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I wanted to do some reverse engineering in an effort to determine what kind of balance factor was used by the Excelsior factory to balance the 61” Big X engines. For this test, I’m dealing with the 1916-1924 61” Excelsior twins which used common crank assembly parts for those years.
First a few observations and some details:
1. I have seen many X flywheels from these engines and none of them show any signs of having any balance work done on them. There are no drill or grind marks anywhere on these flywheels and no additional weight added anywhere. It appears that the X engineers did their balancing homework ahead of time, then simply cast the flywheels all the same, assuming that if all the components are made within some acceptable range of specification, that would be close enough.
2. Engine specifications: 61 cubic inches, Bore = 3.328” Stroke = 3.5”
3. I used all original X components. These are used parts, but all in very good condition. Since they are worn, my measurements are off some, but all in all should get close to determining the original balance numbers.
4. Cast iron pistons with 3 rings. Weight of the entire piston assembly with pin is 764 grams. Since I only have one good original complete piston assembly I assumed the same weight for both piston assemblies.
5. Cast iron spoked flywheels, diameter is 9 ¾”. Weight is approximately 12.5 lbs per wheel, not including the drive shafts.
6. Weight of crank pin assembly with bearings, cages, nuts and locks: 464.6 g
7. Rods, forged steel with non replaceable races, the big end is hardened and the rollers run directly on the rod. This was standard X practice through 1924. Length between hole centers is 8 3/8”. Total weight of each rod is within 2 grams of each other. Also interesting to note that the wrist pin end is actually heavier than the crank pin end by a ratio of about 55% to 45%, much different than Indian and Harley! The X rods were very spindly things indeed! The numbers are as follows:
• Front (forked) rod total weight: 468 g. Crank end = 222.6 g. Wrist pin end = 245.4g.
• Rear rod total weight: 466g. Crank end =209 g. Wrist pin end = 257g.
8. Weight of the entire crank assembly including rods, shafts, bearings and flywheels (no pistons) is approximately 29.6 lbs.
My first test was to use the common simple method of balancing as laid out in the Indian literature, early Harley literature and Uncle Franks musings as well as other early sources. . As mentioned in one book, “…….this is not necessarily an actual test of factory balance, however it is sufficiently close for all practical purposes.” And, “….you can obtain a very satisfactory balance by following this procedure for either Excelsior or Super X, Harley or Indian.”
This test requires assembling the entire crank with flywheels, shafts, bearings, cages, rods and one piston assembly with rings, pin and keepers attached to the male rod. This assembly is then laid on a set of parallels and should, in theory, be balanced, or at least close. I did this and used a passing wheel balance stand that I inherited a while back.
The results were not as expected! With one piston assembly attached, the piston instantly fell to the bottom, counter weight up. Not even close to being balanced! I removed the entire piston assembly and tried again. It was then very close to a perfect balance. I added small magnetic weights, 20 g. to the counter weight and 20 grams half way between the crank pin and counter weight on one side. This second weight makes sense as the spoked hole opposite this weight is a very rough casting and has additional material inside the hole. With these 2 small additional weights, and NO PISTON attached, I was able to obtain almost a perfect balance! So, according to the old method, this crank should be horribly out of balance! Keep in mind each cast iron piston assembly weighs764 g., so this means the counter weight is light by just about that amount! That’s a lot of weight!
Next, I disassembled the entire crank assembly and weighed each component. Then I balanced each flywheel separately by adding weight to the crank pin bob weight. The weights required to balance each flywheel individually were then added together. This represents the theoretical weight needed to balance the 2 flywheels when assembled. These numbers were entered into the standard S&S balancing work sheet. Once I did this, simply working from both ends of the work sheet, I was able to calculate the balance factor for this setup. I came up with a balance factor of 23.3% which is crazy! General consensus seems to be in the 50 to 60% range for most V twins but the exact number is an area of great debate. However, this 23.3% number does correlate with the general rule of removing more weight from the flywheel counter weight to achieve a lower balance factor.
Looking at things from a different angle, I entered all the weights into the S&S worksheet and, for the sake of comparison, used a 60% balance factor. Working through the math on the worksheet yields a bob weight of 1057.1g. per flywheel. Compare this number with the actual weight which I found will balance one flywheel as it is (averaged to 684.6) and there is a huge difference, of 372.6g.! This means in the original configuration, the counter weight of each flywheel is 372.6 g. too light to balance this crank assembly at 60%. If I do the math with say a 50% balance factor, the counter weight of each flywheel is 271.6 g. too light. If my numbers are correct, I understand this to mean that in order to balance this crank by today’s standards, I would need to either add considerable weight to the counter weight of each flywheel (271- 372 g. depending on balance factor used) or remove a comparable amount from the crank pin area of the flywheels. This seems outrageous and may not even be possible.
When it comes time to actually balance my ‘24 crank assembly, I will be using aluminum pistons. The difference in weight should be significant and will reduce those crazy bob weight imbalance numbers quite a bit, but still will be way off.
So, I see a few possible answers to the glaring imbalance (pun intended) of the numbers:
1. My math is all wrong! I’ve double, even triple checked the numbers, but I’ve been consistently wrong before!
2. Excelsior engines were horribly out of balance!
3. The “arbitrary” balance factors of 50-60% are not that important.
Now, I will admit, because I’m using worn components which came from different engines, this is not anywhere near a perfect test. However, I’ve cleaned and fitted these parts carefully and am quite sure this is a correct assembly of parts for the application. So, I should at least be close to some commonly accepted balance factor or standard but the results show otherwise.
I’m anxious to hear input from others that understand balancing better than I do and especially anyone who has balanced Excelsior engines in the past and then ridden them to see how they actually perform.
I remember Brad Wilmarth telling me that the early X flywheels do not have enough counter weight in them so either add counter weight or remove weight from the crank pin side of the flywheels. Steve Huntzinger confirms this and swears by the early method of balancing for the older machines.
Gene Harper
12/31/2015
IMG_0380.jpgIMG_0387.jpgIMG_0386.jpg
First a few observations and some details:
1. I have seen many X flywheels from these engines and none of them show any signs of having any balance work done on them. There are no drill or grind marks anywhere on these flywheels and no additional weight added anywhere. It appears that the X engineers did their balancing homework ahead of time, then simply cast the flywheels all the same, assuming that if all the components are made within some acceptable range of specification, that would be close enough.
2. Engine specifications: 61 cubic inches, Bore = 3.328” Stroke = 3.5”
3. I used all original X components. These are used parts, but all in very good condition. Since they are worn, my measurements are off some, but all in all should get close to determining the original balance numbers.
4. Cast iron pistons with 3 rings. Weight of the entire piston assembly with pin is 764 grams. Since I only have one good original complete piston assembly I assumed the same weight for both piston assemblies.
5. Cast iron spoked flywheels, diameter is 9 ¾”. Weight is approximately 12.5 lbs per wheel, not including the drive shafts.
6. Weight of crank pin assembly with bearings, cages, nuts and locks: 464.6 g
7. Rods, forged steel with non replaceable races, the big end is hardened and the rollers run directly on the rod. This was standard X practice through 1924. Length between hole centers is 8 3/8”. Total weight of each rod is within 2 grams of each other. Also interesting to note that the wrist pin end is actually heavier than the crank pin end by a ratio of about 55% to 45%, much different than Indian and Harley! The X rods were very spindly things indeed! The numbers are as follows:
• Front (forked) rod total weight: 468 g. Crank end = 222.6 g. Wrist pin end = 245.4g.
• Rear rod total weight: 466g. Crank end =209 g. Wrist pin end = 257g.
8. Weight of the entire crank assembly including rods, shafts, bearings and flywheels (no pistons) is approximately 29.6 lbs.
My first test was to use the common simple method of balancing as laid out in the Indian literature, early Harley literature and Uncle Franks musings as well as other early sources. . As mentioned in one book, “…….this is not necessarily an actual test of factory balance, however it is sufficiently close for all practical purposes.” And, “….you can obtain a very satisfactory balance by following this procedure for either Excelsior or Super X, Harley or Indian.”
This test requires assembling the entire crank with flywheels, shafts, bearings, cages, rods and one piston assembly with rings, pin and keepers attached to the male rod. This assembly is then laid on a set of parallels and should, in theory, be balanced, or at least close. I did this and used a passing wheel balance stand that I inherited a while back.
The results were not as expected! With one piston assembly attached, the piston instantly fell to the bottom, counter weight up. Not even close to being balanced! I removed the entire piston assembly and tried again. It was then very close to a perfect balance. I added small magnetic weights, 20 g. to the counter weight and 20 grams half way between the crank pin and counter weight on one side. This second weight makes sense as the spoked hole opposite this weight is a very rough casting and has additional material inside the hole. With these 2 small additional weights, and NO PISTON attached, I was able to obtain almost a perfect balance! So, according to the old method, this crank should be horribly out of balance! Keep in mind each cast iron piston assembly weighs764 g., so this means the counter weight is light by just about that amount! That’s a lot of weight!
Next, I disassembled the entire crank assembly and weighed each component. Then I balanced each flywheel separately by adding weight to the crank pin bob weight. The weights required to balance each flywheel individually were then added together. This represents the theoretical weight needed to balance the 2 flywheels when assembled. These numbers were entered into the standard S&S balancing work sheet. Once I did this, simply working from both ends of the work sheet, I was able to calculate the balance factor for this setup. I came up with a balance factor of 23.3% which is crazy! General consensus seems to be in the 50 to 60% range for most V twins but the exact number is an area of great debate. However, this 23.3% number does correlate with the general rule of removing more weight from the flywheel counter weight to achieve a lower balance factor.
Looking at things from a different angle, I entered all the weights into the S&S worksheet and, for the sake of comparison, used a 60% balance factor. Working through the math on the worksheet yields a bob weight of 1057.1g. per flywheel. Compare this number with the actual weight which I found will balance one flywheel as it is (averaged to 684.6) and there is a huge difference, of 372.6g.! This means in the original configuration, the counter weight of each flywheel is 372.6 g. too light to balance this crank assembly at 60%. If I do the math with say a 50% balance factor, the counter weight of each flywheel is 271.6 g. too light. If my numbers are correct, I understand this to mean that in order to balance this crank by today’s standards, I would need to either add considerable weight to the counter weight of each flywheel (271- 372 g. depending on balance factor used) or remove a comparable amount from the crank pin area of the flywheels. This seems outrageous and may not even be possible.
When it comes time to actually balance my ‘24 crank assembly, I will be using aluminum pistons. The difference in weight should be significant and will reduce those crazy bob weight imbalance numbers quite a bit, but still will be way off.
So, I see a few possible answers to the glaring imbalance (pun intended) of the numbers:
1. My math is all wrong! I’ve double, even triple checked the numbers, but I’ve been consistently wrong before!
2. Excelsior engines were horribly out of balance!
3. The “arbitrary” balance factors of 50-60% are not that important.
Now, I will admit, because I’m using worn components which came from different engines, this is not anywhere near a perfect test. However, I’ve cleaned and fitted these parts carefully and am quite sure this is a correct assembly of parts for the application. So, I should at least be close to some commonly accepted balance factor or standard but the results show otherwise.
I’m anxious to hear input from others that understand balancing better than I do and especially anyone who has balanced Excelsior engines in the past and then ridden them to see how they actually perform.
I remember Brad Wilmarth telling me that the early X flywheels do not have enough counter weight in them so either add counter weight or remove weight from the crank pin side of the flywheels. Steve Huntzinger confirms this and swears by the early method of balancing for the older machines.
Gene Harper
12/31/2015
IMG_0380.jpgIMG_0387.jpgIMG_0386.jpg
On my '16J, I'm using H-D cast iron pistons, and original internals so I expect to have what Harley-Davidson deemed acceptable in 1916. Knowing your expectations, and probable road run use for the Excelsior, Gene, I would balance to improve a short-coming in that motor that you find irritating. I'm sure I'm not telling you anything profound, but in my experience, it is vibration at higher speeds that I find the most aggravating. I'm a total neophyte about balancing, but can dynamic balancing more accurately map where the sweet spot will be in RPM?
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