I'm putting this is General as this would apply to all models of Big Twin motors, as well as Sportsters.
Rather than add a lot of traffic to another posting in Twin Cam, I decided to make a new post.
I'm using the S&S balance work sheet as it best defines what is measured and what the weights that need to be added to each flywheel to balance each one. The reason for the post is to see how much difference in balance factor a change in piston weight has on the crankshaft.
The sheet is using basic Evo motor component weights. And then gives the weight that is needed to attach to each flywheel to balance them statically. Then I added another column with piston weight changes to see the effect on balance factor.
The jest of the sheet shows that with pistons weighing 1230 grams (both pistons) to reach a balance factor of 60% we need to add 1273.9 grams of bobweight to each flywheel so it can be balanced. Then by changing the piston weights to 1118 grams (both pistons) and we add the same bobweight value of 1273.9 grams, the balance factor is now 64%.
I'm pretty sure this is accurate because the rods, crankpin, etc. weights are irrelevant if we don't change them. We're looking for a balance factor and what weight is needed to reach that.
Anyone that's balanced HD cranks, I welcome your feedback to see if you agree with this.
crank balance sheet 01.jpg
I think what you're asking is correct.
I trued & balanced my own flywheels for years. I still have the S&S balancing kit & an old Harley truing stand & a digital scale (& a Snap-On TQ multiplier I used to tighten down the crankpins) We used a 60% balance factor on almost everything.
I haven't used the stuff in years & just keep it around for nostalgia reasons. Years ago, I was half owner of a custom Harley chopper shop (my partner who is dead now was an H.A. member) & I did all the flywheel truing & balancing for tons of stroker motors we built back then.
~John
Quote from: Ohio HD on February 04, 2022, 01:53:50 AMI'm putting this is General as this would apply to all models of Big Twin motors, as well as Sportsters.
Rather than add a lot of traffic to another posting in Twin Cam, I decided to make a new post.
I'm using the S&S balance work sheet as it best defines what is measured and what the weights that need to be added to each flywheel to balance each one. The reason for the post is to see how much difference in balance factor a change in piston weight has on the crankshaft.
The sheet is using basic Evo motor component weights. And then gives the weight that is needed to attach to each flywheel to balance them statically. Then I added another column with piston weight changes to see the effect on balance factor.
The jest of the sheet shows that with pistons weighing 1230 grams (both pistons) to reach a balance factor of 60% we need to add 1273.9 grams of bobweight to each flywheel so it can be balanced. Then by changing the piston weights to 1118 grams (both pistons) and we add the same bobweight value of 1273.9 grams, the balance factor is now 64%.
I'm pretty sure this is accurate because the rods, crankpin, etc. weights are irrelevant if we don't change them. We're looking for a balance factor and what weight is needed to reach that.
Anyone that's balanced HD cranks, I welcome your feedback to see if you agree with this.
crank balance sheet 01.jpg
Another way to examine this is to run the numbers for piston A to achieve a balance factor of X. Then change the piston weights and do a reverse calculation. What you should see is something like piston A = X% balance factor. Pistons B have a balance factor of Y% using the same crank and the delta is Z%. This is used often during rebuilds to determine if a re-balance is required.
Thanks, I was brain locked on reversing the calculation, you made me look at it again. I think I have it correct.
crank balance sheet 02.jpg
Brian, I'm a little confused by a couple of numbers on the balancing example that you posted. On the left side under CP it reads 421. On the right side under the front piston weight column it reads 470. Please ignore my ignorance but what does the 421 denote? This is the figure that shows as piston weight on the spec sheet. Perhaps I'm missing something and it is actually 470?
Bill, no your not missing anything. The 470 was a weight for any standard piston. I was just trying to get the calculation to give me a 60% balance factor. Then the 421 was just a note for me (your CP piston weight) and the 559 is your total weight based on what you measured. The 615 across from the 559 is the other piston weight total.
The whole exercise was for me to determine what a piston weight change would do to a given 60% balance factor. It doesn't matter what V-twin motor it is once you have some established values. And only change the relevant piston weight. I wanted to use the S&S weight of 1230 for two early TC piston weights to establish the 60% factor.
Turboprop jogged my brain and I created the second calculation, only seeing what the piston weight does to an established 60% factor. All of the other calculations on the first sheet are to come up with bobweight values to actually allow you to balance the flywheel halves. The piston weight is of course a part of that.
Don mentioned earlier that CP may be able to supply a heavier wrist pin for your pistons. That's why I mentioned to weigh the original piston, rings, etc. to see what you really have. Those two weights are really the only two values that you can calculate what you may need to do. See what the difference really is. Remember that your piston will weigh a little less when they come back from Fuel Moto.
Brian,,
OK, I see now. Obviously best to try to ring that balance factor back down closer to 60%. Campbell Industries opens in about another 40 minutes (weather permitting). I may give them a ring and ask about heavier wrist pins.
Much appreciate your and Turboprop's time, Bill
So you are going to balance the crank at 60%? On a rubber mount I'd do around 52. 60% is good for a solid mount un-counter balanced motor as it directs some of the vibes horizontally.
No, no balancing going on. I'm just looking to see what effect piston weight changes have on an existing balance factor.
I used to use the DOS version of Accelerator Dyno program, it had the crank balance program in it. I don't have a PC that'll run a DOS program anymore.
The numbers you have are correct then.
Old BF x Old Recip
New BF = ------------------------
New Recip
Note that for me the rod ends weighed 227 front 248 rear 2000 TC crank.
Thanks, I appreciate your input on the calculation.
I used Evo component info just to get a balance factor. I don't have the weights of TC crank components.
I understand.. Just providing more info..
Also, Stock 2000 fxdx crank looks to be balanced at 52%. At least that is what I got.
Brian and Don @ HD Street Performance,
Max asked a balance/weight question on the TC page on the CP 98" piston thread that I started. He noted that
even with the 131 gram wrist pins we're still 43 grams shy of the 600 gram weight of the stock piston assembly. I replied with a question that probably belongs on this thread so I'll ask it here. I found some .927 X 2.250 wrist pins on the Summit Racing site that are .250 wall thickness and weight 153 grams each. They are Diamond brand and made out of H-13 tool steel. With reference to Max's question about stock 88" piston weight I wondered if the heavier wrist pins would put me closer to stock balance? Thanks, Bill
Bill, I agree with Max. The 0.200 wall pins are not going to equal the weight of 600 grams per piston. Below is what I get, it matches what Max said. I also calculated the 0.250 wall pin area and come up very close to what they told you, a weight of 153 (I got 155.237). This gets you close to the 600 gram weight.
p1.jpg
p2.jpg
Then I used a 52% balance factor supplied by Max as a known early TC balance factor of a 2000 FXDX
With the 0.250 wall pins the balance factor goes to 53.3%. This should be just fine with the 0.250" wall pins then.
I still would like you to weigh the old pistons and rings so that you know what you really have. We're relying on a 600 gram piston weight as a standard. It would be good to know what the old pistons assemblies weighed.
b1.jpg
Good work & interesting Thank you
Brian, Thanks for your time plugging in these figures and helping me to understand balance factors and thanks to Max for his keen eye. Just for clarification, you're talking the original 88" pistons, pins, keepers and rings, not the RevPerfs, correct? I will try to find a more accurate scale to firm up the weight of those pistons. Your help is greatly appreciated.
Bill, if you are going through the trouble to reweigh one set on a known accurate scale, I would weigh both complete sets (as is) so you know what you have and how to get where (or close) to where you want to be.
Bruce if we are to ignore the factories balance factor what do you think is an appropriate factor for a street performance Twin Cam?
Quote from: billbuilds on February 06, 2022, 06:46:34 AMBrian, Thanks for your time plugging in these figures and helping me to understand balance factors and thanks to Max for his keen eye. Just for clarification, you're talking the original 88" pistons, pins, keepers and rings, not the RevPerfs, correct? I will try to find a more accurate scale to firm up the weight of those pistons. Your help is greatly appreciated.
No problem at all. It's been a good learning process along the way. And Max added some good info for us as well.
Yes, the 88" parts. Just to be certain is all. It's one of things that would keep me up at night because I didn't know. :teeth:
And as Kirk stated, if possible weigh the new set when you get them back, just to be certain.
Kirk and Brian,
I've been having a difficult time coming up with an accurate scale to use but luck may have changed. I'm seeing a triple beam balance scale for sale on Craigslist that's about a forty-five minute drive from me. Still has box and instructions and looks pretty much new. The guy is only looking for $50. Would a scale such as this be satisfactory for measuring the weight of these pistons? They have digital kitchen scales at Walmart but I don't really trust their accuracy. Thanks, Bill
If the triple beam is in good shape and a quality brand, it's going to be very accurate.
It's an Ohaus brand with a 2610 gram limit. There are quite a few on ebay so seems his asking price is pretty fair.
Thanks for the quick reply, Bill
Ohause is a great brand. I'd buy it. I used to have one a long time ago.
With a beam scale you can confirm the accuracy with weights in / on the pan. The beam will have an adjustment to set 0 and in some cases you can add things like lead shot to. Most producers of beam scales aim for accuracy and a good name brand usually won't risk their reputation with crap. You may be able to take it in to a gold buyer or like business and check it against or with test weights. Once done it will be good to go provided the knife edges and pivot load bearing surfaces are protected in transport and handling. IMO They are a good choice because they don't depend on things like battery power level.
As far as the electric, battery powered, mine shows when low battery, and it shouldn't be used at that point until new batteries are put in the unit. You can buy an AC power supply for it.
My standard is a CP piston. If it reads what CP says in the documentation, then it's correct. It always has matched their piston weight.
Triple check ever thing with three scales, one triple beam two digital. Also made a jig for weighing both ends of rods the same time. All three end up reading the same.
Quote from: Buglet on February 07, 2022, 11:05:16 AMTriple check ever thing with three scales, one triple beam two digital. Also made a jig for weighing both ends of rods the same time. All three end up reading the same.
Got a pick of that setup? Sounds interesting.
The scale I picked up has a 610 gram limit as is. I'd have to add a weight to the bar for an additional 2000 grams of capacity. It came in the box with instructions and even had the cardboard to hold the bar in place for safe transport. There's a knob under the plate to zero out the balance.
I didn't mark the pistons for position when I removed them. With wrist pin, pin retainer clips and rings included piston #1 weighs 596.2 grams. With pins, clips and rings included piston #2 weighs 600.1 grams. Is it pretty normal for stock pistons to be off a bit in weight like this?
Does one have more carbon that the other?
They should weigh the same, front and rear are the same piston. But, it's only 3.8 grams, or 0.13 ounces. You would just use the total anyway when balancing a crank.
I am just wondering now what is the goal? Changing or duplicating the factories correction factor? If so to what. which was the reason for my last question. And besides balancing what about added weight up top and stress on other components. This tractor motor is now being asked to dance a little.
This is am interesting article on the topic LINK (https://www.hydra-glide.net/joomla/index.php/documentation/miscellaneous/1145-balancing)
Brian,
I cleaned the carbon off both pretty thoroughly. I did clean all parts of the lighter of the two in Dawn dish washing liquid. Wasn't sure if it made a signficant difference so I hadn't bothered with the other. I'll do the same to it in the AM and report back. Thanks
Don, You obviously feel that the 131 gram wrist pin will be adequate. Max, it'd be great if you would chime in with your take on this. Thanks, Bill
Bill I plugged in the two values you have as OEM numbers.
If the OEM balance is 52%, then this only pushes the needle to 53.2%. I wouldn't be loosing sleep over it.
using 153 gram pins
b3.jpg
Brian,
I removed the rings, pin and clips on the heavier piston assembly and cleaned them all. The bare pistons do weigh slightly different: 415.5 grams and 419.15 grams. The pins are only different by .02 gram (143.6 and 143.62). There's maybe a .01 gram difference between one ring and clip set and the other. I bet that the CP pistons will be closer in weight than the stock ones are after Jamie machines the domes.
Once again I really appreciate your help figuring the balance equation. This was a great learning experience for me. :up: Bill
Ohio I have no pictures and it's pack away as it's not used to often anymore. The first chance I get I pull it out and get some pictures in the next week or two. All I can say it's a time saver.
"Don, You obviously feel that the 131 gram wrist pin will be adequate. Max, it'd be great if you would chime in with your take on this. Thanks, Bill"
Not really I just am taking a little higher level view of the situation and wondering what the goal is? Given the availability of pin weights there is some flexibility to change the balance factor without machine work. Once a balance factor is decided then the right pin weight can be decided.
Don,
It's my understanding that we were trying to maintain the stock balance factor of 52%. I am not real knowledgable in this area so I have to try to learn from others. I like to think that I'm still teachable but of course I'm biased.
It was suggested that I weigh the stock pistons, pins, clips and rings. It's my understaanding that to maintain the stock "factory" balance the new pistons, pins clips and rings should be as close to their stock counterparts weight as possible.
I really appreciate you mentioning the probable need for heavier wrist pins to make up for the weight lost in machining off the 10.4cc domes. What I don't understand is why you feel that a new piston/pin, etc. combo that is the same weight as the stock ones is going to create more stress on the motor. Thanks for posting the link to the balancing article. Ideally I'd ship the crank off to Darkhorse but that is not in the budget. Bill
Don What do you think would be the right balance factor should be for this set up.
Bill, this is one mans opinion, Bob Behn of RB Racing.
I think the range he speaks about is where you want to be 52% to 55%
RB Racing (https://www.rbracing-rsr.com/balance2.html)
:up: Bob is a smart guy. He is one of those people that knows from experience and is worth listening to. He's a leader in many areas in the M/C world. He sometimes is gruff and more to the point than many care for, but .... :nix:
Yeah, the phone conversations I've had really just made me smile as he cussed up a storm. I like the guy.
Bill I think you are on the right path.
Quote from: HD Street Performance on February 06, 2022, 09:25:33 AMBruce if we are to ignore the factories balance factor what do you think is an appropriate factor for a street performance Twin Cam?
Don't really know.. Looks like Ohio got an answer from RB racing. It's probably good. I will say that after going from 600 gram piston assys to 525 gram on my 131, I started to snap of exhaust header studs. Replacing the crank with one balanced to the lighter pistons cut the vibes by quite a bit.
I would think that 52-55 (what Ohio got from RB) would be good for a rubber mount.
While this guy don't show all his work when going to a V twin, he does a fair job of showing what goes on with different balance factors.
http://www.brufnut.de/SS100/ENGINE/CRANK_BALANCE/crank_balance.htm
The math he shows is the initial calcs for piston position (same as what's in the CCP calculator spreadsheet). If you click on that sheet he show the derivation for forces for a single reciprocating piston. All you have to do is take the results, convert it to a vector for each piston and crunch the numbers.. :D
It's interesting that rod to stoke ratio plays a big factor in what the balance factor should be.
Thanks for the replies and the links. Your help is what continues to make this a great site. :up: Bill
Quote from: Admiral Akbar on February 04, 2022, 09:37:43 AMThe numbers you have are correct then.
Old BF x Old Recip
New BF = ------------------------
New Recip
Note that for me the rod ends weighed 227 front 248 rear 2000 TC crank.
This is the much less convoluted calculation that Max expressed, and I think what Turboprop was pointing me to.
This is when replacing piston weights, an easy calculation.
b4.jpg
This an example of dynamic balancing an HD crankshaft with an older Stewart Warner crankshaft balancer.
The shop is Truett and Osborn
The last time I was out to S&S they balance there flywheels with the rods on it all one assembly. It would spin the wheels and drill the holes all in one process, all automatic. No taking the wheels apart and putting them back together.
Many times Truett and Osborn is selling the flywheels to a dealer that's building the motor. Dealer gives T&O the crank pin, rod and piston weights. Then T&O balances the wheels for the customer. S&S also observes this practice if a dealer asks.
Note that in the T&O video it's not a TC motor.
Just to add a balance factor that will be in use soon. I'm having a crank built by Darkhorse for a 124" Twin Cam. This is a 4-5/8 stroke crank. I just asked Andrew what the balance factor will be, as I of course am leaving it up to them to decide that. He said 54% is what it'll be balanced to.
This is a Twin Cam 'A' motor. It's a street motor, and I assume he used the input from me that it'll operate 85% of the time in the 2,500 to 4,500 rpm range. Face it, unless you're strictly building a motor to race, or spend all day lugging your motor, that's where you ride 85% of the time.
Good to know, thanks for posting and yes, at least for me, you're right about RPM range.
Quote from: Ohio HD on February 14, 2022, 01:48:45 PMJust to add a balance factor that will be in use soon. I'm having a crank built by Darkhorse for a 124" Twin Cam. This is a 4-5/8 stroke crank. I just asked Andrew what the balance factor will be, as I of course am leaving it up to them to decide that. He said 54% is what it'll be balanced to.
This is a Twin Cam 'A' motor. It's a street motor, and I assume he used the input from me that it'll operate 85% of the time in the 2,500 to 4,500 rpm range. Face it, unless you're strictly building a motor to race, or spend all day lugging your motor, that's where you ride 85% of the time.
While 54% seems like a reasonable number you bring up an interesting issue that has always bothered me.. When you have a physical imbalance, it seems to me that the force of the imbalance increases with RPM no mater what. In other words, how to you balance a motor for a specific RPM? It seem to me that setting balance factor would have to include the system as a whole.. In other words, balance factor would need to include the whole motorcycle with all it's masses, rubberized mounts and other flexing. In that case, the balance could be used to minimize vibrations as a system.
One thing I thought was interesting was that John Dahmer mentioned that they look at compression ration when selecting balance factor in a discussion about cranks with Kevin Baxter on Utube.
From the link I posted in an earlier message, I can see that the analysis, says rod to stroke ratio is important. On HDs it changes with the increase of stroke since rod length stays the same..
Interesting stuff but I do wonder how much of the stuff is anecdotal base on certain experiences and how much is done through the latest available engineering techniques / simulations.
Quote from: Admiral Akbar on February 15, 2022, 09:59:21 AMQuote from: Ohio HD on February 14, 2022, 01:48:45 PMJust to add a balance factor that will be in use soon. I'm having a crank built by Darkhorse for a 124" Twin Cam. This is a 4-5/8 stroke crank. I just asked Andrew what the balance factor will be, as I of course am leaving it up to them to decide that. He said 54% is what it'll be balanced to.
This is a Twin Cam 'A' motor. It's a street motor, and I assume he used the input from me that it'll operate 85% of the time in the 2,500 to 4,500 rpm range. Face it, unless you're strictly building a motor to race, or spend all day lugging your motor, that's where you ride 85% of the time.
While 54% seems like a reasonable number you bring up an interesting issue that has always bothered me.. When you have a physical imbalance, it seems to me that the force of the imbalance increases with RPM no mater what. In other words, how to you balance a motor for a specific RPM? It seem to me that setting balance factor would have to include the system as a whole.. In other words, balance factor would need to include the whole motorcycle with all it's masses, rubberized mounts and other flexing. In that case, the balance could be used to minimize vibrations as a system.
One thing I thought was interesting was that John Dahmer mentioned that they look at compression ration when selecting balance factor in a discussion about cranks with Kevin Baxter on Utube.
From the link I posted in an earlier message, I can see that the analysis, says rod to stroke ratio is important. On HDs it changes with the increase of stroke since rod length stays the same..
Interesting stuff but I do wonder how much of the stuff is anecdotal base on certain experiences and how much is done through the latest available engineering techniques / simulations.
I watched that Youtube video a while back. I also thought about the compression, and wonder what part it plays in the decision. I would have liked to ask a lot of questions of Andrew, but I know they're really busy.
Below is the information that I sent. They do have compression on the list of info they request.
balance DH.jpg
Quote from: Admiral Akbar on February 15, 2022, 09:59:21 AMQuote from: Ohio HD on February 14, 2022, 01:48:45 PMJust to add a balance factor that will be in use soon. I'm having a crank built by Darkhorse for a 124" Twin Cam. This is a 4-5/8 stroke crank. I just asked Andrew what the balance factor will be, as I of course am leaving it up to them to decide that. He said 54% is what it'll be balanced to.
This is a Twin Cam 'A' motor. It's a street motor, and I assume he used the input from me that it'll operate 85% of the time in the 2,500 to 4,500 rpm range. Face it, unless you're strictly building a motor to race, or spend all day lugging your motor, that's where you ride 85% of the time.
While 54% seems like a reasonable number you bring up an interesting issue that has always bothered me.. When you have a physical imbalance, it seems to me that the force of the imbalance increases with RPM no mater what. In other words, how to you balance a motor for a specific RPM? It seem to me that setting balance factor would have to include the system as a whole.. In other words, balance factor would need to include the whole motorcycle with all it's masses, rubberized mounts and other flexing. In that case, the balance could be used to minimize vibrations as a system.
One thing I thought was interesting was that John Dahmer mentioned that they look at compression ration when selecting balance factor in a discussion about cranks with Kevin Baxter on Utube.
From the link I posted in an earlier message, I can see that the analysis, says rod to stroke ratio is important. On HDs it changes with the increase of stroke since rod length stays the same..
Interesting stuff but I do wonder how much of the stuff is anecdotal base on certain experiences and how much is done through the latest available engineering techniques / simulations.
This is a great conversation. Here's thought or two.
The force of imbalance can be equally influenced by the effect of underweight components swinging around the crank. As the rpm increases the underweight bob weight if you mant, increases it's effect and may smooth out. This could explain the way the balance factor is more rpm dependent.
More compression will drive a weight harder (or less as it may be related to compression, cam timing effects on compression and rpm / intake flow characteristics as efficiencies) and therefore change it's relationship to the crank and rpm will again influence the rate or amount of how that effect is distributed throughout the rpm range. I see more than bob weight being the influencer of vibration and it's position in the rpm range. That may be the consideration for John and Baxter too. I notice compression and cam ID is part of the DH balance spec sheet.
I believe in many ways anecdotal findings are required to and do prove results taken from any available engineering techniques and simulations. Is that not how these engineering formulas evolve as useful calculations?
To be clear, I don't have the big Eng. ring or any where near the experience of those being referenced or contributing here. I do usually have a decent grasp on physics in ICE's and strive to keep it simple. These are my thoughts only after listening to the more respected input in the previous posts.
Quote from: kd on February 15, 2022, 10:51:03 AM[Snipped to shorten]
This is a great conversation. Here's thought or two.
The force of imbalance can be equally influenced by the effect of underweight components swinging around the crank. As the rpm increases the underweight bob weight if you mant, increases it's effect and may smooth out. This could explain the way the balance factor is more rpm dependent.
More compression will drive a weight harder (or less as it may be related to compression, cam timing effects on compression and rpm / intake flow characteristics as efficiencies) and therefore change it's relationship to the crank and rpm will again influence the rate or amount of how that effect is distributed throughout the rpm range. I see more than bob weight being the influencer of vibration and it's position in the rpm range. That may be the consideration for John and Baxter too. I notice compression and cam ID is part of the DH balance spec sheet.
I believe in many ways anecdotal findings are required to and do prove results taken from any available engineering techniques and simulations. Is that not how these engineering formulas evolve as useful calculations?
To be clear, I don't have the big Eng. ring or any where near the experience of those being referenced or contributing here. I do usually have a decent grasp on physics in ICE's and strive to keep it simple. These are my thoughts only after listening to the more respected input in the previous posts.
Believe me when I say most of my calculus skills are gone and physics is not much better so I have to rely on someone else coming up with the correct answer.
Here is where the guys does the calcs for acceleration of the reciprocating weight at the bottom.
http://www.brufnut.de/SS100/ENGINE/CRANK_BALANCE/Balance_6a.gif
So the net forces are nothing more than F = M x A for the Recip and it's pretty much the same for a rotational force.
If you look at his equation its,
A = Stroke x (2 x pi x RPMs) squared x (a bunch of stuff related to position of the recip mas).
So the resultant force is
F = M x Stroke x (2 x pi x RPMs) squared x (a bunch of stuff related to position of the recip mas).
The centripetal force is
F = M x R x (2 x pi x RPMs) squared.
Notice that the magnitude of the force changes in both cases by square of the RPMs in both cases. That seems to to tell me that as RPMs go up, so does the vibration. There isn't a sweet spot where the forces reduce.
I do think you bring up a point. With a higher compression motor, the flywheel is going to accelerate more on the power stroke and slow down more on the compression stroke. While the motors RPM may be say 4500 average, is the down stroke the equivalent of say 4700 at the start and the up stroke the equivalent of say 4300 RPM at the end.. Does that upset the overall balance?
Anecdotal evidence really leads to the engineering calculations and experimentation validate the calculations..
You a ring when you become an engineer? I got gypped.
Notice that the magnitude of the force changes in both cases by square of the RPMs in both cases. That seems to to tell me that as RPMs go up, so does the vibration. There isn't a sweet spot where the forces reduce.
With the calculation it does appear the vibration will increase with rpm and I agree with that theory. It must be supported in truth or it wouldn't be used. I agree the force should increase with rpm. My comment on this is, if the counter weight is not enough it will cause it to vibrate also? If so, as the rpm increases, the reciprocating force should increase and enter period where it becomes more happy and smooths out. I can also see how it could pass through the sweet spot and possibly start to vibrate again. If so, is that the reason the selected designed in balance factor (that 50 to 60 percent) changes for engines intended to be used at different rpm ranges?
(The example would be in this conversation with the 45 degree twin, the factor has been between 50% and 60%. The criteria seems to be the intended operating rpm. I expect the confused firing and exhaust with the 45 degree engine may have something to do with all of this too. It is hard to know when you can get too far into the weeds with details that have little or no effect on the balance and what part of the vibration is from the unconventional / unorganized firing / exhaust cycles and out of our control to correct.)
I have always noticed at the lower rpm there seems to be a spot around say 2500 rpm, where you can feel the power stroke vibration no matter what the engine configuration is. With more cylinders it doesn't seem so noticeable in vibration but still seems detectible in the exhaust note. For all I know, that could be most cam design are set for torque output (to help the engine get the mass into rotation) and the subsequent cylinder feed at work producing harder combustion. Even if that is so, why? More compression due to cam design? Is there a lighter reciprocating weight causing imbalance because it is where the balance factor should be higher or lower? Does it smooth out because of the influence of your calculation example being speed sensitive or the changes in cam efficiency effecting compression? Will it pass through that sweet spot and enter a new vibration period at the top rpm?.
:scratch: You didn't get a ring? :nix:
QuoteIf so, as the rpm increases, the reciprocating force should increase and enter period where it becomes more happy and smooths out.
I think you are missing my point. The reciprocating forces increase at the same rate as the counter balance rate. None of it ever cancels out. They grow together as the Rs go up.
What is interesting is that more the cylinders to 90 deg and most of the imbalance goes away. (see the link I posted) IIRC the Vrod was at 70 deg and still used a counter balancer. There are second order vibes but they are typically much less than the first order ones.
The stuff you feel at 2500 is the acceleration of rotation of the crank running to the rear wheel. The compensator helps to get rid of it..
They did mail me a fancy piece of paper..
you're right, I did miss your point. Got it now and agree with that.
I am aware of the crank and firing resonance / compensator buffering. I have also noticed it even on v 8 engines. As I said, more so in the exhaust note that all engines seem to have in that range. To me anyway. I just threw that in there because I always wondered if it was relevant to balance factor.
Keep that paper out of the sun or behind laminated glass to stop it from fading away. You don't want to lose the ability to think. :wink: