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Big block- Balancing rotating assembly...

Discussion in 'The Garage' started by Zeus33rd, Jul 4, 2003.

  1. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    I've been in the middle of gathering parts to rebuild my big block the last couple months. Just picked up a new crank the other day, and someone mentioned that I should get it balanced. I called the machine shop and they want $175 to do it. Plus $65 to remove the pistons from the rods and reinstall when finished. The guy said there's also a possibility the pistons could get damaged from being removed. Is it worth the money to have done? I would ask for pro's and con's, but I'm not sure of there are any con's really....Basically asking why is it a good idea and is it worth the time? /forums/images/graemlins/1zhelp.gif
     
  2. tarussell

    tarussell 1/2 ton status

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    In my opinion it is money WELL spent !!! If the funds exist than always get the rotatating assy. balanced and always do it if the motor will see any lengthy RPM - even if it is relatively stock.
    Your balance shop will need the entire rotating assy. including :
    crank
    rods
    pistons
    one set of rod bearings & rings for one piston
    harmonic balancer
    flywheel/flexplate
    Remember if you were to change the balancer or flywheel with another after the balance job than the final balance will be affected.
    Quality machine work , including balance , will go a long way towards a healthy and durrable engine life.
    Good luck , Tom
     
  3. thatK30guy

    thatK30guy 1 ton status Premium Member

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    I agree with tarussell. Balancing will prolong the life of the motor.

    I have seen several different shops do different methods. Some shops want the crank, balancer, flexplate/flywheel, and just one piston/rod. Avoid these shops as you want to use a reputable shop that will use all 8 pistons/rods to balance the whole rotating assembly.

    I watched two different rebuilt engines run in which one was balanced and the other was not. Both were built along the same lines as the other. The difference was the non-balanced engine "rocked" more in the engine bay than the balanced engine did. The balanced engine was idling and running so smoothly, even when you rapped the throttle, it would still run very smoothly in the bay.

    Balancing an engine is money well spent. Such job will allow your main and rod bearings live longer. /forums/images/graemlins/wink.gif
     
  4. fortcollinsram

    fortcollinsram 1/2 ton status

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    Get it done...You'd be surprised how out of balance even factory engine are...Ia balance job was mandatory in my situation b/c I put kept the stock crank and put in new H-beam rods and Hyper pistons...My rods and pistons are MUCH MUCH lighter than the stock rods and pistons... A balanced engine will last longer and run smoother than a non-balanced engine....Just do it man...don't take any short cuts...

    Chris
     
  5. bablazer73

    bablazer73 1/2 ton status

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    i'm gonna have to agree. gotta balance them.
     
  6. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Hmmm......

    So ya'all think I should get it balanced? [​IMG] lol...J/K.

    The shop I called listed the same stuff that tarussel listed in his post, almost to the letter. Including harmonic balancer bolt and washer, and flywheel bolts.

    Seriously though, Thanks for the input- Pretty much confirming what I already thought. /forums/images/graemlins/thumb.gif

    Anyone else?
     
  7. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Ok Joe, just as mentioned above, it is a good idea to balance an engine in which any of the original rotating assembly has been changed. An engine from the factory comes balanced to within 4 grams or so but in the aftermarket world they are balanced to within usually a 1/4 gram or so. Now if you start swapping parts around from other engines then there is a chance that the balancing of the rotating assembly will change. Now you mentioned about them having to take apart the pistons and rods in order to balance them and then reconnect them when done. You almost never on a pressed type piston can ever take them apart and reuse the pistons, there is always that 1 exception when it does work however. Here is what I think you should do. Ask the machine shop that is going to balance it for you if they could just weigh and balance each piston/rod assembly rather than taking them apart. Before anyone comes jumping to any conclusions you have to remember that the engine will still be balanced by doing it this way but there is no risk to damaging a piston and then having to replace 1 or all of them. When an engine is balanced by an independent shop the rods are actually balanced between the small pin end and also the large journal end. For those who do not understand what I am talking about I will explain it for you. Lets start at the small pin end of the rods, we weigh each rod and find the lightest small end then make all others the same weight, now we find the lightest large journal end and make all the others the same weight, now the rods are balanced but also from end to end not just the whole rod sitting on a scale. The same goes for the pistons, the lightest piston is found then all the rest are machined to match. Now you add the weight of 1 piston, 1 rod, 1 set of rings, and 1 rod bearing togther. Now you need to make a bob weight that matches this amount and attach it to the crank and then spin the crank on the balancing machine and add or subtract weight to the appropiate places. Once all this is done if it is an internally balanced engine you spin the flexplate/flywheel by itself and zero balance it. The same is done for the harmonic balancer. Now the balancing is done. I know this is a long reply, but some people have no idea of how an engine is balanced and might find it interesting to know.
     
  8. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    [ QUOTE ]
    Ok Joe, just as mentioned above, it is a good idea to balance an engine in which any of the original rotating assembly has been changed. An engine from the factory comes balanced to within 4 grams or so but in the aftermarket world they are balanced to within usually a 1/4 gram or so. Now if you start swapping parts around from other engines then there is a chance that the balancing of the rotating assembly will change. Now you mentioned about them having to take apart the pistons and rods in order to balance them and then reconnect them when done. You almost never on a pressed type piston can ever take them apart and reuse the pistons, there is always that 1 exception when it does work however. Here is what I think you should do. Ask the machine shop that is going to balance it for you if they could just weigh and balance each piston/rod assembly rather than taking them apart. Before anyone comes jumping to any conclusions you have to remember that the engine will still be balanced by doing it this way but there is no risk to damaging a piston and then having to replace 1 or all of them. When an engine is balanced by an independent shop the rods are actually balanced between the small pin end and also the large journal end. For those who do not understand what I am talking about I will explain it for you. Lets start at the small pin end of the rods, we weigh each rod and find the lightest small end then make all others the same weight, now we find the lightest large journal end and make all the others the same weight, now the rods are balanced but also from end to end not just the whole rod sitting on a scale. The same goes for the pistons, the lightest piston is found then all the rest are machined to match. Now you add the weight of 1 piston, 1 rod, 1 set of rings, and 1 rod bearing togther. Now you need to make a bob weight that matches this amount and attach it to the crank and then spin the crank on the balancing machine and add or subtract weight to the appropiate places. Once all this is done if it is an internally balanced engine you spin the flexplate/flywheel by itself and zero balance it. The same is done for the harmonic balancer. Now the balancing is done. I know this is a long reply, but some people have no idea of how an engine is balanced and might find it interesting to know.

    [/ QUOTE ]


    Right on Scott. I was hoping your words would make it in here. /forums/images/graemlins/thumb.gif

    I guess the next issue is to figure out what to do about the pistons- Get new ones, or ask the machine shop about leaving them attached to the rods. I've also got to decide if I want to remove the heads and take the block to be hot tanked and rehoned, bored if needed. Hmmm.. /forums/images/graemlins/thinking.gif Lots of thinking to do..
     
  9. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    [Scott lays some serious science on the crowd about engine balancing, and the steps involved]


    .......suddenly $175 doesn't sound so unreasonable! /forums/images/graemlins/grin.gif
     
  10. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Hey Joe, the heads need to come off in order for you to get the pistons out. I highly recommend that you hone the cylinders and boil the block clean at the minimum. Another thing I would have done is to have the machine shop check the sizing of the big ends of your rods to make sure they are round and within specifications, if not then they will need to be resized.
     
  11. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Hmm....More food for thought. /forums/images/graemlins/thinking.gif

    Thank you Scott.
     

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