1963 Flywheel

[Joe L.]

Re: 1963 Flywheel

Yes, 3973456N. I weighed mine on a beam type as well. Thanks Joe.

Philip------


Somehow, I blew it when I weighed the flywheel. I re-weighed it. It weighs 29.1 lbs. I still cannot figure out how I made that mistake. Shameful.

A few other points: the flywheel I weighed is GM casting #789733 (I believe this is a contraction of the number 3789733). This is the flywheel, GM PART #3889694, that was was used 1966-69 Corvette big blocks (except L-88/ZL-1 and MA-6) and 1969 Corvette small blocks. My flywheel is dated "G259" (July 25, 1969) and is the original flywheel installed on my September, 1969 built small block.

GM CASTING #3973456N was GM PART #3973453 and was supposed to have been used for 1970 small blocks (except ZR-1) as well as 396 and 427 big blocks used in other Chevrolet models beginning in 1970. I am surprised to see it on a 1969 big block but it is possible it was used from late 1969. Does yours have a casting date on it?

The difference in the casting numbers between the flywheel I weighed and the one you have is likely what explains the slight difference in weight.

The final iteration of this flywheel was GM PART #3998281 but it was finally discontinued without supersession.

[Philip A.]

Re: 1963 Flywheel

Joe, no worries far from shameful. Thank you so much for re weighing it. Here is a pic of my flywheel and it looks like 1 28 9 is that correct? I dont see any letter followed by numbers like your "G259"
My car is a July car 22-23 or so. I have no idea or information to determine if this has been replaced over the years and is not the correct FW or it was resurfaced so many times that it now weighs 27.5
So, what do you think am correct in thinking that the GM flywheel should be 30 lbs for the 427?

[Joe L.]

Re: 1963 Flywheel

Joe, no worries far from shameful. Thank you so much for re weighing it. Here is a pic of my flywheel and it looks like 1 28 9 is that correct? I dont see any letter followed by numbers like your "G259"
My car is a July car 22-23 or so. I have no idea or information to determine if this has been replaced over the years and is not the correct FW or it was resurfaced so many times that it now weighs 27.5
So, what do you think am correct in thinking that the GM flywheel should be 30 lbs for the 427?

Philip------


I think the date is "I289" (an "I" was used on castings to represent the month of September). So, your flywheel casting date is September 28, 1969. It could only be original to your car if your car was built after that date. That date is also consistent with the casting number.

In addition, as I mentioned the 3973456 casting is generally considered to be a 1970 model year and later usage. Most 1970 Chevrolet models except Corvette and Camaro were already in PRODUCTION by September, 1969. But, many 1970 model year mechanical parts (e.g. flywheels) were used on very late 1969 Corvettes.

As far as weight goes, it is possible that your flywheel has been re-surfaced and that could account for the difference in weight from my flywheel. However, as I mentioned, the difference could also be just the result of the difference in the casting numbers----different numbers, different casting configurations. However, I am 100% certain that my flywheel has never been surfaced. So, it's weight of 29.1 lbs should be pretty close to its as-new weight except for a likely negligible loss due to wear.

How do I know that my flywheel has never been resurfaced? Well, I have owned my 1969 since new. This flywheel was used for most of its life although I did replace the clutch twice. In addition, I NEVER USE resurfaced flywheels. If a flywheel needs to be re-surfaced, I discard it and use a new one.

[Philip A.]

Re: 1963 Flywheel

Ahh that makes sense as to why the number I thought was 1 is slanted. It's an I. Unfortunately pretty safe to say this FW didn't come on my car with it being a July car. Oh well replacing it anyway but I'll keep it and see if someone needs that to match their cars date
Thanks Joe and congrats on owning your 69 since new!

[Gary B.]

Re: 1963 Flywheel

Philip------


Somehow, I blew it when I weighed the flywheel. I re-weighed it. It weighs 29.1 lbs. I still cannot figure out how I made that mistake. Shameful.

A few other points: the flywheel I weighed is GM casting #789733 (I believe this is a contraction of the number 3789733). This is the flywheel, GM PART #3889694, that was was used 1966-69 Corvette big blocks (except L-88/ZL-1 and MA-6) and 1969 Corvette small blocks. My flywheel is dated "G259" (July 25, 1969) and is the original flywheel installed on my September, 1969 built small block.

GM CASTING #3973456N was GM PART #3973453 and was supposed to have been used for 1970 small blocks (except ZR-1) as well as 396 and 427 big blocks used in other Chevrolet models beginning in 1970. I am surprised to see it on a 1969 big block but it is possible it was used from late 1969. Does yours have a casting date on it?

The difference in the casting numbers between the flywheel I weighed and the one you have is likely what explains the slight difference in weight.

The final iteration of this flywheel was GM PART #3998281 but it was finally discontinued without supersession.

[Harry S.]

Re: 1963 Flywheel

Joe,

So, If I was looking for a 153 tooth flywheel for my 1963, 300 hp car what is my best choice from GM? If nothing is available from GM, what is my second best choice.

Thank you

[Joe L.]

Re: 1963 Flywheel

Joe,

So, If I was looking for a 153 tooth flywheel for my 1963, 300 hp car what is my best choice from GM? If nothing is available from GM, what is my second best choice.

Thank you

Harry------

The last available flywheel from GM that would work for your application was GM #14085720 although this was a lightweight flywheel and not a direct replacement for the original standard weight flywheel. The original flywheel was discontinued a very long time ago. The 14085720 is now also discontinued.

My choice for a replacement would be a ductile iron Perfection #506516. However, I believe this is a 15 lb flywheel.

[Harry S.]

Re: 1963 Flywheel

Joe, thank you

[Gary B.]

Re: 1963 Flywheel

Harry------

The last available flywheel from GM that would work for your application was GM #14085720 although this was a lightweight flywheel and not a direct replacement for the original standard weight flywheel. The original flywheel was discontinued a very long time ago. The 14085720 is now also discontinued.

My choice for a replacement would be a ductile iron Perfection #506516. However, I believe this is a 15 lb flywheel.

All,

Summit Racing sells that flywheel for $102 and the description says it weighs 16 lbs. So, definitely in the lightweight category.

GM-discontinued flywheels occasionally show up on eBay as NOS examples. I bought an NOS GM #3791022 in 2019 on eBay for what I felt was a reasonable price (2x the cost of the 506516 Summit flywheel). I preferred a GM NOS flywheel that was the same weight as the original on my ‘66.

Gary