crankshaft balancing

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divebuzzards
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Joined: Mon Jul 09, 2018 1:43 pm

crankshaft balancing

Postby divebuzzards » Tue Jul 10, 2018 11:20 am

Has anyone had any luck balancing a crankshaft on a 60's big twin? It seems that these engines weren't built with a decently balanced rotating assembly. I'm curious to see if anyone has had any experience with this? I have several crankshafts and they all seem to settle differently while laying horizontally on a balancing rail.

FrankR
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Re: crankshaft balancing

Postby FrankR » Tue Jul 10, 2018 1:07 pm

Yeah, I tried it. Removed shocking amount of metal. Motor vibrated as much or more than it did before. Conclusion: There is more to it than meets the eye.

divebuzzards
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Re: crankshaft balancing

Postby divebuzzards » Tue Jul 10, 2018 1:11 pm

What amazes me is that the same crankshaft is used with the two ring 70's 40hp engines and that piston and rod assembly is over two ounces heavier than the three ring assemblies of the earlier models. I guess they just weren't worried about vibration.

XR55
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Re: crankshaft balancing

Postby XR55 » Tue Jul 10, 2018 2:05 pm

Maybe the rotating assembly crank rods and pistons were balanced with the flywheel as one unit somehow.

FrankR
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Re: crankshaft balancing

Postby FrankR » Tue Jul 10, 2018 3:13 pm

That's what I figure. The flywheel is part of the equation.

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Richard A. White
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Re: crankshaft balancing

Postby Richard A. White » Tue Jul 10, 2018 3:38 pm

Or the flywheel was actually the part that was modified to balance the entire assembly????

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Tubs
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Re: crankshaft balancing

Postby Tubs » Tue Jul 10, 2018 4:13 pm

The pulse from ignition also needs to be considered.
It has a considerable effect on single horizontal firing
Motors. The more even the pulses around the rotation
of the crankshaft the less effect in has on vibration.
V-12's & V-16 being the smoothest even in the 1920's & 30's
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JoeCB
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Re: crankshaft balancing

Postby JoeCB » Tue Jul 10, 2018 4:25 pm

A lot more complicated that meets the eye!! talking to an automotive engine designer ( we have several up here around Detroit) and you just begin to understand the complexity of engine "balance".

Joe

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Tubs
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Re: crankshaft balancing

Postby Tubs » Tue Jul 10, 2018 7:05 pm

AND= when the ignition pulse is part of the equation
they can only be balanced a a certain RPM. It can
be at any point but when you go above or below
that point they go back out of balance some. Its
why the motors in these things are rubber mounted.

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zul8tr
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Location: Orlando

Re: crankshaft balancing

Postby zul8tr » Wed Jul 11, 2018 5:11 am

Well since you asked here are engine balance basics, never said it was simple:

https://motochassis.com/Articles/Engine ... alance.pdf

How about this method, gotta watch the fingers?

https://www.bing.com/videos/search?q=ou ... ORM=VRDGAR
Keep Movin' - Life is catching up :o


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