JD 755 CUT Governor Issues?

[michahicks]

Re: JD 755 CUT Governor Issues? Follow up...

Since writing last I ordered out a set of gaskets and both the starter and main springs within the governor - per my plan at the time. They arrived at the dealership, and the main spring appeared similar to the original, but was a little bit shorter. Maybe 1/8" or so? The "starter" spring was completely different, with more turns/coils and shorter than the original. Against my better judgement (supecting the new starter spring would be way too wimpy), I went ahead and installed both.

It wouldn't even stay running once started. It would die as soon as you you released the key. My best guess as to what was going on with this new starter spring is that there is so little tension available from it, as soon as the egine starts spinning the flyweights, they spread fully and shut the fuel off - just as if it were overspeeding.

Now, completely frustrated, I'll just leave this situation described as disappointing?

I disassembled it AGAIN, and without changing ANYTHING else, I reinstalled the spring I had stretched earlier. Now it starts and runs - though I don't believe it's right yet.

It would appear there's some sort of mismatch between the installed flyweights and this spring and no guidance anywhere for help? Any other thoughts/ideas?

-Al

 

[michahicks]

Re: JD 755 CUT Governor Issues? Final update, problem identified/repaired!

It's been a while since posting last, but wanted to leave this for anyone with a similar problem following this at a later date -

As suspected, it wasn't my imagination, unrealistic expectations, or a diesel engine designed to develop it's power at high rpm only at all. It WAS a governor issue at the root of the evil haunting me.

Still unable to put this issue down, I was going back through the manuals and discovered a section devoted to "Theory of Operation" in the Component Technical Manual (CTM) that I hadn't seen before. There's a section there regarding governor operation, which broke the governor's operation down to the starting and idle phases, and then, a section titled "High Idle, Maximum Torque". In that section is a mention of a "torque spring". I had never seen reference to it before, even in the parts manuals. This is a quote from section 20, page 32. There are also accompanying drawings for illustration.

"High Idle, Maximum Torque:
When a load is applied, decreasing engine speed, the
flyweight force is reduced against the governor
lever. The spring can then pull the lever assembly
and the rack to increase fuel delivery and bring RPM
back up to preset speed.

Additional load would further reduce the flyweight
force permitting the governor spring to pull tension
lever against the TORQUE SPRING, compressing it and
moving the rack to the maximum torque fuel
delivery."

As it turned out, my "torque spring" wasn't adjusted properly. It was one turn off. This limited/restricted the governor arm's travel just enough where it was causing my trouble, which boiled down to very limited ability of the governor to function properly. When the engine didn't have enough "umph" to get the job done on the throttle setting you had it set at (even up to and including rated PTO setting), it would bog down - until YOU reduced the load or added more throttle manually.

This torque spring adjustment is found on the back side of the governor, and appears similar to a little fire hydrant? There's an acorn nut on the end, and a lock nut. They're both threaded on to a threaded hollow shaft containing the "torque spring". Removed the acorn nut, unlocked the lock nut, and because I was totally blind regarding proper adjustment procedure, unscrewed the threaded section one full turn, allowing the throttle arm within the governor to open the injection pump rack a few thousandths further. This totally cured the evil that's been bugging me since buying this tractor months ago. Because this adjustment has "tamper" paint on it to identify the fact anyone's messed with it, and the fact that paint was intact, I have no choice but to believe this adjustment has been screwing with this tractor's performance since new!

It will now mow grass, back blade with the front wheels off the ground, and basically function like every other diesel powered tractor I've ever owned, from about 1600 rpm on up. NO further need to be working with the engine buzzing at full PTO rpm, or even 2500? Now, it's more of a question of what mower blade speed you're after, or the desired speed of your hydraulics when working with the FEL? The engine no longer bogs when loaded, ever, and the guy sitting in the operator's seat has a great big grin on his face! -Al

 

[kuboman]

Re: JD 755 CUT Governor Issues? Final update, problem identified/repaired!

It's been a while since posting last, but wanted to leave this for anyone with a similar problem following this at a later date -

As suspected, it wasn't my imagination, unrealistic expectations, or a diesel engine designed to develop it's power at high rpm only at all. It WAS a governor issue at the root of the evil haunting me.

Still unable to put this issue down, I was going back through the manuals and discovered a section devoted to "Theory of Operation" in the Component Technical Manual (CTM) that I hadn't seen before. There's a section there regarding governor operation, which broke the governor's operation down to the starting and idle phases, and then, a section titled "High Idle, Maximum Torque". In that section is a mention of a "torque spring". I had never seen reference to it before, even in the parts manuals. This is a quote from section 20, page 32. There are also accompanying drawings for illustration.

"High Idle, Maximum Torque:
When a load is applied, decreasing engine speed, the
flyweight force is reduced against the governor
lever. The spring can then pull the lever assembly
and the rack to increase fuel delivery and bring RPM
back up to preset speed.

Additional load would further reduce the flyweight
force permitting the governor spring to pull tension
lever against the TORQUE SPRING, compressing it and
moving the rack to the maximum torque fuel
delivery."

As it turned out, my "torque spring" wasn't adjusted properly. It was one turn off. This limited/restricted the governor arm's travel just enough where it was causing my trouble, which boiled down to very limited ability of the governor to function properly. When the engine didn't have enough "umph" to get the job done on the throttle setting you had it set at (even up to and including rated PTO setting), it would bog down - until YOU reduced the load or added more throttle manually.

This torque spring adjustment is found on the back side of the governor, and appears similar to a little fire hydrant? There's an acorn nut on the end, and a lock nut. They're both threaded on to a threaded hollow shaft containing the "torque spring". Removed the acorn nut, unlocked the lock nut, and because I was totally blind regarding proper adjustment procedure, unscrewed the threaded section one full turn, allowing the throttle arm within the governor to open the injection pump rack a few thousandths further. This totally cured the evil that's been bugging me since buying this tractor months ago. Because this adjustment has "tamper" paint on it to identify the fact anyone's messed with it, and the fact that paint was intact, I have no choice but to believe this adjustment has been screwing with this tractor's performance since new!

It will now mow grass, back blade with the front wheels off the ground, and basically function like every other diesel powered tractor I've ever owned, from about 1600 rpm on up. NO further need to be working with the engine buzzing at full PTO rpm, or even 2500? Now, it's more of a question of what mower blade speed you're after, or the desired speed of your hydraulics when working with the FEL? The engine no longer bogs when loaded, ever, and the guy sitting in the operator's seat has a great big grin on his face! -Al

Is there a chance you could post a pic of the back of your pump? I know of the spring but need to confirm the adjustment. I wasn't aware it was a external adjustment.

 

[michahicks]

Sure, here you go! To help get your bearings as to location, the dipstick handle is easily visible bottom center of pic, fuel filter to left. Also visible is the white "tamper" paint, and the small hole in the acorn nut to allow the use of safety wire? Pay attention to the gaskets on either side of the lock nut, and once the lock nut has been loosened initially, that shaft is free to turn with it, possibly causing you to loose track of the initial setting?

 

[kuboman]

Sure, here you go! To help get your bearings as to location, the dipstick handle is easily visible bottom center of pic, fuel filter to left. Also visible is the white "tamper" paint, and the small hole in the acorn nut to allow the use of safety wire? Pay attention to the gaskets on either side of the lock nut, and once the lock nut has been loosened initially, that shaft is free to turn with it, possibly causing you to loose track of the initial setting?

That's great, thanks a bunch.

 

[kuboman]

Sure, here you go! To help get your bearings as to location, the dipstick handle is easily visible bottom center of pic, fuel filter to left. Also visible is the white "tamper" paint, and the small hole in the acorn nut to allow the use of safety wire? Pay attention to the gaskets on either side of the lock nut, and once the lock nut has been loosened initially, that shaft is free to turn with it, possibly causing you to loose track of the initial setting?

That's great, thanks a bunch.

 

[yankeerider]

Great info. Thanks for the update.

Sent from my iPad using TractorByNet

 

[michahicks]

Upon further thought...

Maybe worth mentioning, I think everyone is familiar with the concept of tuning diesel injector pumps, injectors, etc. or installing "performance chips" for increased power? If you think about what is going on with this adjustment (detailed above), somebody wanting to try something like that with an engine using this governor, might find this adjustment is a good place to try that? You are pretty much setting how far the rack will be opened under max load... which translates directly into how much fuel will be passed to the injectors.

In my case, this adjustment had been set so conservatively it pretty much crippled the tractor's performance. (I have to wonder if others have been set similarly?) Where I set it fixed the issue, but if taken further? Well, I'm not going to find that out.... VERY happy with the way it is!

Last thought. With the availability of both the manuals that cover so much detail regarding this engine/tractor, I find it incredible there's such a big hole when it comes to information related to the governor's function? They discuss it during "performance" checks, but not a word further regarding what to do or where to go if it fails? It isn't like you need anything special to service it either...

-Al

 

[kuboman]

Just an aside here, I have an older JD 4 wheel drive that I replaced the injection pump on. The way it came from the factory made it so the tractor had to be full throttle all the time to get any response from the engine. A small adjustment to the torque capsule completely changed the response of the engine. It gave way more of a performance increase than changing the max fuel setting.

 

[michahicks]

More details, or links to more details?