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rotating assembly balance |
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401jim
Supporter of TheAMCForum Joined: Jan/07/2012 Location: Brunswick,Ohio Status: Offline Points: 793 |
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Whatever the cost...... Just do it! As ross says and I agree, Balance any engine....
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19676 |
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I've rebuilt MANY stock engines and never had a one balanced. Never a problem, but I do know for sure that I had all the correct stock parts as well. If you change the flywheel or flexplate on an AMC V-8, there is a bigger chance you will have to balance. Smaller chance if you change the "balancer" (actually vibration dampener) on the front, but there are at least two different ones. Balance is mainly affected by the weight and position of that weight on the flywheel/flexplate. That's why it's important to have the correct one for your engine. Doesn't have to be the original, but the right one for the displacement (and in a few cases the year -- like the 70 390...).
If you want an engine to live over 5000 rpm you need to balance though. A stock AMC V-8 will tolerate an occasional short burst over 5K with no issues. But if you plan on running it like that often, balance! Normal warmed over daily driver/cruiser, don't worry much about it -- stock balance should be fine UNLESS something is mismatched. Your machine shop might just be doing a "poor man's balance". What they do is make sure all the pistons weigh within a few grams (tenths of an ounce) and each end of the connecting rods are the same. This helps a lot, but isn't a full balance job -- crank and flywheel weights aren't altered. If you have a digital scale that measures in at least tenths of an ounce (0.0... 0.00 would be better) you can do this yourself. A digital postal scale should be fine -- that's what I use. Simply weigh all pistons, then pick the lightest. Make the others match the lightest as close as you can by taking a little off inside above the wrist pin. For the rods make a stand for one end. A couple pieces of 2x4 with a nail is all you need. Support one end with the stand, rest the other on the scale. Weigh one end of all rods, pick lightest, then grind a bit off the pad on the cap (big end) or top (small end) until all are about the same. I always record the weight of each stock, then the new weight as I go. You should be able to get them all with 0.1 ounce or less. This will greatly reduce stress on the crank without the expense of crank balancing. It's half a true balance job, but cheap and easy. On a straight six this is all the balancing you need to do, as the crank is "naturally balanced" -- weights are equally spaced around the crank. The only other "naturally balanced" configuration I can think of is a horizontally opposed engine -- any cylinder count. Easy to see why -- one piton is directly opposite another. |
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Frank Swygert
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90islander
AMC Apprentice Joined: Aug/27/2017 Location: flora il Status: Offline Points: 31 |
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Sorry I forgot to post that it's going in a Jeep that is trail road and road driving some also it very rarely sees 3500-4000 rpm with the 304 that is in it now
Thanks josiah |
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