Internally balanced 360 crank
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From: Arkansas
Internally balanced 360 crank
I had the crankshaft on my 360 Magnum internally balanced with tungsten by my engine builder. I'm very close to putting the engine back in the truck and I need to know what I need to do to support this mod.
318s are internally balanced while 360s are externally balanced. Is this external balance just a weighted flexplate? In other words, now that my crankshaft is internally balanced, do I just need to replace the weighted 360 flexplate with the unweighted flexplate from the 318 or do I need to replace other stuff as well?
318s are internally balanced while 360s are externally balanced. Is this external balance just a weighted flexplate? In other words, now that my crankshaft is internally balanced, do I just need to replace the weighted 360 flexplate with the unweighted flexplate from the 318 or do I need to replace other stuff as well?
Champion
Joined: Sep 2012
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From: Central VA
Yes, you need a flexplate from a 318 (unbalanced) and also a harmonic balancer for a neutrally balanced motor. You may be able to use a 318 balancer, but will have to check for fit on the crank. I'd discuss this with your machinist that did the crank balancing. If you've gone through the trouble of balancing the crank, I'd consider going with a nice SFI approved balancer, too.
Captain
Joined: Sep 2013
Posts: 586
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From: Nevada
You will need the 318 balancer and the flex plate as HeyYou said. The 318 balancer is a direct swap thankfully.
One thing to watch for, look at your current flex plate AND converter to see which has the weights. Different trucks have the weights in different spots... Even in the same year.
One thing to watch for, look at your current flex plate AND converter to see which has the weights. Different trucks have the weights in different spots... Even in the same year.
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From: Arkansas
The harmonic balancer is definitely a different part number between the 318 and the 360, but the 360 harmonic balancer says it is neutrally balanced in the description, so I was thinking I could leave it be??
Why internally balance? When a rotating assembly is balanced along its axis of rotation but outside of the center of its rotating mass, the axial inertia is balanced but there will be oscillatory motion about the center of rotational mass (think standing waves in a vibrating guitar string). This small amount of oscillation does not exist in a perfectly internally balanced rotating assembly. Crankshaft oscillation results in stiction at the crankshaft journals and thus increased rotational drag. More importantly to me, crankshaft oscillation means increased variability and unpredictability in piston to head clearance with increased RPM, so that if all pistons measured the same head clearance at assembly, when at 5000 RPM, some pistons may be a couple thousandths higher at TDC than others. As I was already rebuilding the whole thing, and I wanted a somewhat scary quench of only .030", I saw this as a way to reduce that variability a little.
This is probably a good time to say "you're overthinking this"
Why internally balance? When a rotating assembly is balanced along its axis of rotation but outside of the center of its rotating mass, the axial inertia is balanced but there will be oscillatory motion about the center of rotational mass (think standing waves in a vibrating guitar string). This small amount of oscillation does not exist in a perfectly internally balanced rotating assembly. Crankshaft oscillation results in stiction at the crankshaft journals and thus increased rotational drag. More importantly to me, crankshaft oscillation means increased variability and unpredictability in piston to head clearance with increased RPM, so that if all pistons measured the same head clearance at assembly, when at 5000 RPM, some pistons may be a couple thousandths higher at TDC than others. As I was already rebuilding the whole thing, and I wanted a somewhat scary quench of only .030", I saw this as a way to reduce that variability a little.
This is probably a good time to say "you're overthinking this"
Last edited by Big Green 360; Jan 3, 2017 at 11:40 PM.
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From: Clayton MI
The harmonic balancer is definitely a different part number between the 318 and the 360, but the 360 harmonic balancer says it is neutrally balanced in the description, so I was thinking I could leave it be??
Why internally balance? When a rotating assembly is balanced along its axis of rotation but outside of the center of its rotating mass, the axial inertia is balanced but there will be oscillatory motion about the center of rotational mass (think standing waves in a vibrating guitar string). This small amount of oscillation does not exist in a perfectly internally balanced rotating assembly. Crankshaft oscillation results in stiction at the crankshaft journals and thus increased rotational drag. More importantly to me, crankshaft oscillation means increased variability and unpredictability in piston to head clearance with increased RPM, so that if all pistons measured the same head clearance at assembly, when at 5000 RPM, some pistons may be a couple thousandths higher at TDC than others. As I was already rebuilding the whole thing, and I wanted a somewhat scary quench of only .030", I saw this as a way to reduce that variability a little.
This is probably a good time to say "you're overthinking this"
Why internally balance? When a rotating assembly is balanced along its axis of rotation but outside of the center of its rotating mass, the axial inertia is balanced but there will be oscillatory motion about the center of rotational mass (think standing waves in a vibrating guitar string). This small amount of oscillation does not exist in a perfectly internally balanced rotating assembly. Crankshaft oscillation results in stiction at the crankshaft journals and thus increased rotational drag. More importantly to me, crankshaft oscillation means increased variability and unpredictability in piston to head clearance with increased RPM, so that if all pistons measured the same head clearance at assembly, when at 5000 RPM, some pistons may be a couple thousandths higher at TDC than others. As I was already rebuilding the whole thing, and I wanted a somewhat scary quench of only .030", I saw this as a way to reduce that variability a little.
This is probably a good time to say "you're overthinking this"
Your reasoning is sound though. Not sure if it is absolutely necessary, but, a nicely balanced motor will rev smoother, and last longer... so, certainly not a complete waste.
According to theory....... For the 96 model year, the balance weights moved from the torque converter, to the flexplate, although, there are likely exceptions to that rule. Including one member with a 96 truck with an RH trans....... (and it's the only one I have ever seen......)
