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Subject: Harmonic balancer 7" vs. 8"

Original Message
Name: john
Date: May 03, 1998 at 16:03:54
Subject: Harmonic balancer 7" vs. 8"
What is the difference between the two, other than size ?
Which one is better to use with 406 sbc?


Response Number 1
Name: Mike
Date: May 03, 1998 at 16:43:04
Subject: Harmonic balancer 7" vs. 8"
That depends on a lot of things. 406 CI is what combination? Are you talking about GM parts? or after market. All GM small block balancers are interchangable EXCEPT for the 400 unit 6272225 (unbalanced) which can only be used on the 400 crank, can't use anything else. A 400 balancer must stay with a 400 crank.

There is difference in width too, the intermediate performance 350 balancer is 8" by 1&1/2" wide. The special high performance 302, 327, 350 have the largest balancer 8" by 1&3/4" wide. Also do not interchange balancers without checking the timing tag location on the timing cover in relation to the timing mark on the balancer. This is best done during engine assembly.

The 7" (actual 6&3/4" x 1&3/16") came on the 305, 327, 350.

Another 7" (actual 6&3/4" x 1&11/16" came on the 267 and 305.

Response Number 2
Name: John D. Holp
Date: May 04, 1998 at 06:47:14
Subject: Harmonic balancer 7" vs. 8"

I have a small 7" harmonic balancer that I took off of a 307 cid small block chevy. It is quite thin and small in diameter compared to the 350 and 305 balancers I have.

I have often wondered if one built a hot 350 with everything statically and dynamically ballanced if the eingine would rev quicker but be sufficiently dampened with this balancer.

Your thoughts?


Response Number 3
Name: John Ladd
Date: May 19, 1998 at 22:37:12
Subject: Harmonic balancer 7" vs. 8"
RE: John's response and question about omitting the balancer on a well balanced engine. DON'T DO IT!!! No matter how well the engine is balanced, there will be harmonic vibrations. The vibration dampener (it doesn't really BALANCE anything) is essential to keep the engine running happily and to avoid self-destruction.

Response Number 4
Name: Schurkey
Date: May 20, 1998 at 10:17:12
Subject: Harmonic balancer 7" vs. 8"
Thousands and thousands of years ago, GM built 283's with forged crankshafts. These units had no harmonic balancer until GM began producing cast cranks, and then I think every 283, forged or cast crank got a damper. This would have happened around '63 or '64 (?). I'm tempted to say that if it worked for GM, it could work for us. But I won't. It doesn't. I blew up a 283 about a month after replacing the original damper (it disintigrated ) and to this day I believe the two events were connected. (Chicken and Egg theory...)

The best way to go is the Fluidampr unit. Because the inertia ring is not actually attached to the hub, but "floats" in silicone "Jell-O" the crank can accelerate as if the balancer were much lighter. The hub can accelerate and "leave the inertia ring behind" At the same time, the vibrations are dampened by the ring and silicone as if it had a "bigger, meatier" damper. Best of both worlds.

John Ladd is correct that a damper doesn't balance anything...If the engine is internally balanced. 400 small blocks, 454 and 502 are externally balanced and the damper is counterweighted.

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