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Thread: Engine Balancing

  1. #1
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    Engine Balancing

    Any knowledge out there on balancing the Animal and World Formula. Looking for info on balancing engines running in the 7500 to 9500 RPM ranges. Is there any power or reliability to be gained? Is the engine really out of balance or is it just torque spikes from a single cylinder engine we feel?

    Thanks
    Steve

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    I don't have much knowledge to share Steve, I mainly wanted to post on the topic as it could become a good read to flag as others add their thoughts to it.
    The big torque spike during one of the four strokes has to be pretty hard to balance out at any rpm.

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    Thanks Freeze, we shall see what is posted. I think the knowledge is very limited as balancing these small engines is not very common at all. I did have a good talk with Steve Vermeer today and he educated me with his knowledge. Its a very interesting topic for sure.

    Steve

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    my limited knowledge is 20yrs old and applies to engines in general, but what i knew then was cutting edge and still i'm just seeing it addressed or 'seeping" out... and it is much more about harmonics than "static or rotating balance" we spent more than anyone at the time on high speed image capturing... stuff you could do now for a couple thousand dollars we spent millions on, had to go to sound to get the real picture, some stuff we believed to be true then went very much against conventional wisdom and I'm just now hearing that it is making it into competition situations, which means if i'm hearing about it as "new" it's been in use for a few years or more. but it is all RPM specific down to a single number... can you or can you not change/control the "balance/harmonics" on an engine while it is in operation

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    The best discussions I have seen on balancing single cylinder engines were in books published some years ago on building all types of racing motorcycle engines. That's the good news. The bad news is that somewhere along the line the book with the best description I remember disappeared due to a move or being loaned out and never returned. I remember pictures of the wristpin end of the rod resting on a precision scale and the paragraph that went with the picture stating that balancing of a one lunger consisted of applying some percentage of that weight (maybe also including the piston/wristpin and wristpin retainers?) against some other weight (the crankshaft counterweights?). Afraid I'm not much of a help, but this may give you a place to start looking.

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    I believe the word "balancing" when used in reference to a single cylinder engine is a misnomer. Not really sure what you actually "balance". Equalizing may be a better term but that would only refer to the components. Adding torque to the situation is well beyond my pay grade!

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    We should refer to it as vibration from this point on. What factors are causing vibration and what technical modifications can be done to reduce vibration. Also how can the vibration be shifted to different rpm ranges in order to reduce vibration in the primary rpm range you are racing in.
    Vibration is a form of energy loss that transfers this energy into power loss and vibration damage to surrounding components.

    Steve

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    Quote Originally Posted by Outrider View Post
    The best discussions I have seen on balancing single cylinder engines were in books published some years ago on building all types of racing motorcycle engines. That's the good news. The bad news is that somewhere along the line the book with the best description I remember disappeared due to a move or being loaned out and never returned. I remember pictures of the wristpin end of the rod resting on a precision scale and the paragraph that went with the picture stating that balancing of a one lunger consisted of applying some percentage of that weight (maybe also including the piston/wristpin and wristpin retainers?) against some other weight (the crankshaft counterweights?). Afraid I'm not much of a help, but this may give you a place to start looking.
    I'm sure this is one of the stupidest moves I have made recently, but, I will share the formula with you (I WILL NOT DEBATE IT).

    First, lets establish that there are two different kinds of weight moving around in the engine. Reciprocating (up and down of the rod and piston) and Rotating (spinning of the flywheel and crank). The single cylinder engine, with the Reciprocating motion going in only one direction, can not technically be balanced. However, you can move the vibrations to an RPM that is not used a lot, like very low RPM's. Now, to all the 'Nay-Sayers', if that isn't a form of balancing, I don't know what the heck is? This formula has been used by nearly all the Motorcycle racing departments back in the 20th century.

    Formula:

    A - Rotating Weight. (using Grams seems the most accurate)
    1. Suspend the rod by holding it by the wristpin and weight the large end keeping it parallel.
    2. Weight the crank pin or calculate the weight by using size and metal weight.
    3. Weight the associated bearings and thrust washers.
    4. Total all the Rotating Weights


    B - Reciprocating Weight:
    1. Suspend the rod by holding it by the large end and weight the wrist pin end keeping it parallel.
    2. Weight the Piston, Rings, Wrist pin and Clips.
    3. Total the Reciprocating Weight.

    C - Multiply (B) times the Balance Factor (Usually between 48%-65%. Anything above or below is hard to see any change. 64% was the factor we always used. It put the vibrations around 1-1.2K RPM).

    D - Balance Weight:
    Add the Rotating weight (A) to the Balance weight (C) and this is the amount of weight that has to be added to the flywheel assembly.

    Now find a set of 'knife edge' parallels and start adding your tungsten weights. Tungsten carbide is what you want to use as you add the weight to the assembly because it is the most dense metal that is not affected by heat or corrosion. It is also very expensive, so.... find a metal machine shop in your area and ask them if they have any old burnt up carbide mill bits and just cut off the solid end with a cut off wheel. I promise you that it will save you a bunch of money.

    Hope this helps.........

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    4 Cycle Advanced User Jimbo's Avatar
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    A while ago i had the best automotive machine shop in my area check the balance of a stock Animal crank with stock components (rod, piston, rings, wrist pin, clips)
    It was determined to just leave things as they were. They did not add or subtract any weight.

    The balance was not checked with the flywheel
    It also did not include the clutch. I see the clutch as somewhat of a problem since it doesn't always lock up in the same place and there is wear involved with the drum and shoes etc.

    We have automotive engines that are balanced internally and also externally via weights welded to the flex plate. I can tell you from experience that you don't want to use the wrong flex plate and ring gear assembly on one of these vehicles. The extreme vibration will make it will be un-drive-able. My experience was that it shook so bad i thought the dash ans steering column was going to come

    I wonder how effective it would be to re-balance a single cylinder engine via the flywheel. Will it accomplish what we want?

    I agree with your statement "Vibration is a form of energy loss that transfers this energy into power loss and vibration damage to surrounding components"
    It amazes / amuses me when i see karts with wheels way out of balance or body work that is bouncing around. I never remember seeing the people up front with these issue.

    Here's a very precise balancer that came out of the local Tecumseh plant when they closed.
    The bearings on the wheels are so free that if you blow on one of the wheels it will rotate.

    Click image for larger version. 

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    I believe in science.

  10. #10
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    I believe that in the MX motors having a full circle crank helps...
    Comparing a MX 125cc 2 stroke and a 250f four stroke... both rev to 14,000 rpm...
    Both do not vibrate much if at all...
    I do know that the 250f four stroke has a balancer...

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    Techbigdog, that is a perfect example of what I remember in the discussions of reducing/moving vibration in single cylinder engines in the lost book; thanks for the refresher. I also seem to remember the lost book mentioning 60-65% as a good starting point to keep vibrations in the low rpm range. Thanks again; it was a good trip down engineering memory lane.

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    Quote Originally Posted by Outrider View Post
    Techbigdog, that is a perfect example of what I remember in the discussions of reducing/moving vibration in single cylinder engines in the lost book; thanks for the refresher. I also seem to remember the lost book mentioning 60-65% as a good starting point to keep vibrations in the low rpm range. Thanks again; it was a good trip down engineering memory lane.
    Every so often, we get lucky. The people on this forum would be amazed at how many different organizations have used that particular formula. Have fun balancing.........

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    This is a complex subject and tecbigdogs description of balancing is correct. What is not clear is that you can reduce/shift vibrations. There are two out of balance conditions on a single cylinder engine primary and secondary imbalance forces. The primary imbalance is what is addressed by balance factor. Picture a engine with a 100% balance factor where all the reciprocating weight was used. The engine would be in balance only at TDC and BDC (more or less) but at 90 degrees to TDC/BDC would shake with the maximum out of balance force so the engine would vibrate horizontally really bad and vertically with very little energy. If the opposite were done where only the big end of the rod was counterbalanced by the counterweights (0% balance factor) then it would shake with max force vertically and very little horizontally. so a 50% balance factor would average the vibration in the horizontal and vertical directions equally and of least magnitude in any direction. Now the primary out of balance energy is created by the recriprocating weight. The less weight the less the vibrations to deal with. So one way assuming all else is equal is to reduce reciprocating weight. The out of balance energy increases exponentially with RPM. The reason for different balance factors is that as the RPM increases, the vibration energy increases as does the frequency. At certain points the frequency of the engine vibrations coincide with the frame or whatever the engine is mounted to's resonant frequency, which is where it will seem to really vibrate. By changing the balance factor you can move the vibration to a different direction either more vertical or more horizontal. The old british twins were like a big single only worse with both pistons going up and down together and the factories would use a balance factor taking into account the frame it was in. When Norton went to the commando with rubber mounted engine the balance factor went from 60 something to like 84% to move the vibrations were it would be least felt and to let the engine move in the rubber mounts most effectively. My explanation may be confusing but if anyone is really interested in this subject here is a great explaination with traces to really understand balancing at this link.
    https://www.tonyfoale.com/Articles/E...ineBalance.pdf
    One other thing is that this all assumes that the crank itself is balanced as far as the counterweights and big end go. IF you were to remove one counterweight as a drastic example now you would create a side to side imbalance which is called I think rocking couple.

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    I usually add .5 to 1 gram to reciprocating weight to allow for oil clinging to these parts while running. I found that factors as high as 72% were beneficial in some engines. My range is 56% to 72% with most in the low 60s (62-64) like stated. If you can find the shop with the capabilities, spin balancing is what I have found to be best over the parallel knife edge method. JMO. Most shops simply don't have the capabilities to properly balance a small single. I never liked using the flywheel to balance one. I prefer it to be perfectly balanced itself and add weight to the counterweights. Sorta like balancing your tires and wheels. Weights are added to the inside as well as the outside of the wheel. All the weights on one side just isn't as good. The flywheel is simply too far away from the part "out of balance" to be used to get it properly balanced. I know, I know, Ford, Dodge and Chevy did it for years but being able to add the weights to the counter weight precisely where its needed will greatly reduce torsional loads on the crankshaft. Lots of work has been done in this area recently with the big flat head singles (Kohler typically) being used in garden tractor pulling. Huge flywheels added to both ends of the crank and huge counter weights also. Good luck!

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    Wow.. Your explanation brings back some old memories. The only reason we started playing around with the balance of engines was because we had this brilliant idea that by reducing the vibrations, we could get lots more RPM's. And we actually gained about 500-800 in RPM's, but the overall cost didn't justify it. Now, if we would have walked over to the Flow Bench and spent the same amount of time on it, we probably would have accomplished the same thing and gained the same amount of RPM's (probably with less time and cost invested. Oh well..).

    Another thing you mentioned was balancing the weight between the 'Bob Weights'. We got a little lazy during our experiment and just weighted one of the Bob's. When we assembled the engine and ran it, the damn thing acted like a grasshopper and jumped all over the place. It eventually self-destructed...

    Regarding the Norton Featherbed chassis. The only problem Norton had was the rubber grommets would wear out fairly quickly because of the vibration dampening. But the bike was smooth.

    Thank you for your explanation and link. It is interesting reading.

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    I have not messed with balancing (except for wheel/tire assemblies) in a number of years.

    Back in the Flathead days, we used to balance the flywheels (as well as lighten them in the 5/12 days) to reduce vibration.

    If we had an engine with a noticeable vibration on the Dyno.....we would install a balanced flywheel and that typically cured it.

    We built a few engines where we gave the entire rotating assembly (including clutch) to the balancer, and you could pick the engine up a tenth or two from the initial build. We did not do this on the original blueprint, but waited till the engine had several build cycles on it....usually started at .020" bore at this point.

    When the Animal arrived, and we had to run the Gen1 and Gen2 flywheels we would use the Titan brand clutch (remember that drum clutches were mandatory) as this clutch had added mass for momentum, and could easily be balanced with rotating assembly instead of messing with crank and flywheel.

    When disk clutches were allowed, that went out the window so that ushered in the heavy/offset starter nut.......until the rules makers caught up, and made that impractical/impossible.

    At that point four cycle racing was dying and we switched our focus to two cycles, until the Clone came along to save/revive four-cycle karting.

    Thankfully the LO-206 does not need balancing, and Karters are embracing the platform, and we can get back to driving and having fun, and not have to worry about the engine TOO much

    Mike

    ps. I should mention one of my best friends had a Borg/Warner (maybe Stewart/Warner...can't remember) balancer and I had a dyno.....so we traded off labor to improve each of our engine programs. Never spent a penny, but spent a lot of time

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