400 with unbalanced flywheel
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400's are external balanced, so you need an counterweighted or un-balanced flexplate. If you put an internal or neutral balanced flexplate on you would "feel" it. And it would do damage to your bearings. How long it would run I don't know.
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8,405 Posts
yes, since 400's are normally externally balanced (meaning the balance weight compensation is done on the balancer and flywheel) and the other smallblocks are internally balanced (crank is drilled for the reciprocating bob weight and flywheels are zero balanced) you'd have a balance mismatch and more than likely a noticeable vibration.
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yes you would FEEL it.... I have replace a couple of neutral balance flex plates that were installed by mistake on a 400.. You betcha.. you will feel it.. and so will the bearings if left unattended....
you need both a external balancer and a external balanced flex plate....if using a stock GM 400 crank
the flex plate has a rather large weight welded next to the ring gear(cant miss it)
the Balancer if in stock configuration has a deceive notch cut on the out side of the balance ring(easy to spot)....
on after market balancers the extra weight is often a bolt on...that weight is inside next to the hub.. you would have to view the back side of the balancer to see it...
you need both a external balancer and a external balanced flex plate....if using a stock GM 400 crank
the flex plate has a rather large weight welded next to the ring gear(cant miss it)
the Balancer if in stock configuration has a deceive notch cut on the out side of the balance ring(easy to spot)....
on after market balancers the extra weight is often a bolt on...that weight is inside next to the hub.. you would have to view the back side of the balancer to see it...
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TROUBLE! Thats what would happen!
It could break the housing of the transmission.
Vibration is the understatement!
Al
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438 Posts
Sorry about the hijack but I've always wondered, what was the purpose of making the 400 externally balanced? Did they NEED to or were they all just sitting around a table wondering how to screw with the consumer?
Follow up question, can you have a machine shop balance a 400 rotating assembly? If you do, then can you use a 350 balancer and flexplate?
Follow up question, can you have a machine shop balance a 400 rotating assembly? If you do, then can you use a 350 balancer and flexplate?
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Yes they can internally balance the 400 assembly. It would not be cheap because of the weights to be added.
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13,309 Posts
Has to do with the limited space of the SBC and metal density..and above all cost of the casting and machining....
Yes you can make a 400 a neutral balance.. by adding Mallory metal.. about 1.5 times the density of lead.... a 1.0oz slug last I heard was $75.00... but I could be way off on the cost...as I really dont recall
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15,966 Posts
Not enough room in the block for proper counter weight on crank.
I think it was cheep fix, same flywheel, flex-plate used on 454
Al
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15,966 Posts
or purchase a internal balanced 3.75 stroke crank!!!
And then all the bearing spacers!
never mind
, just add tungsten weights and have it balanced!:devil:AL
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13,309 Posts
dont for get the 6" rods for the added counter weight length there big buddy!or purchase a internal balanced 3.75 stroke crank!!!
And then all the bearing spacers!
never mind
AL
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A member a while back had a 454 in their car that kept breaking Muncie 4 speed tailhousings and losing driveshafts. He claimed the engine didn't shake, but would break parts within blocks of his house. He tried everything from the flywheel back knowing he had the right flywheel. When the engine was out to rebuild the pin o the crank was lft out and the flywheel with the weight was put in the wrong spot. He broke lots of parts before he found the problem.
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