To clear up confusion, are you referring to the idler shaft, which drives the fuel pump (carb), distributor (8V) and oil pump? This shaft rotates at half crank speed and does not provide harmonic balance, it does however increase the smoothness due to increase of rotating mass. A true harmonic balancer shaft on a 4 cylinder inline engine would need to rotate at twice crank speed, to damp 2nd order harmonics. To properly damp all the harmonics, there would need to be 2 shafts.
I'm refering to the function of harmonic balancer, in general, which the idler shaft isnt, as you say. The crank bob-weights don't rotate at twice crank speed...
Ok I sort of see where you're coming from: If a car has a harmonic balancer, you can fit lightened pistons and remove the harmonic balancer. This makes sense, since it is designed to smooth out 2nd order harmonics due to (up and down) piston movement. The crank bob-weights smooth out 1st order rotational forces.
As i understand: A harmonic balancer is needed where the rotational forces of the crank counterwieghts are not enough to cancel out the reciprocal forces of the pistons. Bigger counterwieghts is the internal balancing solution, harmonic balancers are the external solution.
you are kidding me.....my engine spins beautifully all the way to 8.5K and has no balancer in the front pulley, just a lump of ali, super smooth, way more so than a std production engine and it idles just fine - and this is with a very light flywheel and 7.25" ali race clutch
it does actually - a well balanced engine will have less friction at the bearings resulting in more power at the flywheel
If you've reduced crank counterweights AND fitted lighter pistons, then this is lightening without 'unbalancing'. There's 2 types of smoothness, there is the evenness of the torque delivery (inertia) and the balance of the crank in rotation. Another aspect of blueprinting which has not been mentioned yet is matching pistons to the same weight. Since the design of the 4-cyl inline uses pistons in opposition to each other to give 1st order up-down balance, this gives good balance. If you have lightened the components (including pistons) and balanced components too, it could be smoother than stock.
I think he meant it doesn't directly influence power. It (indirectly) reduces losses through friction so it will increase overall efficiency and therefore power.
Well, i've had a read and i'm too thick to understand this bit: ...In contrast, in a straight-four engine, rotate the crankshaft a certain angle, the piston near the top end has a displacement (b), larger than that of another piston near the bottom (a). As vertical force is the product of displacement and mass of piston and divided by the time taken for such displacement, you can see the different displacements must lead to different forces, therefore complete cancellation is impossible. The resultant force is the aforementioned second order force, which rotates at twice the speed of the crankshaft.
The piston at the top goes down quicker than the piston at the bottom goes up, so they don't cancel out. It goes down quicker because the rod is at a bigger angle off the vertical (Pythagoras theory).
I found another link, which might help because it explains it in a different way: http://www.answers.com/topic/balance-shaft
i have had my fly wheel and clutch asembly lightened as far as you can go. also got old of a early audi td crank pully ,its about half the size of a standard 2 litre pully, got hotgolf to lighten it, and make a shim to alighn it , works a treat , revs up real quik and crispy, alters your fan belt size though.
how can that happen if they are attached to the same part? surely any speed gained going down forces the crank around pushing the opposite piston to the same speed?
Because of the angular movement of the con rod The piston moving down moves down because the conrod moves sideways (thats one count of pulling it down) and the crank pin moves down (Thats two counts of pulling it down) The piston moving up is pushed up by the crankpin moving up ( thats one element of moving up and to the same degree as the piston moving down) while the con rod moves sideways so effectively PULLING THE PISTON DOWN and effectively partially cancelling crank pin element of moving up. A strange concept I know until you have figured it out. Yes they are both attached to the same part but not directly - this is the crucuial part - they are attached by rods at angles. The angular movement affects the relative accelerations.
Talking purely in terms of distance travelled, or diplacement. It's difficult for (a) and (b) in the diagram to be different. Especially with the implied shared centre line for crank and pistons.
I didn't believe it myself either - but drew it out last night (geometry set and all LOL) and its right, when at the bottom of the stroke the rod is more angular to the vertical than when at the top of the stroke resulting in different piston distances travelled for a given angle of crank rotation - its easy to understand if you draw it out
