Over the years I’ve seen many articles on engine balancing and it seems that most of them get pretty technical and complicated. It is always nice to understand the depth of what you are trying to accomplish, but we cannot lose focus of the ultimate goal – which is to give the customer the best-balanced engine that we possibly can.
We are not going to get too technical in this article but just relay some information that might assist you in a sale or a thought that might help you in your balancing process. Our goal is to give you the engine balancing routine that we use at our shop along with a few technical thoughts, insights and a few real world stories.
We all know the routine on how to set up for balancing. Making sure either you or the customer has selected all the correct parts, weighing and adjusting the pistons and rods to match each other, setting up the bob weights and of course making a balance data sheet that your customer can have. Let’s face it, we can talk technical all day long about balancing but we need to remember that the balancing machine does most of the work for us.
And many of those machines have been doing a great job for a long time. In 2009, we bought out a small balancing business that had been around for many years and came with an older Stewart Warner machine with analog display. 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.
I remember a trip back in 2012, when I had the opportunity to view the engine build operation at the Earnhardt Childress Racing Engines (ECR) facility in Welcome, NC. 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. Dr. Randolph cleared up any concerns that I had about my own old machine.
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. So my point is, as long as your machine is calibrated and in proper working order, I don’t think the age of the equipment will matter. 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.
There are many older folks out there who don’t believe in the benefit of balancing, because they know in the past that they could get away without it. But as we all get better at engine builds using today’s aftermarket components and machining precision we have got to get through to this older generation that proper balancing is critical to the life expectancy of the engine. It’s a fact; engine balancing adds life to any engine. This is where you can use your technical details that you have learned over the years to explain the benefits.
In reality, most of the time if you explain the type of imbalance that occurs when just 5 grams is out of place and 3˝ or more off the center line of the crankshaft, they usually buy in with no problem. Coupled with what they might have read on engine balancing and their buddies’ advice after having an engine balanced, the sell becomes a bit easier.
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.
And it’s critical that we talk about cost. 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. As an example, our hourly shop rate is $92/hour, and a typical cast iron crank and assembly usually takes us about two hours of time for an approximate total of $180 for a V8 balance job. But you’ve probably seen this example: a rotating assembly comes in and the customer brags about how much money he saved by buying parts separately. You look at the parts and you can see that the crank is heavy and may even say that the bob weight required is 1,850 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 1,610 grams of bob weight, but his used pistons and rods weigh much more than that.
In either case this job is going to be 1-3 hours more than they ever expected, especially if the crankshaft is 4340 material plus the cost of heavy metal when on the light side. What do you do? If you’re like many of us, you feel sorry for the customer’s problem and never charge enough for your time.
Yes, it is a difficult lesson for the customer to learn but it’s an opportunity for you to let them know they should have purchased the parts from you instead of elsewhere so the weight could be managed. Now the savings on the parts they bought has to go to the balance job that went from $180 to $272-$365 plus heavy metal at $35 a piece. We need to educate customers on rotating assemblies so we can help them manage bob weight issues.
One other issue that crops up is a customer who has bought a rotating assembly that has already been balanced, but not with the harmonic balancer and flex plate/flywheel (the ends) in place. I’ve seen many of these assemblies go wildly out of specification when the ends are added on. 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. We’ve got all the reciprocating parts in, weighed all the parts and filled out a balance data sheet. If you don’t have a database that automatically gives the values after the weighted values are enter, I recommend getting one so errors can be minimized – it is the quality thing to do and can be built off of Microsoft database program very easily. Be sure to have 2-4 grams of oil on your balance data sheet calculation as well.
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. Be consistent on all the weight measurements when adjustments are necessary. The more detail in this area goes a long way down the road on quality results. Building the bob weights is very straightforward and again, making them accurate to the balancing data sheet calculation is critical. You should have half-gram weights available for maximum adjustment.
To further avoid any balancing issues we prefer to spin our assemblies all at once. An added effort to balance the harmonic balance/flex plate/flywheel/pressure plate (the ends) to zero initially will pay off handsomely. Be sure to index the pressure plate to the flywheel, this will assure a quality job. There will be some questions on how adjustments need to be made. With a complete assembly, efforts must be made to make all weight adjustments on the crankshaft. This is not always possible but, all efforts must be exhausted before making attempts to the ends. Externally balanced engines are a bit different and again should have minimal adjustments made on the ends with the majority on the crankshaft.
Making weight adjustments to the crankshaft or the ends can be complicated at times, which is why bob weight management is so important at the earlier stages. If properly managed it is ideal to have the bob weight slightly less than the crankshaft so minor drill hole adjustments can be made. Where it gets complicated is large 1˝ holes that may need to be drilled and is magnified by 5 when steel 4340 crankshafts are used. For drilling holes we typically pilot a hole before moving to the 1˝ drill. A slow consistent rotation will keep you in control of material removal and hopefully keep you from damaging tools.
As always, remove a little less than what is calculated because you can always take more out, but cannot put it back very easily. There are a couple of ways to add material. I have added a lot of heavy metal in my time and the most solid way to properly install, is to mount crossway in each end of the counter weights. We use an industry standard drill and reamer that will interfere fit the heavy metal by .002˝.
On the other side is adding heavy metal to the crankshaft. Unfortunately you need to have the drills and reamers for each size of the heavy metal that is available. We typically install the heavy metal out as far as we dare, but usually .075˝ from the end with a 4340 crank and .100˝ with cast. Each weight addition is different, but I can tell you that over the years we have successfully welded up existing holes to add the necessary weight and have never seen any repercussion from that effort so, I would advise that as a simpler or cost effective solution. Be sure to protect the journals at all times. After balancing, a final polish job and rinse on the crankshaft will show your customer a sign of quality.
The Next Opportunity
In conclusion, I hope this article was enough to give you another perspective on what others might be doing. I’m sure you have somewhat of the same theories and processes. The biggest encouragement that I can give you is that engine balancing can be very complicated with heavy decisions and some risk at times. Also, the closer that you make each of your weight adjustment the better you will be than the next guy. Don’t cut yourself short on your expertise and charge the full amount of time that you spent. You can do a less-than-average job and maybe get away with it, but the feeling when your customer returns saying, “It really runs smooth,” will be worth all your effort and is the best advertisement! ν