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Old 03-15-2010, 11:16 PM   #1
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Default Crankshaft Balancing

I would like to know if there are any modders that does crankshaft balancing?
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Old 03-15-2010, 11:36 PM   #2
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I would like to know if there are any modders that does crankshaft balancing?
Balancing is determend what type of driving you do and what kind of car your engine is in. Crank timing balance is when you want the inertia to start building. Guys who drag race don't want inertia for the 132 ft. You would want velocity. Now the guys who do on road or street drags need to build inertia to carry them through. Setting the crank timing balance is where the weight is placed so it takes more time to roll over at TDC and BDC "0 Dergee or at 180 degree" or less time to roll over. Tork you would want more weight aft so it hold the piston at the top a split second longer giving a longer burn cycle, more power. Weight forward on crank will let it roll over faster giving you more speed but less power.
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Old 03-16-2010, 12:18 AM   #3
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WAIT A MIN.....crank balance and crank timing are 2 completely different things. Crank balancing is weight of the piston and rod assmbly put on the as bob weight and spin the crank take or add weight as needed to balance the crank. Crank balance if off alittle will cause a vibration can lead to failure fast. OH timing has to do with where the opening is cut in the crank.
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Old 03-16-2010, 08:00 AM   #4
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WAIT A MIN.....crank balance and crank timing are 2 completely different things. Crank balancing is weight of the piston and rod assmbly put on the as bob weight and spin the crank take or add weight as needed to balance the crank. Crank balance if off alittle will cause a vibration can lead to failure fast. OH timing has to do with where the opening is cut in the crank.
There is no way to balance a crank with one piston running up and down. All you have is crank timing balance. If you look at onroad engines you will notice the lugs in the cranks. That is what gives them the torque. In off road cranks like the Nova Rossi there is no lugs. Crank induction timing is something intirely different.
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Old 03-16-2010, 08:44 AM   #5
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There is no way to balance a crank with one piston running up and down. All you have is crank timing balance. If you look at onroad engines you will notice the lugs in the cranks. That is what gives them the torque. In off road cranks like the Nova Rossi there is no lugs. Crank induction timing is something intirely different.
Sorry man but that is totally false, slugs are for balancing the rotational movement of the crankshaft, timing has nothing to do with balancing. I know calling it balance on a single stroke is a stretch, but still, balance it is since there's maybe no other word for it. Mr Mustang is right.

Neither does weight, weight and balance and timing are three, totally independent things.

I balance all the cranks a touch, there is a lot of performance hidden in there.

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Old 03-16-2010, 08:45 AM   #6
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Sorry man but that is totally false, slugs are for balancing the rotational movement of the crankshaft, timing has nothing to do with balancing. I know calling it balance on a single stroke is a stretch, but still, balance it is since there's maybe no other word for it. Mr Mustang is right.

Neither does weight, weight and balance and timing are three, totally independent things.

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I am siding with Rick on this one..the slugs are to add ballast to the rotating assembly...
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Old 03-16-2010, 08:54 AM   #7
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Both sides of this discussion are correct.

However Maximo and Rick are touching on balancing the crank (though actually out of balance) to create inertia to help build torque or to actually help the piston into and through its dwell (before and during).

This "extra" weight can be installed in different "timings" to create where it will increase power.
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Old 03-16-2010, 08:58 AM   #8
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Nope, weight adds momentum, inertia, has nothing to do with torque. Remember that torque is the amount of twisting force that the crankshaft is applying to the drivetrain, the weight adds to the inertia, and it is part of the forces that are acting AGAINST torque while it is applied.

once you accelerated the weight, it is called momentum and then it will be hard to stop it only then, after you spent all the energy (gas) trying to speed it up.

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Old 03-16-2010, 09:04 AM   #9
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Just weight ! more mass to resist rapid acceleration or deceleration..... smoother power delivery with less spikes between the powerstoke....Also helps resist rapid RPM increase in low load situations....
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Old 03-16-2010, 09:11 AM   #10
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So, maxflo, why is the balance weights placed on different positions on the crankshaft? If they only are there to make a larger inertia, you could just have let the crank look like an RB WS7. Thing is, taht it is not the same were you place the weight.

If you look at a Nova and compare to an RB, the weights is not placeds at the same place..
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Old 03-16-2010, 09:24 AM   #11
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Just weight ! more mass to resist rapid acceleration or deceleration..... smoother power delivery with less spikes between the powerstoke....Also helps resist rapid RPM increase in low load situations....
Those are all good points my friend, and largely used by all manufacturers.

AM,
That's not what I said, I said that overall/total weight only adds inertia/momentum, slugs are placed where they do their best work, obviously if we're talking about a good designer/manufacturer, remember not all cranks are created equal. Not just the shape of the pendulum, or the location of the slug, or quantity of slugs is responsible for that balance, there's much more to it than that.

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Old 03-16-2010, 09:35 AM   #12
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Default Crank Mass Is Relative To Torque

If you dont believe me look at a top fuel drag crank and a F1 crank. Hook that Ferrari up to those big ass tires redline the motor drop the clutch and watch it grenade!! Yes enertia is part of the equation -a object in motion tends to stay in motion. I think the original post was in refrence to harmonic balancing. Which is different than what Rick was talking about balance of the crank lobe mass for manupulation of the engine power curve. If crank mass wasnt relative to torque I would all be driving 4 cylinders with ultra light cranks 20k rev limit instead of my F250 with a 3k redline.
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Old 03-16-2010, 09:42 AM   #13
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You guys should try driving a car with a lightweight flywheel in the Canadian winter.... A few years back i put a 9lb flywheel into a car that normally runs a 28 lb flywheel....due to unseen circumstances i ended up having to drive that car for most of a winter.... Wow talk about useless !
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Old 03-16-2010, 09:45 AM   #14
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Default I With Rick On This

[QUOTE=maxflo777;7144180]Sorry man but that is totally false, slugs are for balancing the rotational movement of the crankshaft, timing has nothing to do with balancing. I know calling it balance on a single stroke is a stretch, but still, balance it is since there's maybe no other word for it. Mr Mustang is right.

Neither does weight, weight and balance and timing are three, totally independent things.

I balance all the cranks a touch, there is a lot of performance hidden in there.

If they were just trying to balance against a fraction of the piston/rod(not the entire wieght is offset because of pivot/balance points of the stroke) Why not just drill out to remove wieght. The lugs are usually made of tungsten-very heavy. They are there to ADD mass in specific parts of the lobe. Adding mass to a steel crank to offset a aluminium piston is not neccessary to harmonicly balance a crank.
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Old 03-16-2010, 09:52 AM   #15
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If you dont believe me look at a top fuel drag crank and a F1 crank. Hook that Ferrari up to those big ass tires redline the motor drop the clutch and watch it grenade!! Yes enertia is part of the equation -a object in motion tends to stay in motion. I think the original post was in refrence to harmonic balancing. Which is different than what Rick was talking about balance of the crank lobe mass for manupulation of the engine power curve. If crank mass wasnt relative to torque I would all be driving 4 cylinders with ultra light cranks 20k rev limit instead of my F250 with a 3k redline.
Again, no. You are mixing things
Don't look at the cranks only look at the flywheels also... flywheels are 4inch diameter and almost all made of carbon fiber and aluminum... to get rid of weight.

Cranks have all those weights for a very different reason - balance, remember those are 4 6 8 10 12 cylinder engines what ever, not the same as a single or 3, 5, 7 cylinder engines that wont ever balance to the fullest.

Inertia, or crank mass is used to help keep an engine at a given rpm. lets say you are pulling some thing with your truck, and its heavy, 1st gear 2,000rpm second gear - the super heavy flywheel/crank assy has a lot of inertia and helps the motor at trying to stay at 2,000rpm and converting that to acceleration, again, nothing to do with torque.

same for the little 4 cylinder.

Actually, if you want to feel real torque get rid of the steel flywheel and put an aluminum one, you'll feel the torque pushing on your back when you push he throttle and the engine doesn't have to move that chunk of steel from 1,000 rpm to 7,000rpm in a second.

And I am not saying that the slugs are bad, I only have slugged cranks in my engines, I'm explaining their function by balancing, not just adding weight where ever.

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