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Do I need to balance the crank?

67charger383

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I'm getting my 383 bored 30 over and the machine shop is telling me I need to have my crank balanced. It is a '67 forged crank and will have TRW flat top pistons.

Do I really need to get it balanced? The crank is in perfect condition and I don't have a huge budget.
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You should always have the rotating assembly balanced. There is no way I would build it without knowing its good to go.
 
The only way you would get away without is if the pistons, and the rods weighed exactly the same as what was in there last time it was balanced (or originally built). I'd say you need to check the bobweight with the TRW pistons and balance accordingly.
 
The only way you would get away without is if the pistons, and the rods weighed exactly the same as what was in there last time it was balanced (or originally built). I'd say you need to check the bobweight with the TRW pistons and balance accordingly.

The rods will be stock with TRW heads.
 
How close do you think the factory balances hundreds of thousands of engines engines ?? Do you see any grinding marks on stock rods indicating the factory balanced them ??

For a basically stock rebuild, save yourself the money and skip the balancing.
 
Adding onto what Lefty71 said. If your using the same rods and just changing pistons, weigh the new piston, pin, and ring stack. If the weight difference is about 15 grams or less, my advice is no need to rebalance. I've used that method for years on oval track engines that would see some sustained rpm up to 9,000 rpm without a vibration issue noticed, or noticable problems.
I've wondered how far out you could go on a drag type engine that cycles through the rpm fast, before the out of balance becomes noticeable. Just never got brave enough to push it and have a comeback on a job. Maybe someone else on here that has assembled a lot of engines and balances cranks could chime in.
Remember that if your close on weight you have the piston pin weight to juggle around. Buying new pins would be cheaper than the balance cost. Just be sensible with the pin weight and don't use some really light thin wall pin to get there as that piston is a rather heavy slug.
 
How much rpm do you plan to turn and do you think the factory balance was good up to say 6000 rpm? TRW pistons are probably not going to be the same as the stock pistons either.......

Adding onto what Lefty71 said. If your using the same rods and just changing pistons, weigh the new piston, pin, and ring stack. If the weight difference is about 15 grams or less, my advice is no need to rebalance. I've used that method for years on oval track engines that would see some sustained rpm up to 9,000 rpm without a vibration issue noticed, or noticable problems.
I've wondered how far out you could go on a drag type engine that cycles through the rpm fast, before the out of balance becomes noticeable. Just never got brave enough to push it and have a comeback on a job. Maybe someone else on here that has assembled a lot of engines and balances cranks could chime in.
Remember that if your close on weight you have the piston pin weight to juggle around. Buying new pins would be cheaper than the balance cost. Just be sensible with the pin weight and don't use some really light thin wall pin to get there as that piston is a rather heavy slug.
How many laps did your oval track engines last?
 
Cranky,
Do you mean the total amount of laps before seen again, or how long they ran as in there's going to be a problem ?
 
Cranky,
Do you mean the total amount of laps before seen again, or how long they ran as in there's going to be a problem ?
Weeeel, most drag race engines that we build around here don't see 9k rpm....and 120 grams total if that's what you get is a lot if you're turning 9k. Just wondering how long an engine with that much imbalance will go turning that kind of sustained rpm.
 
The rods will be stock with TRW


You might luck out. If the TRW flat tops are replacement pistons, not racing pistons, then the weight may already be close enough to use as is. Something such as Keith Black hypereutetic cast would be way lighter and definately require lightening on the crank. Do you already own the pistons?? Have a catalog number?? I think I may have some OEM 383 pistons to weigh for comparison if yours are already gone. HTH, Lefty71
 
Weeeel, most drag race engines that we build around here don't see 9k rpm....and 120 grams total if that's what you get is a lot if you're turning 9k. Just wondering how long an engine with that much imbalance will go turning that kind of sustained rpm.
I don't know why a person would use this forum to insinuate that others are doing things completely wrong, to make themselves look superior in their mind. I never said cranks were balanced with a reciprocating factor that off by 15 grams on a regular basis. Never said that it was a drag engine turning 9k either, was small block Chevy sprint engines. Different engine builders out there balance between 48-51 percent, and feel that works best for them depending on application. Does that make everyone else wrong too ?
I'm a member here to see others nice projects, learn, and if possible contribute in a positive way to help others in areas that I do have experience in. Not give info that I've heard or been told without doing it myself. I think most on here would like to help others no matter how big or small their contribution is without sarcasm if you don't have all the facts.
 
If a motor is being rebuilt with OEM replacement pistons (Sealed Power, Badger, Silvolite, etc..) and other parts, it is not necessary to rebalance the motor. OEM replacement parts are made to match the OEM requirements for that exact reason. Now, if you are using Weisco, Ross, JE, etc.. pistons, you will need to rebalance. If you are using aftermarket rods, you will need to rebalance. An aftermarket crank will also require a rebalance. Seeing how TRW has been gone since the '80s IIRC, getting good info on them will be hard. Someone made a good suggestion to have the old pistons weighed, and make the TRW pistons match the average old weight and you should be fine. But, if you want to rebalance the entire rotating assy, then go ahead.
 
Well, I would not want to drive a grenade around hoping that all that money I just spent on a rebuild doesnt fly out the side of my block. I think its worth the extra cost to be sure its balanced. However, Its your car, your engine and your choice.
 
I'm getting my 383 bored 30 over and the machine shop is telling me I need to have my crank balanced. It is a '67 forged crank and will have TRW flat top pistons.

Do I really need to get it balanced? The crank is in perfect condition and I don't have a huge budget.View attachment 880490

It's a good idea if you plan to keep the car/engine. Not sure what they charge for the balance job, but usually it is worth doing it once the right way, then having to do it twice.
 
just because you change pistons is not the reason to re-balance
it's only if the weights change
and by a lesser amount for a high rpm motor
hyd lifter motor they can be off quite a bit and were from the factory
now are they more weight or less weight
would the new build be overballanced or underballanced
one makes more difference than the other
ps lighter is better
 
Did you tell the machine shop to hold off while you consult an internet forum? They love that:rolleyes:
Really though, they have your engine, they know what parts are being used and the possible weight changes...if you know all the particulars yourself and can select parts to avoid needing a balance job, go for it. Otherwise I would defer to your builder..(out here where nothing is cheap my last balance job cost $200.)
 
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I rebuilt a motor with Seal Power pistons without balancing. Ran it at the track a lot too. It was fine.
 
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