Crank Balancing revisited

heads-a-mess, you are always good for a laugh.
Concerning the non-linear increase in force with increased RPM; If you were to graph the percent change between the two forces of an engine with an incorrect balance then you would see that the percent change between the two would be the same so that the graph would be linear. That is why I say RPM has no place in the calculations.
Here's the deal- I have done my homework and created a different way to calculate the right way to balance a 2 stroke based on my experience balancing two engines. All the naysayers and detractors have done nothing but basically express their dislike for me and negativity without having done anything other than open their big mouths.
Put up or shut up. Get off your lazy negative big rear ends and actually do something!
I applaud HS's attempt to create a machine to measure engine power. That's being creative. I like that. But if he has done nothing in the field of engine balancing then why is he making stabs at me? I can appreciate neutral criticism but not outright mean nasty dirty attacks. There is no place for that in this forum. Last I looked I thought we were all adults and not bullys in the playground.
I figured out a different way to balance the crank, a way that worked well for me. And I shared it on my site and on this forum. So why am I being attacked? Did I **** on someones gandma? No! I shared some new knowledge, that's all. I didn't know it was a sin to do that. Thing is some people hate me out of jealousy. so pathetic. grow up, people!

yes, thankyou...i made a dyno, got it finished, and then the law changed and IC is now illegal here, rendering my work pointless... such is life. its still good for the chainsaws

kitty has furballs... though kitty made the mistake of mentioning that (tony?)foale guy, quoting incorrectly, and the proof is all there earlier on in this very thread...i particularly like his use of the phrase "your theory"... i can see the implied italics

now. quick physics lessons. for those of you that dont have a library full of textbooks, well, heres a link

http://www.engineeringtoolbox.com/centripetal-acceleration-d_1285.html


for all the people that would like confirmation of this SQUARE law, and confirmation that the calculations required are NOT linear... and dont wanna use an actual calculator or pen and paper...

go down about 1/3 the page...the calculator bit.

enter 1 for mass.
enter 1 for RPM.
leave the radius at 200. can change it to one as well i guess

the answer will be 2.17 (from memory)
now, change the RPM ONLY to 2.

the answer will now be about 8N...
now change rpm to 4.

oh my....35N.


im sure, if i was to graph the results... (x1,y2.1), (x2,y8.5), (x3,y18(or so)), (x4,y35) i would end up with half a parabola... a quadratic function. maybe its a hyperbole or the other one...erm... cant think... names escaped me. anyways. the point remains standing. for every DOUBLING of RPM, centrifugal force is QUADRUPLED.

just to confirm... x8 should gimme about y70? lets go calculate!

hmmm...140. um?

oh. yeah. i only DOUBLED y...sorry.

35X4=140... now that sounds right

we can ALL make mistakes, and we can ALL admit to them at times

have fun with entering various figures into that calculator and seeing what has the biggest effect...RPM, or mass

the piston DOES experience linear acceleration... as verified mathematically, here...
http://measurespeed.com/acceleration-calculator.php


BUT...thats using the same time constant to achieve the same final speed, which is NOT what happens in reality. would REALLY reach TWICE the speed in HALF the time... so... i just made another mistake...lets recalculate

0 to 1(MPH) in 2 seconds =0.02g or 2MPS (not exactly sure what unit the m actually stands for on that page...i sorta assume miles)
(double speed, halve time)
0 to 2 in 1 second =0.09G / 4MPS
(double speed, halve time)
0 to 4 in 1/2second = 0.36G / 8MPS
(double speed, halve time)(wait...isnt 36 9x4?)
0 to 8 in 1/4 second= (its going to be BIG!) 1.45G / 16MPS... oh dear... 36x4 is pretty close to 145... 144 to be exact.

fight as hard as you can, fold the paper up, scrunch it into a ball... iunno, but there is no way those figures equate to straight lines...


dont forget the conrod, that is somewhere between the two, as it oscillates and reciprocates in a rather complex manner.

heres another link, just in case the first one one centrifugal forces was wrong...

http://www.calctool.org/CALC/phys/newtonian/centrifugal


you cannot talk knowledgeably about physics based subjects unless the information is correct. its not a personal attack, if anyone else posted the same nonsense i would say exactly the same things

the crank, conrod AND the piston share an intimate balancing act. to say ones linear (when it most definitely IS NOT) and choose to ignore the other 2/3rds of the equation is a rather poor effort, misleading at best, complete and utter rubbish at worst. its not NEW knowledge...its hocus pocus and pipedreams "my calculations dont use RPM" is one of the most foolish lines ive read in a LONG time


it makes this page look almost sensible... the third pic down gets it right, then nope...off into la la land again... despite this monumental stuff up, you still espouse your "new" pipe design as the ducks guts...http://www.dragonfly75.com/motorbike/pipes1.html

im sure im not the only member that feels this way either. just getting it out there

nasty? me? excusez moi? nope. just honest not personal.

RPM is the main factor, as it equates into the ACCELERATION of the parts in motion. to ignore it, is to cut off your nose to spite your face.

revise your mathematics, your "theory", to fit the facts and we can all sit back, nod our heads and agree for once

no jealousy at all. whats there to be jealous of? spreading misinformation as gospel truth? no, im sure you meant the lax road-rules where you live...


btw...putting lead into handlebars is nothing new i used to go the extra step and drop old carbide bits in as well... why? cus WfC has an SG of 14.3, whereas lead is a mere 11.3... ie, the carbide will sink in lead (steel floats) the joy of working in a place that had literally TONNES of the stuff in scrap alone! every courier..."what is this stuff, lead?"... "nah! heavier!"

the weight also helps on the cornering stability, as well as reducing the tendency to get the wobbles at speed by increasing the inertia in the bars... the more weight the better!


reckon i did more conclusive work just then on the "theory" of balancing than any meowing ive heard on here up to this time...



here endeth the lesson

It was a very good lesson, and once again, you can't argue with the maths.

i also had a good lesson... if one loses their post by trying to add a pic and the browser freezes, simply duplicate page! go advanced, and hey! restore auto saved content! yay!

I don't really want to get into this arguement but it got me thinking, so here's my understanding/ what I've come up with.

It includes a balance factor of 50% and doesn't include alot of factors such as the connecting rod's motion (which is rotational and reciprocal depending on where on the rod), but I think it includes enough to get the gist of it.

Obviously the effect is exaggerated because of the low numbers but you get the idea- that the side-to-side force and leftover (unbalanced) up-and-down force both increase non- linearly and both contrubute to the total vibration.



Not sure who's point it supports because there's too many to digest lol,
but it does show that the rpm has an effect on the total vibration.

Feel free to correct me on anything, all the above is just what makes sense to me and my personal understanding of the physics. I might be wrong, just tell me why

situation diffused, kinda

keatonx said:

Not sure who's point it supports because there's too many to digest lol,
but it does show that the rpm has an effect on the total vibration.

Feel free to correct me on anything, all the above is just what makes sense to me and my personal understanding of the physics. I might be wrong, just tell me why

Click to expand...

looks about right... and here in lies the reason for the lightest (least) crank weight possible. that weight cannot be balanced, and increases with RPM. in a non linear curve. the piston can only (nearly)balance in one plane...at one RPM.

light piston for speed... light crank for least vibration.

the HT uses its crank as the flywheel... heavy man


im waiting for someone to show some sense and get the HT crank, pop it in a mill and start removing material make a T crank just like on every other 2 stroke... crank stuffing? pfft. more of a detriment on these slow speed things. anyway, its worth an experiment if you want stuffing... make inserts from plastic and mount em in thin, circular steel shells that wrap around the crank halves. like this husky crank on my desk that i have to get a main bearing off of

i have a vague recollection i posted something on a thread about balancing, that the typical smartphone can be used as an accelerometer to balance engines... the link was to ducted fans... not having a smartphone...well...besides being liberated, i have to resort to other methods...such as using a friends when they arent on FB or something...


hey! he used paper! and a pen! wtf?

HeadSmess said:

i also had a good lesson... if one loses their post by trying to add a pic and the browser freezes, simply duplicate page! go advanced, and hey! restore auto saved content! yay!

Click to expand...

I'll remember that for the future, considering my computer freezes over more than my ex-girlfriend at mention that i was going to stop writing cheques to support her rampant consumerism.

I completely forgot about the increasing force that it takes to accelerate the engine+frame back and forth at higher frequencies, but according to the interwebs that relation is going to be linear (ie. If the vibrating force is doubled, the acceleration of the bike frame is also doubled).

But since the vibrating force is a parabola and the frame's absorption through inertia is linear, the vibration should still be getting stronger with rpm (not to mention moving back and forth quicker too!).

Now I know lots of engines (like my 125 2 stroke dirt bike) vibrate much less when running in their powerband. I'm gonna take a guess and say that the smoother combustion occurring at that point is the missing variable as to why some engines smooth out with rpm.

There's only one guaranteed accurate way to balance an engine properly anyways and that's with trial and error. Easiest just to go with whatever works for you lol. I had to turn all the counterweight off of the flywheel on a 160cc sachs rotary engine, to make it fit into a bike better. I'm turning up some homemade variable counterweights so I can mess with bolting on washers until I get it right

if you had a crankshaft cut from billet steel at a machine shop and tested it two turn with a weight attached representing the attachments and it will likely turn at a higher rate of rpm in tests it will like vibrate until that weight was attached to it if it was accurately high speed balanced but that all like preference if you took an assembly that was complete suspended it from the precise center and transferred that perfectly end to end each end will be centered 180 degrees apart on 360 degrees arriving at that will be less likely as easy as understanding how it could be balanced.. Yes and establishing 0 degrees on one end will help in theory 0 and 180 will be parallel or share identical center mmmmmmmk ?