67 low HP 3896903 balancer and 3896904 balancer question

[David L.]

Does anyone know what the difference is between the 1967 Corvette low HP 6 1/8" balancer (GM # 3896903) and the 3896904 balancer (also 6 1/8")? The 3896904 balancer did not appear in the Chevrolet parts catalogs until about Sept. 1971 and is used as a replacement for the 57-61 Corvettes and 62-65 Corvettes (exc. Sp. H/Per., F.I., 396).

In each of the 2 photos enclosed the balancer on the left is stamped "H6903" and the balancer on the right is stamped "6904".

Both balancers measure 6 1/8" in diameter and weight about 4.5 lbs. To me they appear to be identical (except for the balancing weights and balancing holes) but have different part numbers and are for different applications.

[Timothy B.]

Re: 67 low HP 3896903 balancer and 3896904 balancer question

David,

The answer to your question may be in the archives, I remember a thread about this a few years ago. It's either the harmonic balancing of the damper or the inside diameter of the crank snout for press fit verses snug fit with the bolt to retain.

[Joe L.]

Re: 67 low HP 3896903 balancer and 3896904 balancer question

Does anyone know what the difference is between the 1967 Corvette low HP 6 1/8" balancer (GM # 3896903) and the 3896904 balancer (also 6 1/8")? The 3896904 balancer did not appear in the Chevrolet parts catalogs until about Sept. 1971 and is used as a replacement for the 57-61 Corvettes and 62-65 Corvettes (exc. Sp. H/Per., F.I., 396).

In each of the 2 photos enclosed the balancer on the left is stamped "H6903" and the balancer on the right is stamped "6904".

Both balancers measure 6 1/8" in diameter and weight about 4.5 lbs. To me they appear to be identical (except for the balancing weights and balancing holes) but have different part numbers and are for different applications.

Dave------


They are configurationally identical. The difference is in the "tuning". I have the blueprints for both balancers around here somewhere. I think I may have previously posted them.

I used to think that the difference had to do with ID size of the crank snout hole but I was wrong about that.

[David L.]

Re: 67 low HP 3896903 balancer and 3896904 balancer question

Joe,

I just measured the I.D. of each of the two balancers and they both measure 1.251" as best as I could measure them.

On the back side the lip of the rubber like cushion on the 6904 balancer is thicker. The front sides look the same. I assume this rubber like cushion affects the "tuning".

Dave

[Michael H.]

Re: 67 low HP 3896903 balancer and 3896904 balancer question

On the back side the lip of the rubber like cushion on the 6904 balancer is thicker. The front sides look the same. I assume this rubber like cushion affects the "tuning".

Dave

There may be a number molded in the elastomer, similar to one in the elastomer of an 8" damper. I wonder if the number will be different between your two dampers indicating different properties?

Pic below shows numbers in elastomer just to the left of the hub casting number.

[David L.]

Re: 67 low HP 3896903 balancer and 3896904 balancer question

The are not any numbers on the elastomers of either balancer.

[Joe L.]

Re: 67 low HP 3896903 balancer and 3896904 balancer question

Joe,

I just measured the I.D. of each of the two balancers and they both measure 1.251" as best as I could measure them.

On the back side the lip of the rubber like cushion on the 6904 balancer is thicker. The front sides look the same. I assume this rubber like cushion affects the "tuning".

Dave

Dave------

After I dispensed with the notion that the ID of the snout hole was the difference between the balancers, I figured that the elastomer component had to be what varied between the two balancers. However, the drawings for the two balancers calls out the GM part number for each of the balancer components (i.e. hub, ring, and elastomer). The part numbers for each component are shown as being the same. So, how the difference in tuning is achieved, I do not know.

[David L.]

Re: 67 low HP 3896903 balancer and 3896904 balancer question

There may be a number molded in the elastomer, similar to one in the elastomer of an 8" damper. I wonder if the number will be different between your two dampers indicating different properties?

Pic below shows numbers in elastomer just to the left of the hub casting number.

I have a NOS 3896903 balancer (stamped "H6903") made on the 225th day of 1982 (stamped "225 82") that has a molded number on the elastomer as follows:
"34 0C 3965".