[changzuki]

- Is "close enough" - "good enough"?....
.
The new Zexel injection pump arrived.
Externally it was an exact replica of the original D850's Diesel-Kiki pump.
.
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.
.

.
.
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.
.
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.
.
The engine idled exceptionally well and had a very healthy and uniform clack-clack-clack. The vibration previously noted seemed to be gone.
.
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.
.
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.
.
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!
.
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.
.

.

.
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...
.
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..
.

.
.
And the problem...oh yes....it will be found.....
.
~CrazyJerry
.