ESE's works engine tuner

[SwePatrick]

Andreas, Look at it simple..
You need the inertia(weight) to balance the cranks inertia.
No way around it, if you want to use a small diameter balanceshaft, it needs to be longer to reach the same inertia.
You need the mass in some configuration, and thereby you won´t gain any response however you do it.
Oh,, well one way it might be useful with a small diam, that would be the windage and hitting the oil should be less.

[andreas]

Andreas, Look at it simple..
You need the inertia(weight) to balance the cranks inertia.
No way around it, if you want to use a small diameter balanceshaft, it needs to be longer to reach the same inertia.
You need the mass in some configuration, and thereby you won´t gain any response however you do it.
Oh,, well one way it might be useful with a small diam, that would be the windage and hitting the oil should be less.

Yes, it might be a brain ghost after all. By the way I've seen your external dito, rather like it.

[Muhr]

Yes, it might be a brain ghost after all. By the way I've seen your external dito, rather like it.

centrifugal force is not linear in a given direction with different centers of mass so I would never leave stroke length with center of balance mass on a balance shaft.

[andreas]

Sorry aint got no cad, and don't wish to hijack the thread, but here is the straightforeward.

[SwePatrick]

Yes, the weight 180 degree from 'no weight' will have the most inertia, but.....

[andreas]

The efficacy of a balance shaft is dependant upon two factors = m x r.
If you take the whole mass as being at a single point then that mass at the radius squared is the rotational inertia.
In the diagram it would appear that the bottom shaft has more eccentric mass within the same outer radius , thus will
have more rotational ineria effect.

That's what I mean, instead of a half circle, you conentrate the mass closest possible to this single point- and loose some momentum. Or what am I missing.

[wobbly]

Here we are talking about two differing effects.
Rotational inertia is scalar - that is it has no directional vector , the larger the mass or the bigger the effective radius then the inertia
number gets larger.
Balance forces are a vector , that is a force created by the eccentric mass has a directional value about the center of rotation.
Thus whenver the balance factor is increased , by more mass added opposite the crank pin , then this added mass will increase the
rotaional inertia that has to be accelerated.
But , here is the kicker - reducing rotational inertia of a 2T crank can be counterproductive.
The lower value of inertia allows the crank to accelerate faster away from TDC due to the gas pressure of combustion.
This faster acceleration results in faster velocity thru BDC.
This effectively reduces the STA of the transfers, and in practice the effect is seen as a lack of overev power.
I first discovered this on a TM125MX , when I took off the ignition rotor and replaced it with just a timing disk.
The engine , that previously spun to well over 13,000 easily, now would not go past 12,000.
Later I discoverd that VHM and Honda both produced higher inertia cranks to be used with no flywheel when converting to total loss.
In our discussion of balance shafts the added inertia may in fact produce better performance due to the above effect.
But - the added inertia may also overcome any added porformace simply due to the extra power absorbed trying to accelerate the added mass.
How much inertia is too much ? - look at an Aprilia crank with many inserts of tungsten close to the outside of the crank discs.
That may be the optimum balance between acceleration rate - Vs overev power.
I think it was Doc Fleck at Queens that first documented this behavour - noting that a heavyer dyno flywheel appeared to make the engine
being tested to create more top end Hp by slowing down the " in cycle speed variation " behavour.

[andreas]

Here we are talking about two differing effects.
Rotational inertia is scalar - that is it has no directional vector , the larger the mass or the bigger the effective radius then the inertia
number gets larger.
Balance forces are a vector , that is a force created by the eccentric mass has a directional value about the center of rotation.
Thus whenver the balance factor is increased , by more mass added opposite the crank pin , then this added mass will increase the
rotaional inertia that has to be accelerated.
But , here is the kicker - reducing rotational inertia of a 2T crank can be counterproductive.
The lower value of inertia allows the crank to accelerate faster away from TDC due to the gas pressure of combustion.
This faster acceleration results in faster velocity thru BDC.
This effectively reduces the STA of the transfers, and in practice the effect is seen as a lack of overev power.
I first discovered this on a TM125MX , when I took off the ignition rotor and replaced it with just a timing disk.
The engine , that previously spun to well over 13,000 easily, now would not go past 12,000.
Later I discoverd that VHM and Honda both produced higher inertia cranks to be used with no flywheel when converting to total loss.
In our discussion of balance shafts the added inertia may in fact produce better performance due to the above effect.
But - the added inertia may also overcome any added porformace simply due to the extra power absorbed trying to accelerate the added mass.
How much inertia is too much ? - look at an Aprilia crank with many inserts of tungsten close to the outside of the crank discs.
That may be the optimum balance between acceleration rate - Vs overev power.
I think it was Doc Fleck at Queens that first documented this behavour - noting that a heavyer dyno flywheel appeared to make the engine
being tested to create more top end Hp by slowing down the " in cycle speed variation " behavour.

Highly interesting, thank Wobbly.

[Frits Overmars]

Balance shafts can eliminate the shake altogether

Yep - if we employ two balance shafts per crankshaft, or the Husaberg-solution with balance weights on the crankshaft.
In our usual layouts there is a definite distance between crankshaft and balance shaft. This distance between a crank force acting in one direction and a balance force acting in the opposite direction causes a fore-aft rocking torque.
The balance shaft solution as used in the Aprilia RSA for example, with outrigger balance masses, allows the smallest distance between crankshaft and balance shaft center lines.
In the Husaberg approach this distance is zero, which in itself is perfect. But if you want to do this right, you'll need balance discs on both sides of the crankshaft and both these discs must rotate counter-crankshaft-wise, which will require a handful of gears.

[SwePatrick]

When talking balanceshafts, i now run a verion in my engine like the aprilia type.
One weight on each side of crank as close as possible to the center och the crankshaft.

Is there any data recorded with or without balancer, how much power it steals?

[katinas]

Wob, your advise about restored C open duration, really helped at the race. Boy finished in the second place at the European Championship Mx65 final.
Many thanks.

[Flettner]

When talking balanceshafts, i now run a verion in my engine like the aprilia type.
One weight on each side of crank as close as possible to the center och the crankshaft.

Is there any data recorded with or without balancer, how much power it steals?

In my particular case, parallel twin cylinder, the difference of with or without a balance shaft is the difference between flying or not. Without, the vibration was so bad I was sure sooner or later the engine would crack the engine mounts and rip itself out.
Balance shaft in all my furure designs for sure.

[SwePatrick]

In my particular case, parallel twin cylinder, the difference of with or without a balance shaft is the difference between flying or not. Without, the vibration was so bad I was sure sooner or later the engine would crack the engine mounts and rip itself out.
Balance shaft in all my furure designs for sure.

Yes, i feel the same.
But when dynoing my engine before the race a couple of weeks ago(after adding the balancer) i had lost a lot of power, it might be something else i messed up(many other mods), but as it seized in the bigend i can´t get the answers just yet.
From 69hp to the rear wheel to 57hp(when it seized, but it was heading above 60hp)
I figure i might have lost 2-3hp on the balancer, but it would be interesting with actual numbers from someone that has seen the diffrence.

[wobbly]

Frits yes you are correct ( theoretically as always ) but in practice a single balance shaft with eccentric weights on each end
or a single long offset cut shaft has such a profound effect on vibration as too negate any issues such as rocking torques,
Perfect example is when I tried to run TZ400 at 90*.
This prety much eliminated the couple across the crank but created a resultant force ,partially from each pistons position relative to
each other , that buzzed the bars and seat so bad it hurt.
KTMs 250GP parallel twin engine ran at 90* with a shaft and as I knew the designer he allowed me to warm one up in the pit lane at Philip Island.
No discenible vibration at all.

Katinas - once I have racing out of the way , the first thing I will be doing is to get a piston radius cut and lift the C the same amount
as the cylinder is dropped.
I have already fully optimised the timings , so this will be a good pointer for anyone trying this idea.
Then I will do the boost port duct step - and put the dyno sheets on here a s well.
Thanks for that idea.

[jamathi]

When talking balanceshafts, i now run a verion in my engine like the aprilia type.
One weight on each side of crank as close as possible to the center och the crankshaft.

Is there any data recorded with or without balancer, how much power it steals?

I tried this at Garelli.
Without balancer the engine gave 1,7HP LESS!
I just removed the drive gear, without 'opening' the engine.....