Re: Diesel opacity tests for road vehicles

Posted by jdemaris on September 23, 2006 at 19:43:56 from (66.218.12.162):

In Reply to: Re: Diesel opacity tests for road vehicles posted by Bob on September 23, 2006 at 17:22:25:

The screw absolutey effects more than full-throttle operation. It's a "maxiumum fuel" screw because it does determine the maximum fuel volume that can be pumped, but any adjustment to it effects, to a lesser degree, fuel delivery throughout the entire range of operation - especially in a pump with some degree of metal-parts wear. I've seen it happen many times when I've had a pump on a test-stand checking volumetric output at various RPMs.
In regard to other factors you mentioned that affect visible smoke, starting, running, etc. well, yeah - just like just about any diesel. But - I've pulled a few 6.2s apart with very sloppy timing chains and they had been running perfect as long as the fuel timing was kept right. In fact - the Suburban that my son now has - blew up a few months ago with 520,000 miles on and it ran like new - until the engine siezed with the crankshaft now in three pieces. I'm not sure what happened - it went with no warning - some claim the cranks break due to metal fatique, others claim the main-journal webs break first. Guess I'll never know, but I've got two main-journal webs tore clean out of the block with the bolts still intact. That's how my son wound up with the Suburban. I had a spare engine - and told him he could have it if he wanted to do the work. So, he came here for his vacation and put the engine in.
Again - about the timing chain - from what I've experienced, it has very little effect on running other than retarding the timing of the injection pump - which is easily worked around by bumping up the static timing a bit.
In regard to issues, e.g. timing. That's always a factor with mechanical injection. Sometimes brand-new engines have to be timed a few degrees out of spec. to run right - since factory settings are average settings and not custom tailored to the individual engine. Older U.S engines were built with wide-tolerances and therefore varied from one to another. Now, the static timing is one thing -which can change over time just by gear-train wear. But, the automatic timing advance in the pump tends to get weak at less miles since it depends on low-fuel pressure with the proper variation in low-fuel pressure in accordance with RPMs and various rubber seals to operate properly, via the transfer-vane pump built into the back of the injection pump. I've come across many engines that had just about no working advance at all - and that will cause smoke, cold sputtering, etc. On farm tractors it's easy to check with the engine running by using a plastic timing window. On the 6.2s though, often a pulse-adapter used through a timing light is needed, unless you've got some sort of flame-sensor to go into a glow-plug hole.
As far as crankcase oil getting burned - it used to be a common problem in diesels that used air-chokes for engine shutoffs - e.g. Mercedes. Detroit Diesel also has it - but only for the emergency shut-off. The reality is - if the engine is using substantial engine oil in the combustion chamber - you're going to notice pretty soon when your dipstick reads low.
And injectors? I'm going to have to go by my own experience. I've pulled apart some good clean running diesels and, after testing the injectors, found them to be in horrible shape. By horrible - I mean just about no atomization, but they were not plugged either - fuel just dribbled out. So, my impression (or inductive reasoning) is - I don't believe that have much affect unless they are REALLY bad. Injector opening pressure, does to a small degree affect injection timing - so when injectors get old, and opening pressure settles and drops off a bit, the timing changes a bit.

Replies:

• There's no use... Bob 20:05:51 09/23/06 (1)
  • Re: There's no use... jdemaris 20:39:34 09/23/06 (0)

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