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Discussion Starter · #1 ·
So I'm not new to mustangs or cars in general but this is my first motor build. I plan on putting around 500 horses to the ground. I was looking into balancing my bottom end because I got killer deals on a rotating assembly. I am definitely going to get everything checked for straightness and stress cracks because they are used, and I am definitely getting my rods and pistons balanced even though they are already assembled and probably OK. My question is, how important is it to get my crank balanced to my dampener and flywheel? I've heard my motor is internally balanced. The reason I ask is because my machine shop sends parts out to another company to get it balanced and they want about $400 just to do the crank. Its an 03 cobra block and a 98 cobra crank if it matters.
 

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The engine is internally balanced. It doesn't need to be balanced with the balancer and flywheel.
 

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And balanced.
 

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If its internal balanced, the pulleys, balancer and flywheel should be balanced to zero, however, every motor I've had balanced, they always wanted everything from the crank pulley to the pressure plate. Guess it depends on how exact you want it. Usually the ones externally balanced, like a 428 FE, I had internally balanced anyway using heavy metal.
 

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when you start changing internal weights, you need to balance. internal/external is just description where balance weight is at, not if it ever needs balancing or not. i always balance from balancer to pressureplate/flexplate. we add the dampner, fly, and pp just to get them exact. they dont have to be messed with, but its an extra step i like to take.
 

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Discussion Starter · #8 ·
OK, above it was stated that the crank needs to be checked and balanced but not to the external parts. What would it be balanced to? If it needs to be done then I will do it from dampener to pp but if there's really no reason then I will just save $400.
 

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You bring the machine shop your rotating assembly (crank, rods, and pistons). They will weigh everything and install counterweights on the crank to dynamically balance the crank to the rods and pistons.
 

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Discussion Starter · #10 ·
OK, sorry for asking so many questions but I am kinda a noob when it comes to this stuff. My machine shop says balancing the crank and balancing the rods and pistons is to completely separate jobs. He said they weigh all the piston and make sure they are all the same weight, same with rods. Then separately they will balance the crank to external components. So I'm getting conflicting responces lol. Should I find a new machine shop?

---------- Post added at 02:50 PM ---------- Previous post was at 02:27 PM ----------

OK well I called another machine shop and they are exactly in line with what you guys are saying. I was getting confused from what the first shop told me. The second shop is a lot cheaper as well. Guess I found my shop lol.
 

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They weigh the pistons and match them all to the lightest one via grinding. They weigh the big and small ends of the rods separately and match them as well. They then take the weight of the rod's big end and add a percentage of the small end + piston weight (since these are reciprocating and not 100% rotating) and attach bob-weights to the crank that represent this total calculated weight. Then spin and balance. They can grind material off the crank counter weights or drill a hole in the counterweight and weld a heavy Mallory metal plug in it to add weight if alot is required. Including the balancer, flywheel and PP will just allow them to get the balance more precise, but then everything kinda becomes a matched assembly. In theory, these components are already zero balanced, but nothing is perfect.
 
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