Original 1966 (only) 300 HP balancer dated May 1966

[David L.]

Enclosed are 4 photos of an original 1966 harmonic balancer (6 1/8" dia.) dated May 1966 (stamped "E 6 F" on the back side of the outer ring, photo #3). The "E 6" is the May 1966 date code and the letter "F" represents the manufacturer. The outer ring measures 3/4" in thickness where the front 1/2" machined surface measures 6.125" in diameter and the rear 1/4" cast surface measures 6.08" in diameter (see photo #2). This balancer was removed from a 1966 Chevrolet 327 engine (block casting # 3858180) stamped "T 0521 HAR" (May 21, 1966) on the front pad. I bought the entire engine back in the 1980's in a junk yard for $25 complete with carb., starter, flywheel, etc. where all the date codes matched up. Based on researching my many Chevrolet parts catalogs the GM part number for this balancer is 3883204 in Gr. 0.659. The 3883204 part number appears in only my 1966 Chevrolet Parts Catalog (effective Oct. 1965) and my 1966 Corvair-Chevy II-Chevelle Parts Catalog (effective Jan. 1966). The 3883204 balancer is a "one year deal" as it is not shown in my 1965 Chevrolet Parts Catalogs (Oct. 1964, Jan. 1965, and May 1965) and was discontinued in July 1966 according to Chevrolet Parts History and replaced with balancer # 3896903 (very similar in appearance, about 95%) which has been sold over the counter for many years.

Finally, here is my question.
Is there any owners of 1966 Corvettes w/300 HP engines that still have the original 6 1/8" diameter balancer balancer, and if so, is your balancer similar to the one that I have?

[Joe L.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

Enclosed are 4 photos of an original 1966 harmonic balancer (6 1/8" dia.) dated May 1966 (stamped "E 6 F" on the back side of the outer ring, photo #3). The "E 6" is the May 1966 date code and the letter "F" represents the manufacturer. The outer ring measures 3/4" in thickness where the front 1/2" machined surface measures 6.125" in diameter and the rear 1/4" cast surface measures 6.08" in diameter (see photo #2). This balancer was removed from a 1966 Chevrolet 327 engine (block casting # 3858180) stamped "T 0521 HAR" (May 21, 1966) on the front pad. I bought the entire engine back in the 1980's in a junk yard for $25 complete with carb., starter, flywheel, etc. where all the date codes matched up. Based on researching my many Chevrolet parts catalogs the GM part number for this balancer is 3883204 in Gr. 0.659. The 3883204 part number appears in only my 1966 Chevrolet Parts Catalog (effective Oct. 1965) and my 1966 Corvair-Chevy II-Chevelle Parts Catalog (effective Jan. 1966). The 3883204 balancer is a "one year deal" as it is not shown in my 1965 Chevrolet Parts Catalogs (Oct. 1964, Jan. 1965, and May 1965) and was discontinued in July 1966 according to Chevrolet Parts History and replaced with balancer # 3896903 (very similar in appearance, about 95%) which has been sold over the counter for many years.

Finally, here is my question.
Is there any owners of 1966 Corvettes w/300 HP engines that still have the original 6 1/8" diameter balancer balancer, and if so, is your balancer similar to the one that I have?

Dave-----


The only difference I can see between this balancer and the GM #3896903 is the as-cast portion of the rear of the perimeter of the balancer ring.

Note the balance weights in two of the holes on the balancer ring. These were installed at final engine test at the engine plants. You will not find these in any SERVICE balancer I have ever seen.

[David L.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

Joe,

I thought that the engines were internally balanced and that the balance plugs in my orig. 66 balancer were installed because the actual balancer was out of balance when it was made.

I know that my 94 Z28 w/LT1 engine is externally balanced and that if I change the balancer with a service balancer I have to put plugs in the service balancer exactly like the original balancer to keep everything on the engine in balance.

Dave

[Terry M.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

David,
The terms "internal balance" and "external balance" relate to whether the engine rotating assembly has enough mass to be balanced internal to the engine or needs mass added to the external components (generally the harmonic damper and/or flywheel/flex plate.

Examples of Chevrolet external balanced engines are 454 CID, and (I believe) 400 CID small blocks. An examination of the harmonic balancer and flex plate/flywheel used on 454 CID and 400 CID will show a large mass on these items to offset the lack of room inside the crankcase to attach this mass to the crankshaft. I would have to do some research to be sure, but I believe your Gen II LT1 is internally balanced.

The fact that there are balance weights added or removed from the harmonic balancer and/or flex plate/flywheel has nothing to do with whether the engine is internally or externally balanced.

Edit add: See link for a description:

http://www.eaglerod.com/index.php?option=com_content&task=view&id=27&Itemid=25

[Russ S.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

Enclosed are 4 photos of an original 1966 harmonic balancer (6 1/8" dia.) dated May 1966 (stamped "E 6 F" on the back side of the outer ring, photo #3). The "E 6" is the May 1966 date code and the letter "F" represents the manufacturer. The outer ring measures 3/4" in thickness where the front 1/2" machined surface measures 6.125" in diameter and the rear 1/4" cast surface measures 6.08" in diameter (see photo #2). This balancer was removed from a 1966 Chevrolet 327 engine (block casting # 3858180) stamped "T 0521 HAR" (May 21, 1966) on the front pad. I bought the entire engine back in the 1980's in a junk yard for $25 complete with carb., starter, flywheel, etc. where all the date codes matched up. Based on researching my many Chevrolet parts catalogs the GM part number for this balancer is 3883204 in Gr. 0.659. The 3883204 part number appears in only my 1966 Chevrolet Parts Catalog (effective Oct. 1965) and my 1966 Corvair-Chevy II-Chevelle Parts Catalog (effective Jan. 1966). The 3883204 balancer is a "one year deal" as it is not shown in my 1965 Chevrolet Parts Catalogs (Oct. 1964, Jan. 1965, and May 1965) and was discontinued in July 1966 according to Chevrolet Parts History and replaced with balancer # 3896903 (very similar in appearance, about 95%) which has been sold over the counter for many years.

Finally, here is my question.
Is there any owners of 1966 Corvettes w/300 HP engines that still have the original 6 1/8" diameter balancer balancer, and if so, is your balancer similar to the one that I have?

David, I have an original dated 6 C and it is exactly like yours with the exception of the plugs in the holes. RS

[David L.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

Russ,

Does your balancer also have the letter "F" after the "C 6" stamping?
I believe that there were 2 vendors that made these balancers, one used the letter "F" and the other used the letter "H".

My theory as why my original "E 6 F" balancer has the 2 plugs is that the outer ring on these 3883204 balancers were not 100% machined as indicated by the cast surface on the back 1/4" width and because of this balance plugs had to added as or if necessary. I may be right or I may be wrong. The 2 plugs in my balancer are each about 0.35" long.

Dave

[Russ S.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

Dave,There are no other letters on mine after the 6C. The stamp on mine is on the front side of the outer ring and the ring is machined completely on both sides. On the back side of the center casting are the numbers 388 and another 3 65 with a drilled and tapped hole between the 3 and the 65

[David L.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

Russ,

My 66 balancer also has the numbers ""388" and "3 threaded hole 5" on the back side of one of the cast spokes.

I also have the following balancers with the stampings on the FRONT face:

1969 balancer stamped "7704" and "B 9 F" (GM # 3947704 dated Feb. 1969)

1968 balancer stamped "4684" and "C 8 F" (GM # 3914684 dated March 1968)

1969 balancer stamped "7706" and "J 8 F" (GM # 3947706 dated Sept. 1968)

1971 balancer stamped "7701" and "1 S O" (GM # 3947701 dated ???), engine block stamped "K0217CGC" or Feb. 12, 1971

Dave

[Joe L.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

Joe,

I thought that the engines were internally balanced and that the balance plugs in my orig. 66 balancer were installed because the actual balancer was out of balance when it was made.

I know that my 94 Z28 w/LT1 engine is externally balanced and that if I change the balancer with a service balancer I have to put plugs in the service balancer exactly like the original balancer to keep everything on the engine in balance.

Dave

Dave-----

Balancers were balanced at the time of manufacture by the removal of material, as necessary, from the balancer ring. Also, I've never seen a SERVICE balancer with weights installed in any of the holes. If the weights were used to balance the balancer at the time of manufacture, I would expect that there would be just as much chance to find them in a SERVICE balancer as a PRODUCTION piece.

The 92-96 LT1 balancer situation you described illustrates this. As manufactured, the LT1 balancers are all identically balanced without the addition of any weights at the time of manufacture. Weights were added to the balancer ring holes as necessary at the time of final engine balance. So, if a balancer is replaced on an LT1 engine, the replacement balancer has to be weighted to mimic the original balancer.

[David L.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

Joe,

What you say does make sense. I also have never seen a service balancer with balance weights.

Back in 1966 do you have any idea how would they test the engine at the engine plants to know where to put the balance weights in the harmonic balancer?

Dave

[Joe L.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

Joe,

What you say does make sense. I also have never seen a service balancer with balance weights.

Back in 1966 do you have any idea how would they test the engine at the engine plants to know where to put the balance weights in the harmonic balancer?

Dave

Dave-----


I watched them do this in 1992 at the Flint V-8 engine plant. However, I do not recollect too much of it. Basically, they ran the engines for a short period at hot test. I very vaguely recall that somehow or another, something on the monitor informed the operator of the need to add balance weights and where to add them.

Of course, I don't know if the equipment used in 1966 was the same but it was likely similar in principle. There must have been something besides a computer monitor, though, because that had not been invented yet.

[Joe L.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

By the way, the balancer weights used to be a PRODUCTION-only piece. However, they later became a SERVICE-available piece after they were required for LT1/LT4 and LT5 engine SERVICE. The LT1/LT4 weight, used for both balancer and flywheel final balance is GM #274584. This is actually an ancient part number dating back to the 50's or prior. It's still available from GM.

The LT5 weight, used for both balancer and flywheel, is GM #3890192. This number dates back to later 1966 and it's also still available from GM.

[Timothy B.]

Re: Original 1966 (only) 300 HP balancer dated May 1966

I installed a 1966 dated 1021 flywheel on my 63 and there are holes around the perimiter for the balancing weights. When I took the pressure plate and flywheel to be balanced I removed the balance pins.

I don't believe this started until around 1965 because the 1963 flywheels and dampers don't have the holes around the ring.