360 motor in 1972 Dodge Demon vibrating

[Cubzy]

Hi All,

I recently purchased a 1972 Demon with a 360. It has 340 X Code heads, 0.474 lift cam, Edelbrock intake and not sure about the rest. Car starts well and runs well.

I'm unsure of the vibration the motor transfers to the car. When stopped you can see the hood in front of your vibrating, bucket seats vibrating, door panels etc. A lot of the screws in the car have vibrated out. Should I be concerned with this? I thought maybe motor mount was suspect. The motor appears to be firing well and not misfiring. I talked to someone today saying that 360's are externally balanced on the front of the engine that the pulley is mounted on. Perhaps it doesn't have the correct balancer on it? How can I tell if it has proper balancer? I would like to know what your thoughts are or corrective action???

Thanks in advance.

 

[Moparman1806]

Could possibly have the wrong balancer, flex plate/ converter, especially if it used to be an internally balanced 340. It doesn't have solid motor mounts?

 

[Cubzy]

Could possibly have the wrong balancer, flex plate/ converter, especially if it used to be an internally balanced 340. It doesn't have solid motor mounts?

Motor mounts appears to be a little rubber sandwiched between metal plates.

 

[Moparman1806]

It this an auto or stick? Did previous owner have engine built? If so, maybe you could find out if they had any engine rotating parts balanced or not. An externally balanced 360 will have a counterweight on the outer ring of the balancer. Internally balanced motors have no counterweight. In the picture, the lower one is externally balanced.

 

[Dartswinger70]

I had a pressure plate that was defective and or threw a weight on my 340 that caused a hell of a vibration sitting still in neutral. When I revved it up it was terrible.

 

[DustyRoads]

Is it an automatic? Like MoparMan1806 said, the torque converter is different for a 360, too. It has a large balance weight welded on. You can use a regular 904/727 torque converter, but only if you buy a weight and weld it on. Or, you can buy a special flex plate from B&M that looks like a metal frisbee with a semi-circular "bite" taken out of one edge. The bite accomplishes the same thing that a balance weight on the converter housing would. Both things (harmonic balancer +weighted torque converter or harmonic balancer + special flex plate) are needed for an automatic with a 360. If it's a manual...I don't know. But it wouldn't surprise me if something weird had to be done to the flywheel to make it work with an externally balanced engine like the 360.

 

[moper]

If there was a mechanical imbalance it would be felt all the time the engine is running, and if revved in nuetral or park it gets worse. around 4K you'd be panicing, not losing screws. I would suggest some basic engine diagnostics in addition to looking at the flexplate, convertor, and harmonic balancer. A simple compression test will show a bad valve or weak cylinder that could be causing a milder shake that smoothes out at times.

 

[Dartswinger70]

If there was a mechanical imbalance it would be felt all the time the engine is running, and if revved in nuetral or park it gets worse. around 4K you'd be panicing, not losing screws. I would suggest some basic engine diagnostics in addition to looking at the flexplate, convertor, and harmonic balancer. A simple compression test will show a bad valve or weak cylinder that could be causing a milder shake that smoothes out at times.

there is some truth to the "panicing" you mention, I had my Dart in the shop dignosing my bad pressure plate, when I revved it up , the people standing around my car took a few steps back, they didn't know what was going to happen next it was like they were expecting pieces to fly, or maybe an explosion LOL!