I recently swapped transmissions from an auto to manual with my 351C engine. I couldn't find a 351C flywheel, so I used one that came off a 300cid inline six. After engine start-up I had some noticeable vibrations at just above idle and then the vibrations seemed to smooth out some when reaching around 2400 rpm and better, but there still seemed to be a little vibration left. At idle rpm the vibrations were not noticeable. Please Help with the following questions.

1.) Are the 351C engines internally or externally ballanced?
2.) Do I need to change-out the harmonic ballancer, and with which one?
3.) Will it harm the engine if I run it with the vibrations?

 

Yes, you need a flywheel with the 28oz imbalance. 300's are internally balanced. The good news is that it should be rather easy to find one. 289's, early 302's, early 351W's, 351M, 400.

Should you change to a balanced flywheel? Yes. You'll beat your main bearings up pretty quickly.

The stock harmonic balancer should have been fine.

 

Thank's Much pcmenten for the information concerning my problem!