balancing crank

[lorca]

Hi every one, i have a qustion to ask how balancing is done ? as i took my dpr 69mm crank with the lightweight fly wheel, pressure plate, and equaliser 5.7lbs pulley to the machine shop for balancing.

Its seams that he didn't assembled the pully while balancing as it wasn't attached to the crank, does it effect? I couldn't ask him as i didnt went to pick up the crank and i need to wait till monday,

As i was doing some research on youtube and cb performance do the balancing as it was done to mine. [/youtube] https://youtu.be/sD4GEAI7sXA

But on john maher site they even install the pully and timing gears to the crank.
http://johnmaherracing.com/machine-work/balancing/

I know that balancing with timing gears and pully is better than without them. But balancing without timing gears and pully will effect the crank when installed ?

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[Quokka42]

Balancing is done g-cm, so the timing gears and pulley matter sweet FA unless you are turning very high revs and/or have a heavier "equaliser" style pulley.
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[vwracerdave]

Those video's only show part of the balancing process.

First you balance the crank all by itself. Then you add the flywheel and balance again. Then you add the pulley and balance again. Many people argue but the pressure plate should be balanced independently by itself so it can be replaced when damaged without effecting the other parts. If the pressure plate is balanced on the crank & flywheel then you must rebalance the entire assembly when you replace the pressure plate. The front pulley can also be balanced independently like the pressure plate.

Yes the gears should be installed on the crank. It probably makes very, very, very little difference on a street engine at 3200 RPM highway cruising speeds but the timing gears could make a difference at 7000 RPM racing speeds. It all makes a difference.
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[fivelugshortaxle]

[Boolean]

Of course gears and pulleys must be balanced.
A factory "balanced" pulley can easily be 5-10 grams out.
You don't actually correct gears, but they have to be there for the spin because they are not symmetrical.
Another tidbit: Balancing have no linear relation to rpm. Or rather, it does, but that's not the whole picture. Every crank system has resonant or critical points in it's range. You don't want to excite those more than necessary.
Completely stock engines have these under control, but as soon as you modify the engine all bets are off.
I have always advocated to do balancing to the very best precision the instruments can handle. It does not take much more time than doing it badly.
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[Juanito84]

Would any, let's say, balance shop in Denver be ok? How do you know who to trust to do a good balance job?
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[esde]

[g3bill]

If you purchased a CW stroke crank for street use (below 6000rpm) from a good shop like dpr, is there really any reason to have it balanced again as there balanced during production they say. Or must one ask to balance to within 1gm. & pay extra? Same thought with flywheel...
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[nsracing]

The crank and gears + keys are balanced first.

The pulley and flywheel can go on the crank at the same time. They are on opposite sides LEFT and RIGHT so you read that on the machine. You can do them both at the same time. They don't have to be done separately.

AFter you get the unbalances where you need them, then hang the pressure plate.

I just balanced an assembly and the EMPI pressure plate was out by 4 ounce inches. 1 ounce = 28.34 grams. It took some MIG welding the light side and taking some from the heavy side to get that down to 0.4 ounce

I have to add though that I have never seen a German or Brazilian pressure plate that much out of balance.

[Quokka42]

Have you ever seen a pulley or gear out by that much?
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There has only ever been one man who was perfect, and they nailed Him to a cross.

[Bruce]

[mark tucker]

my old berg heavy junk pully was out more than I figure it should of been.(not the super heavy extra junk parts maker equlizer) every aluminum pully Ive ever done or had done have been very close.I personaly would /could swap aluminum pullys with no worrys. I tried to get DRD to balance my 86 crank with the gears&keys...not...also flywheel attached....not. I wish CB had that crank at that time oh well live &learn. balancing is fast&simple on these cranks....but you cant fix stupid.

[nsracing]

Aluminum pulleys will normally spin very low on the balancer. Single can be mounted on a precision mandrel and spun by itself.

Or.. you can have it spin on its crank.

It is the pressure plate that really screws up your work. AS you hang the pressure plate, that unbalance will affect both sides. So just keep that in mind. You do the correction only on that side where you hang the new item. The other side will eventually come down as the unbalance gets smaller.

Balancing the clutch disk might be a good idea, but it is not standard practice.

Come to think of it, maybe I will mount one on a mandrel and see how far out it is.

[mark tucker]

chunks missing out of disc can be a headache. Ive often wondered how close a disc was.