Harmonic balancer differences?
Thread Starter
Racer
Joined: May 2005
Posts: 479
Likes: 95
From: Boca Raton FL
Harmonic balancer differences?
What is the difference between a 1963-65 327/300 balancer and the one used in 1966? The parts manual lists different part numbers. Both balancers are 6" in diameter. Is it ok to use the 65 balancer on a 66?
Race Director
Joined: Mar 2001
Posts: 14,642
Likes: 4,689
From: Mustang OK
2026 Corvette of the Year Finalist - Modified
2025 c1 of the Year - Modified Winner
2024 C1 of the Year Finalist - Modified
2023 C1 of the Year Finalist - Modified
2015 C1 of the Year Finalist
The most significant change that occured to balancers was between 68-69. The timing mark on 68-earlier balancers is in-line with the crankshaft keyway. In 69, the timing mark was rotated about 10-12deg toward the Advance (A) mark. As a result, the timing cover with the correct corrosponding timing tab must also be used. The hard one to find is a 62-68 timing cover for an 8in balancer!!!
So, to answer your question, as long as you stay within the same family of balancer/timing cover, you'll be just fine. From my viewpoint, a 6in balancer is a 6in balancer and an 8in balancer is an 8in balancer (with its corrosponding timing cover).
As an example, if you were to install a 1975 8in balancer from a 350 engine onto a 1963 327 (or even a 283), you would just need to also use the timing cover from the '75 350.
So, to answer your question, as long as you stay within the same family of balancer/timing cover, you'll be just fine. From my viewpoint, a 6in balancer is a 6in balancer and an 8in balancer is an 8in balancer (with its corrosponding timing cover).
As an example, if you were to install a 1975 8in balancer from a 350 engine onto a 1963 327 (or even a 283), you would just need to also use the timing cover from the '75 350.
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
That's fine for the timing aspect. I wouldn't think it would be wise to disregard the time/effort Chevrolet put into tuning balancers to individual applications. You can cause yourself some grief with crankshaft cracking problems.
Race Director
Joined: Mar 2001
Posts: 14,642
Likes: 4,689
From: Mustang OK
2026 Corvette of the Year Finalist - Modified
2025 c1 of the Year - Modified Winner
2024 C1 of the Year Finalist - Modified
2023 C1 of the Year Finalist - Modified
2015 C1 of the Year Finalist
No argument with that, I was only giving an example of the matching of a balancer/timing cover. Of course, if an engine is a "built" engine, then what balancer do you select????
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
That's a very good question and one I'm not prepared to debate. I've asked any number of engineers over the years how a harmonic balancer is tuned to the engine. Most reponses were just a shrug of the shoulders. I wish somebody could answer that in a manner everyone could understand.
One response I got from factory engine resident engineer, if you can believe this. Harmonics? Hell, I can't even play a ukelele!
I don't know how it's done, I just know the consequences of using the wrong one from the school of hard knocks.
Last edited by MikeM; Jan 23, 2008 at 01:39 PM.
Burning Brakes
Joined: Mar 2001
Posts: 1,203
Likes: 147
From: dalton ma
How about this theory. 8" balancers were used on the more HP engines with somewhat more radical cams. I think the bigger/heavier balancers were used to "help" the hotter engines move out from a standstill more smoothly. Bob
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
I don't know the scientific answer either, but the GM drawings for balancers all show that the assembly must be tuned for 165-180 cycles per second at 150*F. Since a V-8 engine fires four times per revolution (and a torsional damper damps individual firing impulses), that would indicate that the dampers are tuned for an engine speed of about 2800 rpm.
2800 rpm = 46 rev. per second = 23 full V-8 firing cycles = 184 cycles per second.
The drawing also states that the polar moment of inertia of the outer ring must be 0.286 inch-pounds per second squared, but I've been out of college for too many years to deal with that.
2800 rpm = 46 rev. per second = 23 full V-8 firing cycles = 184 cycles per second.
The drawing also states that the polar moment of inertia of the outer ring must be 0.286 inch-pounds per second squared, but I've been out of college for too many years to deal with that.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
But, since I never got past the 8th grade, I'm not prepared to deal with it either.
I've told you way more than I know.
Race Director
Joined: Nov 2000
Posts: 10,349
Likes: 674
From: Beverly Hills (Pine Ridge) Florida
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
