Internal or external balance??
Thread Starter
Drifting
Joined: Apr 2008
Posts: 1,305
Likes: 2
From: Lewisburg WV
Internal or external balance??
I have a 1979 L-82 with a 350 automatic. I need to install a new flex plate. I would like to purchase an aftermarket heavier duty than original. Flex plates are listed by Summit and Jegs for internal or external balanced engines. How do you know if your engine is internally or externally balanced?
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Internal or external balance??
If it's really a 350 with a stroke of 3.48 inches, it is internally balanced. To verify, the GM balancer will be machined smooth all around the circumference. If it is stroked 383, 400, or 406, that uses a 3.75 inch stroke, it is typically externally balanced (unless very heavy mallory metal has been embedded into the crank's counterweights, which is very expensive).
An external balance harmonic damper for the 383, 400 or 406 SBC can be identified by a depressed zone with a rough as cast finish over a portion of its circumference; the remainder of the circumference will be machined smooth like the balancers for 350 and smaller SBCs. The imbalance of this damper contributes to the balance of the counterweights to put the engine in proper balance.
Typically, the flex plate for 383s, 400s, and 406s is also "external" balanced, and can be spotted by noting an counterweight welded to the flexplate.
Cheers,
Larry
An external balance harmonic damper for the 383, 400 or 406 SBC can be identified by a depressed zone with a rough as cast finish over a portion of its circumference; the remainder of the circumference will be machined smooth like the balancers for 350 and smaller SBCs. The imbalance of this damper contributes to the balance of the counterweights to put the engine in proper balance.
Typically, the flex plate for 383s, 400s, and 406s is also "external" balanced, and can be spotted by noting an counterweight welded to the flexplate.
Cheers,
Larry
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
If it's really a 350 with a stroke of 3.48 inches, it is internally balanced. To verify, the GM balancer will be machined smooth all around the circumference. If it is stroked 383, 400, or 406, that uses a 3.75 inch stroke, it is typically externally balanced (unless very heavy mallory metal has been embedded into the crank's counterweights, which is very expensive).
An external balance harmonic damper for the 383, 400 or 406 SBC can be identified by a depressed zone with a rough as cast finish over a portion of its circumference; the remainder of the circumference will be machined smooth like the balancers for 350 and smaller SBCs. The imbalance of this damper contributes to the balance of the counterweights to put the engine in proper balance.
Typically, the flex plate for 383s, 400s, and 406s is also "external" balanced, and can be spotted by noting an counterweight welded to the flexplate.
Cheers,
Larry
An external balance harmonic damper for the 383, 400 or 406 SBC can be identified by a depressed zone with a rough as cast finish over a portion of its circumference; the remainder of the circumference will be machined smooth like the balancers for 350 and smaller SBCs. The imbalance of this damper contributes to the balance of the counterweights to put the engine in proper balance.
Typically, the flex plate for 383s, 400s, and 406s is also "external" balanced, and can be spotted by noting an counterweight welded to the flexplate.
Cheers,
Larry
Team Owner
Joined: Oct 2004
Posts: 23,831
Likes: 10
From: Springfield MO
St. Jude Donor '07
There are new 383 and 400 cranks made that are internally balanced.
