bad vibration

[rod1234]

I have a bad vibration on a 66 Tbird I just purchased. I put it in the shop and they found a flywheel that had been drilled 4 holes side by side. They changed out the trans mount and the torque converter. I have motor mounts on order but mine look ok. The vibrartion is present at idle or while driving. The vibration seems to be around 2500 rpm worst case. 390 with a c6
Any ideas of what else could be causing this problem. Engine balance on front of eng is rock solid steady.
Thanks Rod

[olddog]

I think all FE block Fords were externally ballanced engines. That means that the harmonic ballancer and the flywheel are out of ballance in order to finish ballancing the crankshaft. The holes drilled in the flywheel may be a poor attempt to ballance the engine by a person with enough knowledge to be dangerous.

Since you likely have no idea what rods and pistons are in this engine or what may have been done to the crank, you are going to need expert help from a good machine shop that knows how to ballance a crank. I'm not sure if they can ballance it in the car, but that is where I would start.

[olddog]

I looked this up in a book tittled "How to Build Max Performance Ford V-8s On a Budget" by George Reid. According to the author, some FE engines were internal and some were externally ballanced. The 410 and 428 were externally ballanced the rest were internally ballanced. So a 390 should be internally ballanced. However he claims the FT engines (which I gather is FE engines put in trucks) are all externally ballanced, and the parts can be interchanged between FE and FT engines.

So again we come back to, do you know what has been done to this engine on its last build? People sometimes use aftermarket rods and pistons with different wieghts and don't have the crank reballanced. Also there were a lot of FE engines and all the parts can be mixed. For instance your block may be a 390, but someone could have dropped a 428 crank into that block to stroke it out to 410, in which case the crank is externally ballanced.

My first approach would be to replace the flywheel that has had holes drilled in it, with the correct one for a FE 390. You could replace the harmonic ballancer with the correct one, too. If that doesn't solve the vibration, you need help.

Note: the book mentioned above has some dead wrong information in it. Things that a person writting books should understand. So I am not certain that the information in this book is correct.

Does anyone know who this George Reid fellow is? He made some whopper mystakes. I wouldn't let him build an engine for me, if he offered to do it for free.

[justen]

Is the engine on a automatic? Could be the torque converter causing the vibration. If it's manual a flywheel and harmonic balancer are about the only thing you can look at with out pulling the engine. Some people mistake a mis-fire for a out of balanced engine.