Quote:
Originally Posted by DWC
I've been reading various vibration threads and I'm wondering if the vibration is a result of a physical imbalance (i.e.- internal rotating assembly out of balance, flywheel counterweight incorrect) or an imbalance related to tuning (i.e.- misfire, incorrect timing, etc)?
Wouldn't a physical imbalance begin to vibrate at a certain RPM and continue to increase in severity through the RPM range? Not always. I regularly see an engine with a hard miss at idle and when you rev it up it will start to go away. Not because its no longer misfiring, but because the speed the crank is moving makes it become less noticeable that that cylinder isn't producing power
In an effort to be concise, I'm going throw out some facts from what I know at this point:
-Engine DOES have run-on/dieseling when I shut off the ignition. Usually around 3 seconds of continued rough idle before finally dying.
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Seems you might have answered your own question. I also added to part of it about vibration getting worse.
Also since you've eliminated the drive line from the problem lets take a look at other rotating parts that I've seen cause vibration. The balancer, easy to check by setting cylinder 1 at TDC and seeing if the timing mark lines up with zero on the timing tab. Balancers have been known to slip and will cause the type of vibration you're having. Ironically your timing might be "correct" with the timing light, but if your balancer slipped its off in the engine causing your dieseling.
The accessory drive is another one. If you're using a cheap drive that things can flex around that can also cause a vibration. Free reving an engine doesn't always work, sometimes it needs a load on it like when driving. Misfires are the most common that need a load to show up. At this point I would get your timing corrected and go from there. If you have a GoPro you should mount it under the hood so you can watch the engine and see what its doing when the vibration happens.