Difference between an internal and external balanced crank?
Thread Starter
Instructor
Joined: Jun 2002
Posts: 231
Likes: 0
From: 80/680 junction Ca.
Difference between an internal and external balanced crank?
What are the physical differences between internal and external balanced cranks?
I know the difference between the two methods.
I'm just not clear on the reasons, also the pros and cons.
Set a stock 400 crank next to say a Scat internal balanced crank with the same journal sizes and stroke. Are the physical weight of the counter weights different?
Is it not possible to get a stock 400 cast crank to balance without the addition of external weight?
I know the difference between the two methods.
I'm just not clear on the reasons, also the pros and cons.
Set a stock 400 crank next to say a Scat internal balanced crank with the same journal sizes and stroke. Are the physical weight of the counter weights different?
Is it not possible to get a stock 400 cast crank to balance without the addition of external weight?
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
The reason for an externally balanced crank is that with the length of the stroke involved, there isn't enough weight far enough from the centerline of the crank, to offset the weight of the reciprocating assembly. The term "externally balanced" is somewhat of a misnomer. Weight is added externally to the damper and/or the flywheel, but the actual balancing takes place internally just as it does on an internally balanced engine.
It IS possible to get a stock 400 cast crank to balance without the addition of external weight. It is done by adding INTERNAL weight. By drilling holes in the counterweights of the crankshaft and filling them with metal that is more dense and heavier that the iron/steel that was removed. It is called Mallory or just heavy metal. The extra machining and the expensive Mallory heavy metal can make internally balancing an expensive proposition. The advantage to internal balancing is to have the weight directly over the counter balance, rather than have it cantilevered outside of the block, adding somewhat of a side stress to the crank and bearings. External balancing isn't as horrible as some would lead you to believe. Many engines other than the SBC 400 (and BBC 454) are externally balanced.
RACE ON!!!
It IS possible to get a stock 400 cast crank to balance without the addition of external weight. It is done by adding INTERNAL weight. By drilling holes in the counterweights of the crankshaft and filling them with metal that is more dense and heavier that the iron/steel that was removed. It is called Mallory or just heavy metal. The extra machining and the expensive Mallory heavy metal can make internally balancing an expensive proposition. The advantage to internal balancing is to have the weight directly over the counter balance, rather than have it cantilevered outside of the block, adding somewhat of a side stress to the crank and bearings. External balancing isn't as horrible as some would lead you to believe. Many engines other than the SBC 400 (and BBC 454) are externally balanced.
RACE ON!!!
