Re: Timing Question.

Posted by jdemaris on December 30, 2008 at 14:20:03 from (72.171.0.140):

In Reply to: Timing Question. posted by Guido on December 30, 2008 at 05:40:01:

I think with some of these posts, we are getting lost in technical semantics. In the apical/original post, Guido posed a question that is so vague, it cannot be accurately answered. He did not ask "what is the standard reference frame used for valve or ignition timing." If he had, it would make a little more sense. I'm not even sure what timing is in question. Time of ignition? Time of diesel fuel injection? Time of diesel combustion? Time of valve opening in relation to the piston it affects? Time of valve opening as it relates to the flywheel position? Maybe "time to buy a new engine?"

To be technical, a four cylinder engine is basically - four little internal combustion engines all tied together. Each one of those cylinders, individually, can be affected by piston travel as it relates to valve opening, valve closing, time of spark or fuel injection, etc. All of those things can happen differently for each cylinder - and the crankshaft-end will not always work as a common reference point for all. Yes, it IS designed to do so in most cases, but things do NOT always work that way. Measuring each crank throw will work, but that's not usually practical.

I can name a few examples. Bent connecting rods, one throw of a crank a little off, bad cam lobes, looses rocker arms causing late valve timing, tight rocker arms causing early valve timing an in-line injection pump with uneven injection rates, diesel fuel injectors cracking at different pressures that changes firing timing, etc. Note that not all tech manuals for all engines refer to piston position, or time of ignition in reference to the crankshaft-end-marker. They DO often use the crankshaft or flywheel as a marker of general piston position.

Not long ago I had to fix a Deere diesel that had every cylinder getting injection at the proper time when using the crankshaft marks as a rerference. But, one cylinder skipped and smoked worst than the rest. Found out later one piston was not where it was supposed to be - it was late and low. That's one example where a crank-end reference for a muliple cylinder engine does not always work.

Well, now I guess I'm the one wasting a lot of digital hot-air on a question that has no technical meaning anyway.

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