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Old 09-13-2020, 11:16 PM   #1
31jalopy
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Default counter weights are they needed?

Ok if building a good street/performance motor and have a respectively light flywheel do you need counter weights? most people add weights to smooth out vibrations caused by weight of stock flywheel on crank/flex and main bearing stress, but if weight is greatly reduced from flywheel you gain smoother rotation forces? plus with no weights on crank less stress and force?energy/Horse Power from pistons.



Yes everything balanced individually then as one mass. pressure plat,flywheel,crank,pulley so if balanced properly do we need counter weights?



cheers guys

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Old 09-13-2020, 11:37 PM   #2
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Default Re: counter weights needed?

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Originally Posted by 31jalopy View Post
Ok if building a good street/performance motor and have a respectively light flywheel do you need counter weights? most people add weights to smooth out vibrations caused by weight of stock flywheel on crank/flex and main bearing stress, but if weight is greatly reduced from flywheel you gain smoother rotation forces? plus with no weights on crank less stress and force?energy/Horse Power from pistons.

Yes everything balanced individually then as one mass. pressure plat,flywheel,crank,pulley so if balanced properly do we need counter weights?

cheers guys
Yes.
Crankshaft counterweights are added to offset the weight of the rods and pistons, not the flywheel.
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Old 09-14-2020, 12:36 AM   #3
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Default Re: counter weights needed?

but not all engines are counter weighted and yes i know its to counter weight rods and pistons but what experience have you guys found/had? smoother, revs higher?
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Old 09-14-2020, 07:19 AM   #4
BRENT in 10-uh-C
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Default Re: counter weights needed?

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but not all engines are counter weighted and yes i know its to counter weight rods and pistons but what experience have you guys found/had? smoother, revs higher?
When I read this topic, the keyword is "needed". Are they "needed"? 'No' is my answer. Are they an advantage? 'Yes'. Is it smoother? 'Can be.' but not always. Does it "rev higher"? Counterweights typically have no affect on how many RPM the engine can rev. The carburetion and induction system generally controls that.
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Old 09-14-2020, 08:51 AM   #5
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Default Re: counter weights are they needed?

I was going to post this link,

https://www.jalopyjournal.com/forum/...heels.1202985/

and then saw you started it...

In my experience they typically run smoother. But then it's a while since I drove a stocker. Either way, as I've said, anything that keeps down the vibrations will help keep the bits inside longer.
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Old 09-14-2020, 09:05 AM   #6
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Default Re: counter weights are they needed?

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i dont think there is a modern engine without counter wieghts. you are not correct in your thinking that a lightened flywheel will be better, easy on things.
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Old 09-14-2020, 09:14 AM   #7
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Default Re: counter weights are they needed?

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i dont think there is a modern engine without counter wieghts. you are not correct in your thinking that a lightened flywheel will be better, easy on things.
I like the heavy flywheel. Makes the car almost impossible to stall on takeoff. One of the reasons i plan to teach my grandkids to drive on my Model A, That and how many kids today can say they learned to drive on a Model A?.
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Old 09-14-2020, 11:55 AM   #8
BRENT in 10-uh-C
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Default Re: counter weights are they needed?

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i dont think there is a modern engine without counter wieghts. you are not correct in your thinking that a lightened flywheel will be better, easy on things.
Using your same logic, "I don't there is a modern..."

-vehicle with mechanical brakes.
-vehicle that doesn't have air bags.
-vehicle with a manual transmission that doesn't have synchronizers.
-production vehicle manufactured with a carburetor.
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Old 09-14-2020, 12:12 PM   #9
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Default Re: counter weights are they needed?

Counterweights reduce torsional vibration,a cause of main bearing failure.Ask yourself what you aim is for the car? Highway speed touring? Then yes counterweights..hill climb short burst 'barhopper' banger? Dynamic balance is good,the lighter crankshaft spools up quicker.

During A engine design Mr Ford felt the heavy flywheel dampened impulse,his engineers 'argued' for a heavier crankshaft,the 'new and improved model b came with a heavier,then counterbalanced crankshaft.

Mechanical brakes and spur gears make it a model a..
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Old 09-15-2020, 12:40 PM   #10
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Default Re: counter weights are they needed?

The heavier flywheel allows for lower rpm in operation. Low rpm engines have less problems with higher harmonics. Counterweights allow for a wider rpm band and reduce the need for a heavy flywheel. Ford had counterweights on the model B for 1932 but they still had a vibration damper on the firewall to reduce the chance of vibration resonance.

Opposed aircraft piston engines have all sorts of counterweight configurations depending on the rpm and power application that is is designed for. Some have a large heavy prop and some have a lighter prop. Then there are helicopter engines that have almost no flywheel at all. It's basically only a cooling fan with a starter ring on it. The rotor system is the flywheel on most of them and they are easy to over speed during start up. If they over speed with too high an rpm, it can stretch the connecting rod and lead to crank pin or con rod failure.
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Old 09-15-2020, 07:28 PM   #11
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Default Re: counter weights are they needed?

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Ford had counterweights on the model B for 1932 but they still had a vibration damper on the firewall to reduce the chance of vibration resonance.

Not all B engines had counterweights, i have 3 diamond block engines and only one had counterweights.
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Old 09-15-2020, 07:44 PM   #12
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Default Re: counter weights are they needed?

Counterweighted crankshafts started in late 32..
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