Engine out of balance

[chances80AMX]

Hello, I have an 80 amx that I just intalled a 304 in it. It is using the straight six flywheel. The engine has a lot of vibration. The motor was purchased by autozone (crate). Could it be that the motor is not balanced or am I using the incorrect flywheel?

Thanks for any help!

[Big Bad AMX]

AMC engines are externally balanced, so each AMC motor (crank, rods and pistons as a reciprocating mass) was originally match balanced to the flywheel or flexplate on the back of the motor at that time. Which means each flywheel or flexplate only matched the original crank, rods and pistons. It was spun up with holes and depressions drilled in that flywheel or flexplate to get that precise balance (just like a rim and tire are spun up as a unit). So, you can not take a flywheel off of one AMC motor and put it on another motor.

Autozone should have given you a flywheel that was balanced to that rebuilt motor. Unfortunately, you'll need to pull the engine and take the crank, rods and pistons and flywheel to a balance shop and have it match balanced as a rotating mass.



.

[cali201]

that does not sound like fun!!!!!!!!!!!!!!!

[blurat]

Hi, AMC are balanced like posted by bb. However, there is no way a six cylinder fly will be even CLOSE to balance as a V8. You might try to get a 304 flywheel and that would smooth it out a lot, probably plenty. I would do that before teatring my motor apart. If you ever do tear it down the best thing you can do to any engine is have it balanced.
b

[donsjave]

Hi, AMC are balanced like posted by bb. However, there is no way a six cylinder fly will be even CLOSE to balance as a V8. You might try to get a 304 flywheel and that would smooth it out a lot, probably plenty. I would do that before teatring my motor apart. If you ever do tear it down the best thing you can do to any engine is have it balanced.
b

I have found though out the years when you purchase a motor, it must come with the flywheel. AMC motors require a balance motor to start and the only way that AMC did their motors was by the way that bb described it. Even when you change flywheels between V-8s the balancing must be done so that you do not shake the motor apart. The lack of balancing will cause forces that are very hard on the rod bearings, the crank bearings, and other damage that can cause exteme wear on the internals of the motor. The motor will not last long and along with an imbalanced motor comes drivability problems. I would highly recommend that the entire assembly be balanced as outlined by bb. I would also yell my fool head off at Autozone for delivering an unbalanced motor. It's kind of like delivering a half of motor, Nice to look at but you can't do anything to it including starting it.