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Old 07-12-2013, 03:53 AM   #1
Ze2222
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Default Engine balance question.

Hi guys. I have a little issue and was looking for some advice/opinions. Now here is the just of it.
I bought a used 351w, stroked to 392. The guy I bought it from had a flexplate for a c6.
Now heres the kicker, he says the engine balance is 50oz. Now from researching I found out it should be 28oz.
So herein I take off the oil pan and inspect and can see slugs in the web of the cranks which leads me to believe custom balancing.
So I will be taking his word and i'm using a 50oz flexplate for a c4.
I'm going to run the engine with the trans off. Now will I see if the motor is out of balance. I've never seen one. Or will this be a silent killer? lol.
Basically will I be able to tell if put the wrong flexplate?
I hope someone chimes in cause i'm going through with this anyways lol and would like to know my ramifications.
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Old 07-12-2013, 02:14 PM   #2
Ze2222
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no one?
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Old 07-12-2013, 03:12 PM   #3
dawson1112
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Sounds like this engine has been taken to a shop and internally balanced . I would stick with what was on the engine . Go with the 50oz

The guy you got the engine probly knows exactly what it was balanced at.
It is not uncommon , and probly a very good idea when stroking these to have them internally balanced.

As far as being able to tell if you have the correct balance flexplate No. You could not tell just by running the engine . You have to trust the previous owner.
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Old 07-12-2013, 03:40 PM   #4
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Quote:
Originally Posted by Ze2222 View Post
Now heres the kicker, he says the engine balance is 50oz. Now from researching I found out it should be 28oz.
So herein I take off the oil pan and inspect and can see slugs in the web of the cranks which leads me to believe custom balancing.
So I will be taking his word and i'm using a 50oz flexplate for a c4.
I'm going to run the engine with the trans off. Now will I see if the motor is out of balance. I've never seen one. Or will this be a silent killer? lol.
Basically will I be able to tell if put the wrong flexplate?
My 393 is internally balanced (best decision if racing, imo). If you fire that thing up with the wrong type of balance, your motor will head south pretty quick. What balancer is on the front of the engine? Its technically called a harmonic damper, because it absorbs any engine vibrations produced from slinging around the rotating assembly. Just because there are slugs in the crank doesn't mean its internally balanced, you could have a sh*tty chinese crankshaft the shop couldn't get balanced without mallory metal. If you want to be 100% on it, which you should if building any type of performance motor, disassemble the rotating assembly and take it to a balancing shop and have them determine it. This is the only real way to know, unless you truly trust the guy you bought it from. I wouldn't.

Trust me on this balancing thing. I went through the same scenario about 6 months ago.
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Last edited by Duncan_GT; 07-12-2013 at 03:42 PM.
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Old 07-23-2013, 12:41 PM   #5
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well you could take his word on it....but i agree with the above..if I had any doubt i would take it apart and have it zero balanced..the peace of mind alone would be worth the cost..
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Old 06-07-2014, 06:31 AM   #6
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Hmmmmm! Well the only 50oz imbalance ford is the 5.0l 302.... once you got stroker or 351 you have a 28oz imbalance but if you have a forged crank you have the option of internal balance which is what you are explaining with metal welded into a drilled recess in the counter weight which means you run a balancer and plate with no imbalance.
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Old 06-07-2014, 06:33 AM   #7
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Sorry for the double post. You WILL notice as soon as you crank it if its out of balance the engine will have a wicked vibration that shakes the car!
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Old 06-09-2014, 07:59 AM   #8
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Call the guy back and ask who did the balance job call them up and ask them if they have the balance sheet. Most all shops keep a sheet.
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Old 06-09-2014, 07:59 AM
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