Urba Centurion Update - (Kubota diesel, 100+ MPG in mixed driving - Fall 2012 on)

[changzuki]

Just wanted to share a recent student digital documentary video with the group.
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It's roughly 11:36 in length.
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Kudos to the those students, the "Awesome threesome" for creating this:
- Alexander Norton
- Chris LaRock
- Eddie Guiracocha
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https://www.youtube.com/watch?v=HQUJxV8QxEQ

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Thank you!!!
~CrazyJerry
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[changzuki]

- Is "close enough" - "good enough"?....
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The new Zexel injection pump arrived.
Externally it was an exact replica of the original D850's Diesel-Kiki pump.
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Since all stock pump shims remained in-tact, and nothing else was disturbed, then this should be a plug-n-play unit except for bleeding the air out of it. So, it was installed and the air bled.
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Following that was the new injectors and they were bled. With the intake bolted on (and a game plan in place just in case it decided to "run-away"), it was time for a little test.
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30 seconds of glow plug cycle later and a twist of the key and the D850 sprung into life! There was a mildly impressive soot bloom out the tailpipes but that was chalked off for now.
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The engine idled exceptionally well and had a very healthy and uniform clack-clack-clack. The vibration previously noted seemed to be gone.
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Clearing the first cycle of the thermostat and no fuel leaks, there wasn't any reason a road test could not be performed, so down with the hood.
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The first test was going up through all six-speeds and checking for smoothness at varying rpms: Very smooth. The next test was from a stop and going through the sixes again, but this time hitting the governor's limit each time. From second gear and up it was in every respect a complete slug! In fact, 4th gear with overdrive engaged (6th) it was not even possible to hit 3000 rpm or break 68 mph even going down a reasonably steep hill! Moreover, climbing the same grade of uphill immediately after,
necessitated downshifting all the way down to second gear, finally settling in at a lackluster 23 mph. No smoke noted.
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After a very leisurely trip back home, it was looking like this part of the project was far from done. I've probably voided the warranty on nearly everything I ever bought within the first month but this pump was about to lose its status on the very same day I received it. For those of you who've also "been there - done that" I salute you!
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Although the Zexel pump is the "exact replacement" called for, internally it's not even close. Among the most stark differences are the delivery valves (which are smaller) and their angles are not as abrupt as the original Diesel-Kiki's.
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To satisfy my curiosity, I did swap out the delivery valves in their entirety but the difference seemed only negligible at best, and there was still the issue of the rpm leveling out way before 3000 rpm. This current rpm max of about 2500 did coincide with the specs on some of the tractors that were originally equipped with this same engine... Hmmmmmm...
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There was one more small detail too:
At light throttle in any gear (but more pronounced in the higher ones) driveability sucked. While driving in first or second, if you've ever moved your accelerator up and down as fast as you can - the bucking you feel as that transmits through the drivetrain is exactly what I was feeling. Woo-hoo - ride'm cowboy! Pressing or releasing the accelerator fore-or-aft that point would result in a steady state. The "Tiny Tach" (transponder around the injector line tach-pickup) provided a clue: The loss of an injector line pulse
resulted in the tach switching over to the clock mode.. Seemed there was now something going on with the pump that wasn't there before..
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And the problem...oh yes....it will be found.....
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~CrazyJerry
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[changzuki]

- A vibration
- A swath of black smoke
- One set of new Injectors
- Followed by another set of new Injectors
- A disintegrating Injection Pump
- Followed by a new Injection Pump
- A bucking Centurion
- No problem...
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https://www.youtube.com/watch?v=2H5uWRjFsGc

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It's going to be another very looooong night......
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~CrazyJerry

[nemo]

The saga continues.

[changzuki]

- A meeting with the Governor....
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At this point, ALL of the immediate issues are traced to the new Injection pump and Injectors but the remedy just may be through the Governor itself. Since the governor is separate from the fuel pump, then one might think it could be dealt with easily and directly - not exactly.
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Removal of the Governor is a major job and is likely unnecessary as long as we use caution and a steady hand. To understand what's going on in relation to the problems, let's look at the governor as it would look outside of the engine:
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It may look simplistic but there's a lot going on when this piece is doing its job. Using the following pic as a reference, let's look at what it does:
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Look at the lime green circle. This is where the Injector Pump's rack dowel pin slides down into. Once you know that, it becomes a bit more clear that as the "arm" holding the green dowel pin moves forward, the fuel rack will increase the pump's output and the engine will rev. If the arm moves rearward, the fuel rack will cut back the fuel delivered to the injectors and the engine will slow down (or stop if it goes rearward far enough).
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When you push down on Centurion's accelerator pedal, you are really only pulling on that arm via a spring. As the engine begins to rev near its 3000 rpm limit, the centrifugal force of the fuel pump's camshaft weights act on the same arm to push it rearward, thus limiting the fuel rack's travel - this way you don't over-rev the engine and blow it to smithereens.
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Notice the yellow arrow in the above pic and see that it's pointing to a slot. That slot is essentially a "tolerance" area between the two arms. If the pulling of the accelerator spring closely matches the pushing force of the fuel pump camshaft weights, then the dowel pin from the closer arm is allowed to "free float" just a little bit (both forward and rearward) in that slot. In certain cases, likely due to both heat and vibration, the accelerator spring can resonate and then you get a bouncing back and forth action between "its pull", and the "camshaft weight's push". When this happens (in this case under a light load in any gear) the fuel rack will move fore-and-aft just enough to give you a rodeo ride (bucking action.) This normally would never happen if this engine was in the stock equipment is was designed for since there would normally be a constant load on it (Ex: A Genset, Tractor, Bobcat, etc..)
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This is actually a pain in the a$$ to fix and did involve a ton of hours to the extent of making new governor springs and relocating them outside of the engine (they are mounted internally from the factory). There is very little room to work with if keeping the springs mounted internally. The pic below shows one of those springs dangling out from the engine, actually from one of the governor arms:
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Here is my attempt and creating larger and smaller diameter springs to straighten this issue out:
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After fiddle-phooking around with this forever, it finally worked really good - very acceptable and very responsive with only the slightest hint of the bucking and only if you're intentionally trying to feel it!
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There was still the lagging issue of 2400 max rpms to deal with but clearly I was in the right place!!!!
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~CrazyJerry
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[changzuki]

- Dealing with the D850's reduced power and missing RPMs...
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Like the new injectors, apparently the "replacement" Zexel injection pump is less of an "exact replacement" and more of a "close approximate match". The current issue is the ~600 rpms that are now missing and thus limiting us to about 2400 on the tach along with reduced power for the hill climbs.
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If the governor is suspect, it's possible to watch it in action. Removing the "speed control plate" (and associated internal springs!) located directly in front of the injection pump will provide a window:
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Making sure your fuel shutoff is still hooked-up, it is possible to start the engine and watch the governor do its job. Although not recommended, if you're really careful, you can reach in physically move the governor forward to increase the rpms. Not only will you feel the governor weights gain strength to return the rack to idle, you will likely be swathed with a geyser of engine oil! Looking at Kubota's timing gear layout explains why they are so effective at slinging oil from the oil pan upward:
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After watching the governor through an OPEC champagne party, it was pretty easy to see what was limiting it and thus causing the fuel rack to stop short:
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Removing the acorn nut style cap screw allows access to the slotted adjustment screw and jam nut.

"Loosening" the adjustment screw will allow a more travel and allow the fuel rack to more fully open.

As long as your accelerator springs can overcome the governor weights, the previous rpm limit will be raised. NOTE** When abruptly accelerating from idle, this extended rack travel may result in a blast of "rolling coal" until the mechanical governor catches up to back off the fuel rack. The governor then regulates the opening of the rack at a more realistic rate and the exhaust should be mostly free of visible soot.
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**NOTE** There is a similar adjustment for the minimum governor travel to stop at and it's located at the lower rear of the injector pump and protrudes from the engine casting (much like the front adjustment does)...
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With adjustment made to obtain roughly 3400 rpm we are now ready to mop up from the Boston Tea Party and go for a road test!
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~CrazyJerry
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[The_Jed]

Amazing stuff. I've really enjoyed reading about your car!

[pgfpro]

Me too!!

Very informative write up!!!

[ME_Andy]

OPEC champagne party, LOL. Fewer champagne parties at OPEC these days...

[changzuki]

The_Jed, pgfpro,
Many thanks for following and commenting on this thread. The entire project has gone way beyond what the original intention was - just another piece of the off-grid experiment - so I figured may as well document it right?

ME_Andy - I laughed to when the description of that oil deluge just kinda rolled off the keyboard. It easily took an hour to clean everything up afterward.

You folks have a safe and happy holiday!!

~CrazyJerry