Balance a Burtz

I had actually been thinking about this a bit myself as I'm inching slowly towards building up my Burtz engine. The Burtz crankshaft is "balanced" and the connecting rods matched, but since the Burtz package does not include pistons, rings, pins, etc. then a reciprocating weight (pistons, etc.) would have to be assumed for that crank balance. And a flywheel weight would have to be assumed.

I separately emailed John Lampl asking this question.

FWIW, a number of folks in my club have built and installed Burtz engines and I've not heard of anyone who has done additional balancing. Lacking other information, I would assume that at typical touring rpms there would not need to be anything more, and I'm not planning to balance with my pistons.
 
I believe the crank and rods are already balanced, Pistons are normally factory balanced too. It's not a bad idea to have them all checked anyway.
 
I just got this reply back from John Lampl:


Hi John,

The Burtz Block comes with a balanced crankshaft and connecting rods. The rods are all balanced to within 3 grams of each other and are manufactured to industry standard; the ends (large and small) are not necessarily balanced with each other. This is a performance standard and can be achieved by removing material from rods to achieve similarity on big and small ends. This is not a requirement for a standard build.

The flywheel is a separate item, and it is also balanced independently.

The crankshaft is balanced independently of any reciprocating weight/parts.

I hope this helps.

Thanks,
John

​
So yes, the parts are independently balanced, but not as an assembled unit. If you are going to build a high rpm hill climber then you might want to do some additional work, but for normal operation I'm not planning to do more. Already that's an improvement over the standard A engine.

And that, my friends, is about the limit of my knowledge on the subject! Any more - consult your friendly local Banger speed shop or engine builder.
 
I'm going to send my Burtz engine parts to the balancer. Going to start my build first of the year. I'll report the results.
 
BrianH said:
I'm going to send my Burtz engine parts to the balancer. Going to start my build first of the year. I'll report the results.
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Brian - I'll be very interested in hearing how much your balancer needs to adjust. What pistons are you using?
 
I had my Burtz flywheel and pressure plate balanced by Tom at Auto
Dynamic Balancing.


[FONT=&quot]AUTO DYNAMIC BALANCING[/FONT]
[FONT=&quot]5136 Heintz St[/FONT]
[FONT=&quot]Baldwin Park, CA 91706[/FONT]
[FONT=&quot](626) 962-9135[/FONT]
 
Dynamic balancing of a crankshaft requires collars to be machined that weigh the same as the weight of the con rod at the big end and a portion of the the weight of all the components at the small end of the con rod. That would include the piston, pin, and rings. The proportion is usually between 65% and 70%. The collars go onto the rod journals of the crankshaft when it is dynamically balanced.

100% of the weight at the small end is not used because this weight only effects the balance of the crankshaft when the pistons are changing direction at the top and bottom of the stroke. The weight at the small end of the rods does not pull on the crankshaft when the pistons are at about mid stroke. The dynamic balancing is a compromise because an inline engine like the Model A can never be 100% balanced. A different counter balance weight is needed when the pistons are at the top and bottom of the stroke than when the pistons are mid stroke.

Years ago I invented a method to 100% balance a reciprocating engine but it is not a practical solution.
 
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Having built 18 Burtz engines so far, I have found in most cases, the "factory" balance is satisfactory. Most of the engines were good but some were a little better and some were not quite as smooth as others. On all of them, I did have the clutch balanced to the flywheel. In the process of balancing the clutch, the flywheel balance was checked and corrected as necessary by itself. When I finished engine #14, I found I had a problem. It was definitely not as smooth as the others and the customer was not at all satisfied, which I did not blame him. This engine will have to come apart and corrected. John Lampl has been very supportive and will do what is right to take care of the problem.

To keep from having this problem again, I am checking the balance of the components for the rest of the engines before assembly.

My experience,

Chris W.
 
nkaminar said:
Dynamic balancing of a crankshaft requires collars to be machined that weigh the same as the weight of the con rod at the big end and a portion of the the weight of all the components at the small end of the con rod. That would include the piston, pin, and rings. The proportion is usually between 65% and 70%. The collars go onto the rod journals of the crankshaft when it is dynamically balanced.

100% of the weight at the small end is not used because this weight only effects the balance of the crankshaft when the pistons are changing direction at the top and bottom of the stroke. The weight at the small end of the rods does not pull on the crankshaft when the pistons are at about mid stroke. The dynamic balancing is a compromise because an inline engine like the Model A can never be 100% balanced. A different counter balance weight is needed when the pistons are at the top and bottom of the stroke than when the pistons are mid stroke.

Years ago I invented a method to 100% balance a reciprocating engine but it is not a practical solution.
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The above is true on other than 4 cylinders, they only need balancing of individual parts, so independently is the way they are done.
 
nkaminar said:
Dynamic balancing of a crankshaft requires collars to be machined t
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Any balancing shop will have a universal set of adjustable bobweights,


How do you calculate Bobweight?




An 1,800-gram bob weight is basically the amount of weight in each of the counterweights. However, you don't just add all the values up to determine bob weight. The formula is 100 percent of the rotating weight plus 50 percent of the reciprocating weight.
 

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Guys- inline four cylinder engines do not require the use of bob weights to balance the crankshaft. Regarding the connecting rods, a through balance job will require rebalancing the connecting rods using the big end and total weights. The Burtz rods, as far as I know, are balanced for total weight only. This might be 'good enough" for some folks but on a multi thousand $$ motor, why take a chance?? Just my opinion.
 
nkaminar said:
Dynamic balancing of a crankshaft requires collars to be machined that weigh the same as the weight of the con rod at the big end and a portion of the the weight of all the components at the small end of the con rod. That would include the piston, pin, and rings. The proportion is usually between 65% and 70%. The collars go onto the rod journals of the crankshaft when it is dynamically balanced.
Click to expand...

Some clarity of terms might be useful here.

1 - The "collars" are called "bob weights".
2 - Dynamic balancing is balancing over the whole length of the assembly.
3 - Static balancing is balancing in a single plane.
4 - When balancing the crank either with or without bob weights, it is
static balanced first and then dynamic balanced.
5 - Normally, single plane crank assemblies such as the model A/B are only
balanced with bob weights when the engine is used for racing. The
percentage of balance will determine the smoothest operating range which
for 70% is in the 6500 to 7500 area. The operating range can be adjusted
up or down by the percentage.
 
Here is a video of a crankshaft being dynamically balanced. You can turn the sound off as it is just some obnoxious "music." https://www.youtube.com/watch?v=jVF7xezos78

My first job out of college was fixing a balancing problem on a gas turbine engine. It turns out the operator of the balancing machine did not know what they were doing. I had to educate myself and then find an employee who was capable to understanding instructions. That was 60 years ago so I am sure the technology has improved, but the principles are the same. When building racing motor cycle engines I had to machine my own collars to use as bob weights.
 
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