F550maranello2

Hi Guys,

I have a 1959 impala I have a LT1 in along with a 4l60e. Issue iv been having is vibration when i rev the engine. To me it feels like a unbalanced flywheel. I installed a brand new (with weight) one and same exact thing. What im not sure about is this engine ( pulled from a 6 speed car) should be externally balanced so I should have some sort of a weight on the flywheel? The flywheel I installed is from autozone reason I ask is because iv seen ones with now weights at all.

As a side note I removed the torque converter and started the engine with out it and it felt a lot smoother, so I replaced the converter with new one and vibration is back..

Injuneer

When an LT1 engine left the factory, manual or auto trans, the engine was externally balanced using a weight on the flywheel/flex plate.

F550maranello2

yea thats what i figured too. This vibration is really strange I know i have the front balancer aligned correctly ( and i made sure of it, left engine at tdc and aligned the marks to noon)

Im gonna try to unhook the exhaust next, im hoping that one of the brackets is welded to the frame by accident and is causing this..

Injuneer

Front unit is a neutral balanced damper, not a balancer. That's why GM didn't key it to the crank.

Chimera96

Op

if you are sure the donor motor is stock vs rebuilt as an "internal" balanced motor than a replacement flexplate/fw for a stock LT1 will work as long as it is lined up on the crank (dowel pin). If your donor motor was rebuilt as a internal balanced motor you need a neutral aka "zero" balanced flexplate/fw. You can buy them or have a stock one neutral balanced at a machine shop for around $50

you mentioned the exhaust may be welded to frame...that would be a grounding issue that would transmit vibrations

F550maranello2

Hi,
This motor is bone stock, the flexplate is new and the dowel pin is aligned. I know from previous mistakes that if the exhaust is welded to the frame it make a ton of weird noises happen. I didnt do the exhaust the previous owner did..