Question for Joe Lucia: Alternatives to '62-'68 GM 8" balancer, part number 3817173

[Joe L.]

Re: Question for Joe Lucia: Alternatives to '62-'68 GM 8" balancer, part number 3817

hi joe, do we know when Chevy went to the center bolt crankshaft?

Frank------

For small blocks it began with the 1962 models equipped with the 340 and 360 HP engines and the 3817173 balancer and continued through 1968 for SHP engines. In 1969 and thereafter all small blocks got the center bolt. Big blocks always had the center bolt from 1965 thru 1974 and regardless of engine.

[Frank H.]

Re: Question for Joe Lucia: Alternatives to '62-'68 GM 8" balancer, part number 3817

thanks joe, that's very helpful.

Frank------

For small blocks it began with the 1962 models equipped with the 340 and 360 HP engines and the 3817173 balancer and continued through 1968 for SHP engines. In 1969 and thereafter all small blocks got the center bolt. Big blocks always had the center bolt from 1965 thru 1974 and regardless of engine.

[David L.]

Re: Question for Joe Lucia: Alternatives to '62-'68 GM 8" balancer, part number 3817

What I don't understand is the meaning of "GB" and "2" near the casting number and the stamped "F K 6". Can anybody help out here? Is this unit for '67-'68 350 non-corvette engine only? I know the 350 was introduced in 1967 for the Camaro SS only and Corvette did not get the 350 until 1969.

Rocco,
I have an original Harmonic Balancer for 1969 & 1970 Camaro SS350 models with L48 300 H.P. engine. The numbers "7704" and "B 9 F" are stamped on the front. I believe that the "B" represents February and the number "9" represents 1969. The letter "F" might represent the manufacturer or maybe Flint, MI. The casting number on the back side is "3896966" along with the letters "GB" inside an oval and the number "3". The balancer measures 8" in diameter and the thickness measures about 1.33". The balancer weight is about 10 1/4 lbs.
My 1969 Chevrolet Parts Catalog (Oct. 1968) lists GM # 3947704 in Gr. 0.659 for the 69 ALL w/4BC (350).
My 1970 Chevrolet Parts Catalog (Jan. 1970, for 1970 Chevrolet models only) lists GM # 3947704 in Gr. 0.659 for the 69-70 ALL w/4BC (350)(exc. Sp. H/Per.). Attached are 2 photos.

I also have many 6" harmonic balancers including one that is stamped "E 6 F" (May 1966) from a 1966 Chevrolet 327 with casting date May 18, 1966 and assembly date May 21, 1966.

Dave

[Joe R.]

Re: Question for Joe Lucia: Alternatives to '62-'68 GM 8" balancer, part number 3817

I have some more information on the "mystery balancer" that I described in post #12. Since these are very inexpensive on ebay, I bought one to study.

I'm hoping that with the following info and photos, Joe Lucia can help identify the original application for this unusual configuration.

The construction of this balancer differs from the construction of the 1.25" wide and 1.70" wide 8" diameter versions that we have been discussing:

1) It uses the hub from the 1.25" balancer (casting 3896966)

2) The inertia ring is the same 1.70" nominal width as the original 1962-1968 #3817173 and the follow-on variations of that balancer that used a nominal 1.70" wide hub.

3) The reason that a wide inertia ring can be installed on a narrower hub is that only the first 1.25" of the inertia ring width is sized to mate with the 1.25" wide hub. The remaining width of the inertia ring consists of a flange that extends the outer surface of the inertia ring to the nominal 1.70" width of the #3817173.

4) The timing mark on the inertia ring is approximately 50 degrees away from the keyway. This is far different from the nominal 0 degree difference found on 1962-1968 Corvette small block balancers, and the nominal 10 degree difference found on the 1969-up Corvette small block balancers.


What I find intriguing about this balancer is that when it is installed on the engine, the wide inertia ring makes it look like the other "wide" balancers that started in 1962 with the #3817173. Granted, the difference can be detected using a mirror or getting under the car, but it's not obvious to the casual observer.

Used versions of this balancer are available on ebay for less than $50 (this one cost $34 with free shipping). This provides a much less expensive core for rebuilding compared to the #3817173 and its derivatives.

In theory, this balancer could be rebuilt with the timing mark located in the correct position for 1962-1968.

Here's what I see in the following photos:

Stamped part number derivative: 8652
Stamped date code: 229 78
Hub casting number: 3896966 (6272222 has been observed on other units)
Timing mark is about 50 degrees offset from the keyway

[Joe L.]

Re: Question for Joe Lucia: Alternatives to '62-'68 GM 8" balancer, part number 3817

I have some more information on the "mystery balancer" that I described in post #12. Since these are very inexpensive on ebay, I bought one to study. I'm hoping that with the following info and photos, Joe Lucia can help identify the original application for this unusual configuration. The construction of this balancer differs from the construction of the 1.25" wide and 1.70" wide 8" diameter versions that we have been discussing: 1) It uses the hub from the 1.25" balancer (casting 3896966) 2) The inertia ring is the same 1.70" nominal width as the original 1962-1968 #3817173 and the follow-on variations of that balancer that used a nominal 1.70" wide hub. 3) The reason that a wide inertia ring can be installed on a narrower hub is that only the first 1.25" of the inertia ring width is sized to mate with the 1.25" wide hub. The remaining width of the inertia ring consists of a flange that extends the outer surface of the inertia ring to the nominal 1.70" width of the #3817173. 4) The timing mark on the inertia ring is approximately 50 degrees away from the keyway. This is far different from the nominal 0 degree difference found on 1962-1968 Corvette small block balancers, and the nominal 10 degree difference found on the 1969-up Corvette small block balancers. What I find intriguing about this balancer is that when it is installed on the engine, the wide inertia ring makes it look like the other "wide" balancers that started in 1962 with the #3817173. Granted, the difference can be detected using a mirror or getting under the car, but it's not obvious to the casual observer. Used versions of this balancer are available on ebay for less than $50 (this one cost $34 with free shipping). This provides a much less expensive core for rebuilding compared to the #3817173 and its derivatives. In theory, this balancer could be rebuilt with the timing mark located in the correct position for 1962-1968. Here's what I see in the following photos: Stamped part number derivative: 8652 Stamped date code: 229 78 Hub casting number: 3896966 (6272222 has been observed on other units) Timing mark is about 50 degrees offset from the keyway

Joe------- So far, I've been unable to find anything on it. My guess is that it's for a marine application, probably Mercury Marine using a core Chevrolet engine.

[Joe R.]

Re: Question for Joe Lucia: Alternatives to '62-'68 GM 8" balancer, part number 3817

Joe------- So far, I've been unable to find anything on it. My guess is that it's for a marine application, probably Mercury Marine using a core Chevrolet engine.

Hi Joe:

Thanks for looking into this. Whatever the original application was, there are a lot of these on ebay, so it was not a low-volume part. On ebay, if you do a search on 3896966, there are currently 39 balancers listed. Many ebay sellers think that the hub casting number is the GM part number (which it apparently was, very briefly), but that same hub casting was used for at least three different types of GM balancers.

For each ebay listing of a so-called 3896966 balancer, it's necessary to examine the photos to see which of the three balancers is being offered.

1) The 1.25" wide balancer used on 350 engines (23 listed)
2) Some 400 balancers where the balance weight was incorporated into the intertia ring (10 listed)
3) This "mystery balancer" that has a 1.7" wide inertia ring on the 1.25" hub (6 listed)

Given that the timing mark on the mystery balancer is in a unique position that differs from the nominal 0 degree and nominal 10 degree positions that we are most familiar with, there must have been something unusual about the application of the mystery balancer that required a unique location.

I agree that a marine application could be one explanation, but I'm wondering whether a truck application might also be a candidate. There were probably a lot more trucks made with small block engines than boats.

[Joe L.]

Re: Question for Joe Lucia: Alternatives to '62-'68 GM 8" balancer, part number 3817

Hi Joe:

Thanks for looking into this. Whatever the original application was, there are a lot of these on ebay, so it was not a low-volume part. On ebay, if you do a search on 3896966, there are currently 39 balancers listed. Many ebay sellers think that the hub casting number is the GM part number (which it apparently was, very briefly), but that same hub casting was used for at least three different types of GM balancers.

For each ebay listing of a so-called 3896966 balancer, it's necessary to examine the photos to see which of the three balancers is being offered.

1) The 1.25" wide balancer used on 350 engines (23 listed)
2) Some 400 balancers where the balance weight was incorporated into the intertia ring (10 listed)
3) This "mystery balancer" that has a 1.7" wide inertia ring on the 1.25" hub (6 listed)

Given that the timing mark on the mystery balancer is in a unique position that differs from the nominal 0 degree and nominal 10 degree positions that we are most familiar with, there must have been something unusual about the application of the mystery balancer that required a unique location.

I agree that a marine application could be one explanation, but I'm wondering whether a truck application might also be a candidate. There were probably a lot more trucks made with small block engines than boats.

Joe------


I've checked truck applications and I can't find it.

[Joe R.]

Re: Question for Joe Lucia: Alternatives to '62-'68 GM 8" balancer, part number 3817

Joe------


I've checked truck applications and I can't find it.

Thanks Joe for checking this. I guess the mystery will continue.