Chrysler Repair: Engine shakes violently, chrysler sebring convertible, intake manifold gasket

Question
I have a 98 chrysler sebring convertible JXI that shakes violently during startup.  It is a 2.5L engine and has 6 cylinder.  Before the engine runs, there is a second of hissing sound and then the engine starts running and shakes violently.  This happens right after I did a change on distributor core.  When pulling the distributor rotor, I accidentally nick the plastic a bit like .5 mm notch.  Will this cause imbalance on the rotation?  Also when puttin the distributor, to adjust the rotor back to the old position, I rotate it clockwise (later I read that the engine rotate counterclockwise, but the distributor gave no resistance to me).  I also notice that there is oil leaks from engine gasket to the spark plug so I clean the cables.  I was not able to open the engine to change the gasket. (have tried hammering it with rubber mallet after removing the bolts, but still is not opening up).  Any advice of the reason for the engine shakes is trully appreciated.  Thank you for your time


Answer
Hello Andreas,
I don't think that knicking the rotor plastic will cause an imbalance, but look at the damaged area to see if it might allow some current to arc to ground at that spot which would cause a misfiring of the ignition. The violent shaking usually is due to one or more cylinders not firing properly or at all. But you didn't say this continues after warm-up so it must be a temporary problem just after starting? If so, then I wonder if the hissing at start up might be involved? Perhaps you have a leak around the intake manifold gasket which then disappears as the parts that mate together heat up and close off the leak? Oil around a spark plug too due to the gasket leak could cause a temporary misfiring as well. I know that it is a job to work with the rear intake manifold or to get to the spark plugs on the rear bank, but if the hissing is coming from that area that may be necessary.
Violent shaking could also be exacerbated by a weak engine mounting. If the engine is too loose due to that, then a misfire will cause the engine to really oscillate more than otherwise. So check the three engine mounts to see if any appear to be excessively flexible.
I wouldn't be concerned about the apparent rotation of the distributor rotor because it has a helical gear so when you push it back down into place it will cause the rotor to move that way. As long as the rotor ended up in the same position it was before you took the distributor out, that should be o.k.
I can send you the steps involved in servicing the rear cylinder intake manifold if you want to give that a try.
Roland