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Engine Rebuilding - Flywheel Balancing , Fitting Pistons, Torque ( Excelsior 17/18)

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  • #16
    Bosch ZEV and others,

    Below is a copy of a write up I did few years ago regarding the Excelsior balance question. I still haven't decided exactly what I'm going to do, but I'm leaning toward the old method of balancing the entire crank assembly with one piston on a passing wheel balance stand. I'm sure this will open up lots more ,,,,, well, discussion!


    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_0383.jpgIMG_0380.jpg

    Comment


    • #17
      Good grief, Gene.

      You've made this much more complicated than it is.

      If you 'hang' the assembled crank with rods (as shown in your pic), you don't need the rotating weights (or make any "bob weights");
      Just add mass on the wristpin ends until it comes to balance. Weigh that, add the 'wrist pin ends', and divide that total by the real total reciprocating weight.

      That gives you the real, existing factor. Then you can change it as you please.

      ....Cotten
      PS: Please note, Folks,..
      S&S either presumed dynamic balancing where rods cannot be installed, or their compact knife-edge product that also prohibits the rods, both requiring faking with bob weights, twice the truing procedure, introducing three times the 'error', and takes ten times the patience.
      Last edited by T. Cotten; 04-30-2020, 10:57 AM.
      AMCA #776
      Dumpster Diver's Motto: Seek,... and Ye Shall Find!

      Comment


      • #18
        Cotten,

        OK, that was my first dip in the balancing pool. I have the equipment to balance using the S&S method, or the assembled crank method. Note that the crank was very close to being balanced when assembled, with NO PISTON installed on either rod! If I installed one piston assembly on a rod, as is customary, I would then need to add virtually that same amount of weight to the counterbalance end to get it to balance again, or remove that much weight from the crankpin area. That's nuts! This tells me X was doing something quite different from everybody else but I'm not sure what, or why.

        Regarding the theory that the motor needs to be balanced a certain way based on the type of frame, well somebody please explain that to me, and more importantly, how to balance it so it works in a spindly, wiggly keystone frame of 1915 design!

        Now that I'm getting closer to actually balancing the real setup, things will change a fair amount, as I'll be using aluminum pistons, so I'll start there and see where to go. I think I'll not use the S&S Method, yes it is cumbersome and lots of room for error!

        Comment


        • #19
          I know nothing of your frame, Gene,..

          But my previous link gives some clues: http://virtualindian.org/Flywheeltheory3.htm.
          How is the motor secured?

          Back to the flywheels, your pic seems to show some very unique 'windows' in them.
          Is there a symmetrical round window behind your balancer?
          Thanks!

          ....Cotten
          Last edited by T. Cotten; 05-01-2020, 10:57 AM.
          AMCA #776
          Dumpster Diver's Motto: Seek,... and Ye Shall Find!

          Comment


          • #20
            Cotten,

            Yes, the flywheels have symmetrical holes. Frame is a keystone frame. The engine and transmission are held in place by 1/4" steel plates and 7/16" studs. Sounds robust but it's quite flexible! Top motor mounts attach to the lower tank tube, but again, quite a flimsy set up.

            Gene

            IMG_0386.jpg1924 X pg 8.jpg

            Comment


            • #21
              I wouldn't know a Keystone if it bit me, Gene!

              It would appear the motor receives nearly all of its support at the plates, as the removeable top mount is scary.

              Attempting to understand Mat Elvenkemper's explanation at http://virtualindian.org/Flywheeltheory.htm, it would seem we would want a very high factor.

              The countermass of your wheels is so dramatically small, and so close to the mains, it would seem to suggest that's impossible.

              ....Cotten
              PS: Damn those are long rods....
              Its pretty *unusual* for the wristpin ends to be heavier than the other!

              And I gotta ask: Isn't one rod 'forked', and the other a 'blade'? Yet the rods only differ by two grams?

              Wow. Must have something to do with that 'heel' sticking out the bottom of the 'front' rod.
              Last edited by T. Cotten; 05-02-2020, 02:05 PM.
              AMCA #776
              Dumpster Diver's Motto: Seek,... and Ye Shall Find!

              Comment


              • #22
                Is there NO top motormount, Gene?

                *gasp*

                ....Cotten
                AMCA #776
                Dumpster Diver's Motto: Seek,... and Ye Shall Find!

                Comment


                • #23
                  Yes there is, of sorts..... a 1/4" steel angle attached to a 3/8" stud on the top of the cylinder. This attaches to the removable lower tank tube with a 5/16" bolt. To make matters worse, the tank tube is relatively thin walled tubing and even the 5/16" bolt will smash the tubing. So yes, but not very solid, just like the rest of the chassis!

                  I'm making a few changes to stiffen mine up....

                  Gene

                  Comment


                  • #24
                    The photographed ad correctly refers to the upper horizontal bar as "in compression". This is true both of the chassis weight and torque reaction.
                    If it can be done without mods to the tank etc. this should really be the largest diameter tube you can fit, regardless of the size of the attachment bolts. If invisible, a tall rectangle may be better than a round tube.
                    The Linkert Book

                    Comment


                    • #25
                      If the frame is 'stiffened', Folks,..

                      Then the original factor becomes meaningless.

                      Have you tried to determine it yet, Gene?

                      (History says it worked well.)

                      ....Cotten
                      PS: Finally found this '42 Quartermaster pic; The pinion shaft is similar to Indians, and note the balancing holes are by the crankpin!
                      Attached Files
                      Last edited by T. Cotten; 05-06-2020, 11:54 AM.
                      AMCA #776
                      Dumpster Diver's Motto: Seek,... and Ye Shall Find!

                      Comment


                      • #26
                        Cotten,

                        As mentioned in my initial diatribe, I came up with a balance factor of about 23%, which is nuts! Confirming this somewhat is the fact that on parallels, the crank assembly is almost perfectly balanced with NO piston attached. Attaching the piston makes it drop like a rock to the bottom of a pool!

                        Kitabel, I have replaced the lower tank tube with one of the same diameter (1 1/8") but this tube has 1/4" wall thickness, compared to the .060" original. This should help considerably. There is no room for a larger OD tube and square or larger would not look correct anyway. Yes, it is under tension, sort of.......

                        Gene

                        Comment


                        • #27
                          That would seem pretty improbable, wouldn't it, Gene?

                          The pistons would throw themselves right through the removable member!

                          It still bugs me that the tops of your rods are so much heavier than the bottoms.

                          I mean,... just look at them. Do they look that way to you?

                          ....Cotten
                          PS: At least maybe if the rod tops are really that massive, you could carve on them to raise your factor!

                          PPS: Attached is a pic of my adjustable lubed ball-chain hanging apparatus for weighing rods, which proved far more reproduceable than other approaches.
                          And I made a level with adjustable pucks to fit the rods for certainty when setting it up.

                          Never did I encounter a rod where the top was even close to the bottom.
                          Attached Files
                          Last edited by T. Cotten; 05-07-2020, 12:55 PM.
                          AMCA #776
                          Dumpster Diver's Motto: Seek,... and Ye Shall Find!

                          Comment


                          • #28
                            Tension - compression = opposites.
                            The wall thickness change is about 150% more stiffness (2-1/2 X the original).
                            The Linkert Book

                            Comment


                            • #29
                              Cotten,

                              Yes, the X rods are different than most. The big end is super thin and spindly, the tops are heavy. To make matters worse, the big end does not have a replaceable race, nor is there room to fit one in. The race is case hardened and the rollers run directly on the rod! X did this from day 1 through 1924. Super X came out in '25 and they finally went to a replaceable race and much heavier big end.

                              Back to the balance issue: Yes, my balance factor calculation of 23% is insane! Again, it is generally confirmed by the fact the crank assembly essentially balances with no piston attached. Sounds NUTS! But, they did that for 15 years or so and remained a force to be reckoned with!

                              I'll start from scratch and balance the assembly on my passing wheel stand.

                              Kitabel, thanks for the data. That may be the strongest piece on the entire motorcycle!

                              Comment


                              • #30
                                Its certainly a mind-boggle, Gene!

                                The rod tops alone are a quarter of the reciprocating weight, and even heavier than the rod bottoms, pin, and hardware.

                                But the rod assembly is about half and half to itself, if that's a clue.

                                They must have expected the flymass to dampen the forces, along with combustion? We have to be missing something...!

                                ...Cotten
                                PS: What was the angle of the cylinders?
                                Last edited by T. Cotten; 05-10-2020, 11:09 AM.
                                AMCA #776
                                Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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