Worked on motor, now have vibration...

[MJ]

Well, I did not think this would happen to me...

I pulled the motor/trans from my 72 911T to replace a broken throw out bearing. While I was at it, I replaced the clutch disk, rebuilt the throttle bodies (Eurometrix),replaced the muffler with a Bursch and installed new "sport" motor mounts. Seemed easy enough so far so I adjusted the valves, set the dwell and timing according to my Haynes manual and started it up. Sounded pretty good so I mulled over the adjustment of the fuel injection pump and clicked it down a couple of notches to lean it out. The car revs good and does not miss or backfire. My problem is that at about 2500-4500 rpm there is a vibration that can be felt through the seats of the car.

My question is this: Are vibrations common and muffled by the stock motor mounts and now with the sport models I am going to feel it or is it something I should be concerned with like my clutch/flywheel out of balance? Is it possible that something else is bent or out of balance by what I have done? Any ideas or suggestions would be much appreciated before I run to the shop. Thanks,
Marty

[Don in Redondo]

Hi Marty, double check your motor and transmission mounts, make sure that the large cup washers/flanges are in the correct positions.......and for good measure you can add an addition 1/8" neoprene spacer between the cup washer/flanges and the rubber buffer in order to take up any compression that has occured to the rubber buffer due to aging. I have seen more vibration problems and chattering caused by loose motor/transmission mounts than any other source.