FireDemonSiC

Alright guys. It seems that what I thought prior about the damper on an external balance engine may not be quite correct. So I want you guys to educate me.

When I built my motor, I took the entire rotating assembly along with the flexplate and damper to the machine shop to be precision balanced. Being an external balance kit, I wanted the best I could get. The flexplate included with the kit was a flimsy stock style, so I instead bought a chromoly SFI flexplate. I did drop the ball a tad bit however by using the damper that was included with the kit. It was a typical 8" heavy, elastomer style damper. I can even tell you exactly which damper it was. Part # PB1050N.

Fast forward 2 years and I'm thinking of slapping a better damper on the engine such as a fluid damper to better control harmonics plus the added benefit of not having to worry about the elastomer failing and shedding the outer ring from the hub. Shaving a few pounds of rotating weight as well is always a plus. Now, bear with me because here is where my question comes into play.

I initially thought that an external balance damper such as with my motor, or any production 400 was precision balanced to that specific rotating assembly. However, after doing some reading I'm now starting to get the jist that it's it's more of a standard incorporated into the final balance. Both the FluidDamper and ATI SuperDamper are both marked as, "External - 26oz imbalance".

I specifically remember that the only modification the machine shop did to my current damper was a small mark made with a drill. Couldn't have been more than ounce or two at best.

My question is, how exactly does the damper on an external balance engine come into play? Is it specifically balanced as a part of that specific rotating assembly, or is it a set standard that is externally added to the balance of the crank vs using larger counterweights?

I just want to make sure that by changing my damper, I will not be eating up my main bearings within the next few thousand miles.

Thanks in advance.

NoEmissions84TA

iTrader: (1)

The first step in understanding balancing is to understand how a crankshaft is balanced and what the purpose of the counterweights are. The counterweights are designed to offset the weight of the rod and pistons. In the animation below, the weight of the counterweight on the crankshaft is represented by the red arrow. The blue arrows represent the weight of the pistons and rods. As you can see, at any point in the assembly's rotation, the sum of all of the forces (arrows) are roughly equal to zero.


If the counterweights are the correct weight to offset the weight of the rods and pistons, the crankshaft is balanced. If the counterweights are too heavy, material must be removed by drilling or milling the counterweights. If the counterweights are too light, weight must be added to the counterweights. This is usually done by drilling a hole in the counterweight and filling the hole with "heavy metal" or "mallory". This filler metal is denser and heaver than steel (but not stonger) so the weight of the counterweight will increase as a result.


When the counterweights alone can be made to balance the crankshaft, the crank is said to be "internally balanced". If the counterweights are too light by themselves to balance the crankshaft and more weight is needed, an "external balance" can be used. This involves a harmonic dampener or flywheel that has a weight on it in the same position as the counterweight that effectively "adds" to the weight of the counterweight on the crankshaft.Since the harmonic dampener (front) or flywheel (rear) play a part in the balancing of the assembly, they must be installed on the crankshaft when it is balanced. This is unlike an internal balance configuration where the harmonic dampener or flywheel do not contribute to the balance of the crankshaft and are not required to be installed when the crankshaft if balanced. Both methods are used from the manufacturer. An example of some factory internally balanced engines are Chevy 305 and 350 (2 piece rear seal only!), Chevy 396/427, GM LS-series, and Ford "modular" 4.6. Some examples of factory externally balanced engines are Chevy 400 and 454, Ford 302 and 351W. Some engines are even a combination of both: being internally balanced in the front and externally balanced in the rear! The most common example of this is the Chevy 350 (1 piece rear seal) including LT1. Regardless of how an engine is balanced from the factory any balancing method is acceptable as long as the required harmonic dampener and/or flywheel is available.

Your balancer is a PowerBond. In your case, the machine shop did to my current damper was a small mark made with a drill. Couldn't have been more than ounce or two at best., you cannot just replace your balancer with another because it has become "custom". If they did the balancing without ever touching it, then you could replace it with any other balancer with the same amount of imbalance.

AlkyIROC

The hole they drilled in you dampener couldn't have removed an ounce or 2. More likely, they removed grams.

You have 2 options.

1: Install a new dampener and hope the few grams it may be different won't greatly affect the engine balance.

2: Tear the engine down and take the whole rotating assembly in for a rebalance.

How far out can it be out of balance? A factory engine is far from being in perfect balance and it survives just fine. Unless you're constantly spinning it over 6500 rpm, chances are a new balancer won't make a noticeable difference.

I have a balance sheet from one of the times I had my engine balanced. Using an internally balanced crank in an engine designed for external balance has it's own issues since it has an extra counterweight inside which made it hard for them to drill the crank to add heavier weight. In the end, they spun the crank 12 times to get the balance weight down to 0.0 grams.

I have to use an SFI neutrally balanced flexplate and it's date coded. Flexplate needs to be replaced every 3 years. I don't tear my engine down to get it rebalanced every 3 years. It's very unlikely my engine balance is still 0.0 grams but it's better than a randomly assembled engine being a few hundred grams out of balance.

Even simple things like wrist pins are not the same. I needed a replacement once and needed to know the weight of one of the others so the new wrist pin would match the rest for weight. It's hard to change the weight of tool steel wrist pins.