaway. I don't know of any JD two cylinders that have done it but I've seen other brands of engine do it.

Aussie Ken · Nov 8, 2014

The return spring on the fuel rack could have broken -which stops the rack from returning to idle position-take the cover off of the fuel pumps to see if there is movement of the rack with the throttle, you can also see the spring on the right side of rack
Has it sat a long time? the rack could be sticky from fuel deposits -

John Deere D · Nov 8, 2014

Do what ever it takes to purchase JD service manual SM -2020 (12-57). There are many possibilities .
Bob...

cushman · Nov 8, 2014

Another possibility, is the governor weights came off the governor shaft.

Gpower · Nov 8, 2014

Pull the top cover, if its an early 720 (green dash) its 2 bolts. The later black dash will have the return line fitting to remove also. Look on the right side and check to see if the spring and follower is still in place. (aussie ken mentioned this.) Also pull the throttle all the way back, pull the stop out and move the throttle lever all the way back. Check to see if the rack rods are moved all the way over towards the left (flywheel side) The spring should be pushing them over if its in there. I will venture to say it is not since your experiencing the runaway symptom. Of course, do all this with the engine off!

MT RON · Nov 8, 2014

I bought a 720 that the guy said had run away, the push rods were bent.Both weights had came off the governor.Also apparently at the same time the governor idler shaft broke off and of course ate up a bunch of the gear teeth.I was able to repair everthing and now its a sweet running tractor,good luck.Ron

DONMYEIL · Nov 9, 2014

Has the pumps been rebuilt ? We had a mechanic actually bend the control rack shaft and we had a runaway. Older mechanic was there to decompress and shut it off . BEFORE STARTING ANY OF THESE 2-CYL dIESELS CHECK THAT THE DECOMPRESSION LEVER WORKS .AND DONT PUT YOUR HAND OVER THE INTAKE UNLESS YOU WANT THE MEAT SUCKED OFF.

buickanddeere · Nov 9, 2014

(quoted from post at 12:14:19 11/09/14) Has the pumps been rebuilt ? We had a mechanic actually bend the control rack shaft and we had a runaway. Older mechanic was there to decompress and shut it off . BEFORE STARTING ANY OF THESE 2-CYL dIESELS CHECK THAT THE DECOMPRESSION LEVER WORKS .AND DONT PUT YOUR HAND OVER THE INTAKE UNLESS YOU WANT THE MEAT SUCKED OFF.

I choked down the 435's run away 2-53 when the govenor failed using my bare hand. Using the same hands to thumb this message .

M-MAN · Nov 9, 2014

Glenn;
You were very lucky. I remember years ago when I got my 3-53 and dropped a valve. An old mechanic told me to put it back together and set everything exactly by the book. Then have the book in my hand when I fired it up just in case I needed to shut down a run a way. Mabie two cylinders don't pull as hard?

runaway deisel engine on 720

Quinton Hornsby

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buickanddeere

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Tim(nj)

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Aussie Ken

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John Deere D

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cushman

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Gpower

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MT RON

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DONMYEIL

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buickanddeere

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M-MAN

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