Re: engine balance

Posted by Tim Cole On 2013/3/24 9:41:11

Okay,

There are two types of motor balance. Internal and External.

An internally balanced motor is done the obvious way in that the crank and rods are balanced.

An externally balanced motor uses the flywheel to offset imbalance of the internal motor parts. Most V-8's are externally balanced meaning that the flywheel is matched to the crankshaft as a set. In those motors as long as the pistons and rods match the old stuff then everything will be fine.

Packard did not authorize rebabbiting rods and sold replacement rods according to casting numbers. They also authorized rod replacement with insert bearings which indicates that senior motors were externally balanced.

Proof would come from swapping a flywheel. If the motor then vibrates then it was externally balanced.

So..... if the rods are original and the pistons weigh the same as the old ones then you are probably okay. However, if your vibration damper is junk you won't know that unless you have the motor balanced which is a lot easier than putting it together and not knowing where the vibration is coming from. So balancing does pay, especiallly if you are doing a Packard 12 with a rotten damper.

Now what does an imbalanced motor feel like? Raise the RPM to around 2500 and you will feel vibration through the steering wheel. It will feel like you have a weak cylinder.