This is where we had been having all of our engines balanced for years and always had great results, but frankly, I had been concerned about the age of the machine. I was assured by older experienced colleagues in the business that I had nothing to worry about. A view of lots of equipment unveiled an older balancing machine made by Stewart Warner.
I questioned our host, technical director Dr. Andy Randolph, about the old machine and he informed me that the old machine is in great condition and has won a lot of races and championships. Randolph cleared up any concerns that I had about my own old machine. Advertisement Engine balancing principals have not changed for years but the balancing machines have.
Although they have not really gotten any more accurate the ease of completing a job has been made much easier. I will say, though, that if you elect to upgrade there are plenty of solutions on the market not only for an upgrade, but replacement as well.
I am happy with my old one. In our book, engine balancing has to be one of the top three upgrades that you need your customer to buy into when selling an engine or parts where the assembly needs to be balanced. Every aspect of what balancing accomplishes must be relayed to your customer for them to understand the value of the results.
This is where you can use your technical details that you have learned over the years to explain the benefits. Advertisement A balance job will typically come in one of two different ways; usually as some type of engine build or in pieces. If it comes in as an engine job you are less likely to have problems with the balance job.
If you are controlling the part purchases it makes it even easier. The goal is to not let the parts weight get too far away from what the present bob weight is so you can keep cost down. Sometimes you will have no choice if the customer is trying to lighten up pistons and rods, but at least you can keep it under control or advise him on increased balancing costs. Stop giving your time away on balance jobs!
Probably the most troublesome cases of engine balancing is when the customer has purchased his own parts and has brought them to you to balance. Ninety percent of the time the weight of the components are not matched close to what the crankshaft bob weight needs to be.
All this is fine and dandy and can be dealt with of course, but you need to advise your customer upfront that the balance cost will be more due to the increased work. We have all been trapped by this one time or another and need to leave an opening for additional cost.
You look at the parts and you can see that the crank is heavy and may even say that the bob weight required is 1, grams, but you can also see that the rods and pistons appear very light. In another case, the customer brings in a replacement lightweight crank with a required 1, grams of bob weight, but his used pistons and rods weigh much more than that. Advertisement In either case this job is going to be hours more than they ever expected, especially if the crankshaft is material plus the cost of heavy metal when on the light side.
What do you do? We need to educate customers on rotating assemblies so we can help them manage bob weight issues. Adjustments are usually necessary and the cost of the first balance job almost becomes wasted.
So, we are at the middle of the balance job. Be sure to have grams of oil on your balance data sheet calculation as well. Advertisement Normal caution for material removal on pistons and rods should be exercised. Quality pistons and rods very rarely need to have material removed to match balance. Case in point, pistons or connecting rods that have varying weights across the cylinders produce vertical forces as a result of the reciprocating motion.
Likewise, an imbalance will result from the rotation of the crankshaft or flywheel if the web weight of the crankshaft and weight distribution flywheel are uneven. At low speeds, the vibrations may not be noticeable but will be as you accelerate. Cylinder Layout. In some cases, even with a perfectly-balanced mass of components, imbalance may still occur as a result of cylinder layout.
When the forces from respective cylinders fail to cancel each other out, it can cause a resultant force or vibration. An inline-four engine, for instance, has intrinsic vertical vibrations which create an imbalance. This imbalance is unavoidable but manageable with the application of balancing shafts. Engine imbalance can be any of the following:. These imbalances can lead to reciprocating, rocking, and torsional vibrations. Engine balancing has the following benefits:.
Mechanics and automotive engineers try to achieve engine balancing. The fact, however, is that no engine can be perfectly balanced, due to various complex factors involved in the process.
Engine balancing involves the design, production, operation, and maintenance factors of the engine, amongst others, each benefiting from being balanced. Some of the factors to consider are:. Steps to Balancing an Engine. There are two steps involved in correcting an imbalance. Static Balancing. The first step aims to ensure that the piston and connecting rod weights are even.
Even loads result in equal inertia when these parts move. Crankshaft Balancing. This step involves spinning the crankshaft independently to ascertain if there is a rotational imbalance. In case there is a rotational imbalance, weight is added or removed until a smooth rotation is achieved. Smooth rotation eliminates the vibration caused by rotational imbalance. A balanced engine runs smoothly and can sustain higher engine speeds without getting damaged.
Advertisement The really tricky part is balancing the reciprocating forces inside a V6 or V8 engine. Unlike rotating forces that spin around an axis of rotation, reciprocating forces are moving back and forth. In a single-cylinder engine, there is nothing to counter these forces except the counterweight on the crankshaft.
If the mass of the counterweight equals the weight of the upper half of the rod, piston, wrist pin and rings, the forces will be balanced and the engine will run smoothly. Balance between the crankshaft and its related components is critical to providing a smooth, trouble-free powerplant. With a horizontally opposed four-cylinder engine, two pistons are always moving in when two pistons are moving out. Consequently, the forces, equal and opposite, are essentially balanced provided the weights of each piston and rod assembly is equal.
Balancing these types of engines is fairly simple because all you have to do is equalize the weights of the piston and rod assemblies. Advertisement With an inline four-cylinder engine, two pistons are moving up while two pistons are moving down. The motions of the pistons offset each other, but because they are not horizontally opposed the crankshaft needs counterweights to offset the reciprocating forces.
Things get much more complicated when we start talking about V6 and V8 engines, because one bank of pistons is moving at an angle to the other bank of pistons.
This creates force interactions that need to be offset by carefully positioned counterweights on the crankshaft. Advertisement A few extra grams also needs to be added to compensate for oil in the bearings and clinging to the parts. The total mass you end up with is what the counterweights have to equal to balance the engine.
For example, if each piston weighs grams, the wrist pins weigh grams, the ring set weighs 60 grams, and the small end of the rod weighs grams, the total reciprocating weight for each piston and upper rod assembly is grams. Take half of that amount grams , then multiply by two and we end up with grams of reciprocating weight that needs to be offset by counterweights on the crankshaft.
To that, we have to add the rotating weight of the big end of each connecting rod and bearing grams , also times two because there are two rods per journal. What we end up with is a combined weight of grams that the counterweights have to offset to balance the engine. The crank is then balanced to the bobweights, usually by drilling the counterweights to equalize the forces.
Counterweights can also be milled to remove weight for a cleaner, more aerodynamic result, but this requires removing the crank from the balancer and removing the bobweights so the crank can be milled, then carefully reinstalling the bobweights in the exact same position as before and respinning the crank to see if additional corrections are needed.
Advertisement With degree V6 engines, the angle between the pistons is less so a different value must be used when calculating the reciprocating mass for the bobweights. The value may also vary depending on whether or not the engine has balance shafts. The balance shafts have offset weights that help counter both engine dynamic vibrations and vibrations caused by uneven firing orders.
This can be done by drilling holes in the counterweights and installing heavy metal tungsten Mallory plugs. This is called externally balancing the engine. Advertisement Internal balance is always best because it keeps the offsetting weight closer to the reciprocating forces that need to be balanced.
Moving the weight out to either end of the crankshaft can sometimes create additional dynamic forces that cause vibrations of their own. Also, changing the index position of the flywheel or harmonic balancer on an externally balanced engine or replacing either component will upset the balance.
On most V8 cranks, there are only six counterweights to save cost and reduce weight. The counterweights are positioned in such a way that they offset not only the piston and rod assemblies on their own journals but also the adjacent journals. Some racing cranks are available with eight counterweights two for each pair of pistons , which often helps reduce high RPM vibrations even better, especially on long stroke cranks. Advertisement Crankshaft counterweights are typically made to a specific target bobweight.
In other words, the size, positioning and mass of the counterweights is designed to offset a specific piston and rod weight, plus or minus a couple percentage points. With stock cranks, the bobweight is more or less equal to the weight of the stock pistons and rods. If the rods and pistons are lighter than the crankshaft target bobweight, the counterweights will have to be drilled or milled to balance the engine. Advertisement This is important information to keep in mind if you are using parts from different suppliers, or are replacing one set of pistons or rods with a lighter set of pistons or rods.
You may end up with a mismatch that requires a lot of drilling or milling to achieve proper balance. Neutral balance works best in most applications because all the forces are offset and equal. But in some high-revving performance applications such as NASCAR where an engine may be running at 8, to 9, RPM or higher for most of a race, this may not be enough.
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