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?

 

[DrBill]

More details, or links to more details?

Hi there,,, I know this post has sat for a while but it's going to come back up because I'm dealing with the same issue on my 755 and I have the same tenacity as the original poster to solve my governor pains..

I've spent the last two years, ( I travel a lot) remanufacturing my engine and radiator to fight and stop an overheating problem. During this time I've enjoyed a governor that was anything but...

I have all the books and technical data that like mentioned,, explain why all design engineers I've worked with have unpaid bills and cars that won't run... All of them..

At my time of rebuild,,, I cleaned and assembled the governor assembly without changing existing settings,, except I did back out the throttle stop screw so I could be my own governor..

I'm going to review this post carefully, and will be adding my comments and questions..

The 755 is a good chassis,, fun to operate, but the engine is too small for its potential as a tractor and has a 500 rpm powerband.. It for sure needs a sensitive governor..I'm going to have one.. Thanks for this thread...

 

[DrBill]

The adjustment explained toward the bottom of page 3 of this post topic by michahicks is correct, as well as his other comments about lack of information available.

Anyone with a Deere/Yanmar that appears to have low response to load should read the information..

It appears the information will hold true for most of the yanmars used by deere, for sure any TN series..

I hope this post will lay around for someone else to find later, as I'm sure someone will be wanting to know..

 

[Fred Sanford]

I'm having the problem and taking the advise here I removed the cap nut--1/2 off in pic.

I see a small bolt/threaded rod/shaft with 2 nuts on it.

It seems to move freely in that larger threaded piece. I didn't dare turn it but it does seem to pull out a bit and feels loose.
I'm confused as to what to do now.
Do I:
1. loosen the remaining large nut and turn the large threaded piece itself out one turn then lock that nut back and put the cap nut on while leaving the little rod and nuts alone?
2. loosen and back off the little nuts on that rod one turn?
I'd greatly appreciate replies from someone who's done this. Thanks!

 

[DrBill]

Fred,,,,, do not mess with the small nuts connected to the little rod... Leave that alone,,, and yes the little rod does move about,,cand all of that is ok......

The process is like you said in choice 1,,,,,, loosen the big nut and turn the threaded "cylinder" (for no better word), out about 3/4 to one turn,,, then tighten the big lock nut,,, and put the outer cup back on...

The end result of this is the governor should kick in faster and also allow the pump to deliver more fuel..

You can tell if it worked right away with more power and overall behavior..

Let me know how it goes
B

 

[DrBill]

I just now looked at the photos posted by Fred.. The big threaded piece shown in his photo is definitely screwed in too far. Based on what I'm seeing I think i would suggest maybe turning the big threaded piece out maybe 1 and 1/2 turns or possibly more.

It will be ok to trial and error this adjustment.. Back out and try,, then if needed or desired, back out some more.. If you get too much smoke at full power and start chocking out with too much fuel,, you know you went too far, and screw it back in some !

Because of work, I'm not near my tractor, but when I get home next week, I'll do an exposed thread count to see how far mine is backed out..

 

[Fred Sanford]

Dr. Bill,

Thanks a bunch for the quick response. If it's not raining tomorrow AM I'm going to turn the cylinder out 1 turn and see how that does--if you have an opportunity to check how many threads are exposed on yours I'd appreciate it but I don't want to inconvenience you as I can play with it a bit. I was just scared of messing up something delicate and important. This is the first diesel I've owned/worked on.

 

[DrBill]

Fred, On the topic of this being your first diesel, it can be tricky to adjust your thinking to the different quirks the diesel can have. There are thousands of posts here about the importance of clean fuel and unclogged filters and lines. Keep that in mind while working on your tractor, especially if nothing you do or adjust creates a positive change.

On your yanmar, remember it's running wide open from an air intake point of view all the time. Make sure your air filter is good, and that's about all you can do for air.

The only thing that controls rpm or power is the amount of fuel delivery. When you work on your tractor the first thing to check is free rpm. This means when warmed up for a bit, push the throttle wide open with no load.

If it's a something 55 tractor, The rpm should max out around 3200 to 3600 max. There is a separate adjustment for that if needed and I won't go into that now, but it has nothing to do with the governor adjustment we are talking about here. But, it is important to know about because if you don't have enough free rpm, that would need to be considered first.

Now, the governor adjustment will not affect maximum rpm. What the adjustment will do is allow the amount of fuel necessary for the engine to try and maintain the rpm you have the throttle set to for whatever job you are doing.

Also, keep in mind that your diesel will have a narrow power band compared to gas engines. If your yanmar is a 55 series, this range for making useable power will 2200 rpm plus. For mowing, throttle up to 3200..

Good luck with everything..
B

 

[Fred Sanford]

Dr. Bill,

Thanks for all the help. I caught a few minutes this AM as it began misting and turned the barrel out 1 to 1-1/8 turns. I'd driven it down the road to pull a neighbor out a snowy ditch a few weeks back and it'd bog down going up hills and I'd throttle up and as I topped the hill and started down the other side it'd sound like it was going to run away. Today with the loader on for weight I put it at 3/4 throttle, full forward on the hydro in high range, and set the cruise control. Headed up the hill with almost no change in engine noise (no bogging, it really didn't act like it had encountered a load at all--no smoke or sound like it was working hard either). I also couldn't see where travel speed slowed any either. It might well be fixed--I'll need a bit more time in good weather with it and some real loads to test further. If real work causes it to bog I might unscrew it 1/4 more of a turn and try that.

Now if only we had that quick of a fix for the paint coming off in sheets. Well, that'll be a rattle can for me as it comes off I guess.

P.S. This is the first diesel I've owned and had to work on, I've operated a lot of diesel equipment before. But, I'm also not a diesel mechanic and thus my hesitation to get into a supposedly non-maintenance item like the governor. Before I started searching the web for answers I'd drained the fuel tank--it was clean except for the fuel inlet screen and several inches of pickup line which was disconnected and laying at the bottom of tank (no wonder it ran out of fuel with the gauge reading 1/4 full )--now it's installed and clean. I replaced the fuel filter, bled the system at filter then the injector pump, replaced the first stage air filter cartridge--the second stage looks mint, and the inlet hose was clear. The tach is broke and I don't intend to fix it.

 

[DrBill]

Fred,, glad to hear you got a chance to adjust some. It probably did help. I've had some PMs and emails on this subject several times over the years. About 7 out of 10 times it worked. The times it didn't were bad fuel lines and fuel in general. When I started on mine, my tank and pickups were so bad the screws broke off just trying to get the pickup lines out. I got so frustrated I bought new tank and all related parts, and that was before I knew if the tractor was actually any good or not !

In spite of our good exchange, I actually don't hang out here much. However, I do get an email anytime someone responds to this thread. I did so in case someone else needed info. I hope for sure that yours is another case where it helped..

PS,,, your tach problem is almost always a cable and fairly cheap and easy to replace.
Best Luck,
B

 

[Fred Sanford]

Thanks, it was so nice to find this thread and see other folks had the same problem. I really appreciate your replies. Hopefully my pics and your comments will further help the next person who has this problem.

For the next readers who find this thread: Dr. Bill is right that you need to check fuel system top to bottom before assuming it's the governor. They are strange beasts when they get air in the system. I know my tractor started loosing power on a slight hill shortly after I got it. After a bit trying to figure out what was going wrong I started to suspect it was low on diesel and the gauge was wrong. I added a couple gallons to the tank and bled the system. It would then start but it still did not have enough power to even drive. After sitting a couple hours while I thought things over I looked and 1/2 the fuel filter was full of air. I bled again and it was fine. With an electric fuel pump between the tank and bleed screws if it starts sucking air it apparently churns it into such a froth it takes awhile to settle out and come to the top so it can be fully bled--or so it was for me. I also found it sprays diesel everywhere when bleeding. What a mess and dead grass too. Plus if your tractor has diesel in the tank and is still getting air in the lines--remember my intake screen and the hose that connects it to the pipe leading out the tank had come loose and was just laying in the bottom of the tank thus the effective intake was several inches above the bottom of the tank--your might have too--my gauge was correct. I found this out later as I was checking everything before pursuing the governor adjustment. I took the hood off then the sender unit off the tank, siphoned out all the diesel and inspected inside with a flashlight.

PS I hate to get the thread off topic here for future readers but I'm betting it's the tach itself as the needle spins in circles constantly when running. I'm assuming the tach cable is spinning or it wouldn't do anything. Not going to worry about it now.