If you feel the vibration when standing still, you might suspect the harmonic balancer. The arrow in this photo from rockauto.com points to the gel insert than can let go. If the outer cast ring rotates on the hub, and it has an extra offset weight, it will cause a vibration. Many engines are "externally balanced" and need that extra weight on the balancer and torque converter. Auto parts stores have large catalogs full of replacement balancers.

Answered by caradiodoc (expert)
17,655 answers provided

The engine had also developed an oil leak on the back end of the intake manifold so I got it removed and noticed oil in the intake runners and the intake ports. The left side intake gasket fell off when I lifted the manifold off. The right side didn't take much to get it off either. Back to the balancer. I purchased a new one from the local parts store. I compared the two and noticed that, just like in your picture there's a timing mark, nearly in line with the keyway groove on the new one. On the old one, if the keyway is the 12 o'clock position, the timing mark is more like about 10 o'clock. To me that kind of points toward the balancer. Forgive my going on but after removing the intake manifold i verified that the balance shaft still turns. The crankshaft can be rotated back and forth about 1/4" or so before it moves. I'm guessing that's 227K miles of wear on the timing chain. If you have any thoughts or ideas, I'd be interested in hearing them. Thank you for your time.

Response from jerrylmo
7 questions asked

Don't read anything into the location of the key way. What you're looking for is evidence that the cast outer ring turned or is moving off the hub. If the timing marks are different between the two, that would appear to be the problem.

Answered by caradiodoc (expert)
17,655 answers provided

The more I see the more it looks like the balancer is the culprit. That being the case, since I'm going to remove the balancer can the oil seal for the balancer be replaced without a lot of grief? Thanks, Jerry

Response from jerrylmo
7 questions asked

Drill a small hole in the metal part of the seal, then run a long thin self-tapping screw into it. You might have to use two screws directly across from each other. Once they bottom out on the crankshaft journal, they will pull the seal out.

You can also reach into the hole with a cotter pin pick to pry the seal out. That's a fat pick with the end bent at a 90 degree angle.

Answered by caradiodoc (expert)
17,655 answers provided