These crankshaft Balancing Posts started 17th June on Page 70.
(3) What the "Balance Factor" really is.
The "Balance Factor" 45%.....50%.......60%.........85% is the portion of the "Reciprocating Mass" that is balanced by the "Counter Balance" portion of the crankshaft.
Increasing the Balance Factor increases the size (Mass) of the Counter Balance. But the Mass of the Counter Balance is always less than the weight of the Reciprocating Mass.
Here is the Balance Factor relationship defined by an equation
A = B X C ........... Counter Balance-(A) = Reciprocating Mass-(B) X Balance Factor-(C)
The counter weight only counters a % of the reciprocating weight and is lighter than the reciprocating portion of the rod/piston assembly.
As an example, a balance factor of 65% means that the counter-weight portion of the crankshaft counter weighs only 65% of the reciprocating mass of the rod/piston assembly.
The Balance Factor could be anything, 25% 48% 50..............65%......85% whatever you chose/works for that engine/frame/rev's/and everything else combo.
The counter weight portion of the crank may or may-not necessarily be dead opposite the bigend.
The Counter Balance reduces the up and down shake but increases the sideways shake. I am going to try and explain the reciprocating-mass / counter-balance / balance-factor relationship visualy using vectors.
Pic-1 The Reciprocating Mass shakes every thing up and down. And the Counter Balance shakes everything backwards and forwards. The more, the up and down shake is reduced by the Counter Balance the more the sideways back and forth shake increases.
Pic-2 Shows the Reciprocating Mass as a vector pointing up and the Counter Balance as a vector pointing across. The result of these two vector forces is the Resultant force (Z) pointing up and across at 45 degrees in Pic-2.
Pic-3 As the Balance Factor increases 45%.....50%.......60%.......... The heavier the Counter Balance becomes. And the up and down shake is reduced but the sideways back and forth shake increases. In Pic-3 you can see the up/down vector reducing and the sideways back/forward vector increasing and the resultant tipping to the right as the Balance Factor is increased.
From this I am hoping you can see that all this shaking about can be aimed and how the motor pushes and pulls against the frame can be changed.
The Balance Factor is a compromise, chose your balance factor, guess if you have to, and if it shakes the frame to much, you can change the Balance Factor to change the angle that the motor reacts with the frame.
Interestingly Phill Irving suggests a balance factor of 66% as a good place to start and the 2009 Kawasaki KX250F and KX450F (4-Stroke) Motocrossers both have Balance factors of 60%.
2009 KX250F, Engine Displacement: 249cc, Max Horsepower: 32.8 HP @ 12,200 rpm, Max Torque: 17.2 lb-ft @ 8400 rpm.
I have no real information to back this up but I think fast 2-strokes could be 50%......60%, Hard data or opinion backed by references would be welcome.
If you have a real social problem and don't get out much you can work out the magnitude of the Resultant (Z) using Vector Arithmetic.
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I ran my TF engine with only two mounts as i didn't have a bolt for the thrid yet, didn't vibrate too badly, but not exactly good.
Thanks quallman1234
On the TF crank that Team ESE is working on I was all for banging in a couple of alloy plugs like Speedpro did. Also Yow Ling was having problems with vibration in his TF. But I hear that Skunk has not had a problem with his TF in an AX frame and now I can't help wondering what sort of frame Speedpro was using.
Reminds me of Phill Irvings comments on page 107 " It is quite useless to postulate any particular balance factor as being the ideal; so many considerations enter into the matter.............................do not be misled into rebalancing your engine just because one of your pals with an entirly different machine thinks he has some magic formula"
Nearly tripped myself up, saved by Skunks post,must talk to Speedpro and find out more about why he did it, first.
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um, yeah, one is aircooled & the other watercooled, whilst the RG is kind of loosly based on the same architecture they are not the same engine by a shot. Also the running gear could not be more different.
http://www.suzukicycles.org/RG-serie...rochures.shtml
For a roadbike the safest route is a bigbore piston, should take you out to say 65cc, but you'd be lucky to find a listing, you'd have to adlib a bit but that means you'd need to take a punt & beware of different crown heights, pin positions & small end sizes (width compared to piston as well as dia) etc.
esp on a 5 speed you don't want to make it any more peaky.
Don't you look at my accountant.
He's the only one I've got.
These crankshaft Balancing Posts started 17th June on Page 70.
(3) What the "Balance Factor" really is.
The "Balance Factor" 45%.....50%.......60%.........85% is the portion of the "Reciprocating Mass" that is balanced by the "Counter Balance", heavy side of the crankshaft.
(4) I will answer this question, Which is heavier, (A) the reciprocating weight of the rod piston assembly or (B) the counter weight of the crankshaft.
The counter weight only counters a % of the reciprocating weight and is always lighter than the reciprocating portion of the rod/piston assembly.
As an example, a balance factor of 65% means that the counter-weight portion of the crankshaft counter weighs only 65% of the reciprocating mass of the rod/piston assembly.
(5) Why there is a "Balance Factor" and what changing it does.
The Counter Balance reduces the up and down shake but increases the sideways shake. You have to make a compromise, a 100% up and down shake balanced out becomes a 100% sideways shake.
The compromise is the Balance Factor. The down side is that the Balance Factor is only good for a narrow rev range. The up side is that you can tweak the Balance Factor to aim the out of balance vibrations into the strong/heavy part of the frame. The Balance Factor can also be tweaked to move vibration to another part of the rev range that you don't use much.
Pic-1 on some cranks you can't see the counterbalance, you just have to imagine its there. On the cranks in Pic-1 the counterbalance (heavy side) is created by drilling holes near the crank pin.
Pic-2 you can see the cranks have different balance factors and the crank in Pic-1 has different size holes either side of the bigend this offsets the counterbalance as drawn in Pic-3.
Pic-3 shows that some cranks do not have the counter balance opposite the bigend. An example is the TF crank in Pic-1.
Pic-4 Thomas is holding a card showing how the angle of vibration changes with changes in balance factor. You can also tweak the balance factor to move a rough vibration patch away from a critical RPM.
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The percentages quoted are "mass".
The forces generated by the reciprocating mass increases linearly as a function of the rate of reciprocating.
The force generated by the rotating mass increases as a square of the rate of rotating.
Therefore, even though at standstill the rotating mass only exerts a force equal to say 60% of that exerted by the mass of the reciprocating parts, as the engine speed increases the forces generated by the rotating parts increases at a greater and greater rate and eventually equals the force being generated by the reciprocating parts. If engine speed continues to increase the forces generated by the rotating parts will exceed the forces generated by the reciprocating parts. The forces mathematically only equal each other at a single engine speed. We want that speed to be close to the operating speed.
On a single the forces at 90deg to the cylinder bore are unopposed regardless of the % used as there is no force generated by reciprocating parts to oppose them. 90deg V-twins are wonderful.
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Thanks Speedpro, that explains it very well, I was struggling to paint the picture.
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These crankshaft Balancing Posts started 17th June on Page 70.
(6) What to do with your "Balance Factor"
Pic-1 Find the weight of you're Reciprocating Mass.
Pic-2 For a Balance Factor of 55% say. Weigh out some washers untill you have a pile of them that weigh 55% or 0.55 X Reciprocating Mass.
Pic-3 Attach the washers to the end of the con-rod. Don't forget to include the weight of the cable tie.
You can reverse engineer this to find the balance factor of an existing crank.
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These crankshaft Balancing Posts started 17th June on Page 70.
(7) A simple but very effective jig for statically balancing a crank, that you can make yourself in 10min's. (Thanks Thomas)
Pic-1 Thomas showing of the balancing jig he lashed up in about 10mins.
Pic-2 The tubes act like a knife edges and are a very frictionless surface for the crank to roll on. The tubes are the key to the whole thing.
Pic-3 Nothing has to be flash. The only criteria is that its level and the tubes are parallel.
From Phill Irving. page 109 "the wheels will roll freely along the straight-edges and show no tendency to settle in any one position; if not, the pin will go to the top or bottom according to whether the Counter Balance is to heavy or to light. Correction is usually made by drilling the rims."
There you have it, the KISS method of re-balancing a single cylinder 2 or 4-stroke.
Very simple, very effective, a very accurate way to balance a single cylinder crankshaft staticaly. If anyone can come up with a better static balancing method, Thomas would like to hear about it.
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Re-Engineering to find the Balance Factor of a CrankShaft.
Pic-1 Hang things of the little end untill.............
Pic-2 ...........the crank no longer rolls and stays in whatever position it's placed.
Pic-3 Weigh the washers and the little end.
Pic-4 Weigh the Reciprocating Mass.
Divide the Weight of the Washers + weight of the Little End by the Weight of the Reciprocating Mass and there you have the Balance Factor.
Rearanging the formula I posted earlier.
Let:- "Washers"+"Little end" = A "Reciprocating Mass" = B and "Balance Factor" = C
Then Balance Factor C = A/B .............."Weight of the Washers"+"Weight of Little End"/"Weight of the Reciprocating Mass"
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