LS6 flywheel

[Tom R.]

Can someone identify application of a flywheel with part number 3973457N, dated B150? It also has MODULAR GM cast in. It was on my 70 454 w/manual transmission. Preparing to reinstall and checked the number to find it's not original according to my parts book listing calling for 3993827. According to the dates on my heads of November 26 & December 4, 1969, is the casting date in February of 1970 for this flywheel just a coincidence assuming it's a replacement?

[Tom R.]

Re: LS6 flywheel

Before I get beat up - should have been LS5 flywheel.

[Joe L.]

Re: LS6 flywheel

Before I get beat up - should have been LS5 flywheel.

Tom------


I should hope so. All 1971 Corvettes with LS-6 used a special flywheel for use with the dual disc clutch which equipped all 1971 LS-6 with 4 speed. You don't want to need one of these flywheels.

However, the flywheel you have is the correct and original flywheel for your application. The number you see on the rear of the flywheel is a CASTING number and not a PART number for a finished piece. The original PART number for your flywheel was GM #3963535. The GM #3993837 part number you found in the P&A Catalog is a replacement part number which came into being in August, 1971 when the 3963535 was discontinued. However, I think that both flywheels use the same casting number.

Your flywheel was cast on February 15, 1970 and is very likely original to your car assuming that the engine was assembled sometime after that date.

[Tom P.]

Re: LS6 flywheel

In addition to the information provided by Joe, the casting number on the flywheel is for the flywheel itself, NOT for the complete assembly. Yes, that's right, flywheels are an assembly made up of two seperate parts: the flywheel and the starter ring gear. AFTER the flywheel is machined, then the starter ring gear is pressed onto the flywheel.
Now, here is a little extra information about manual tranny flywheels that many people are not aware of. Sometimes the starter ring gear teeth become excessively worn, or even chipped/broken. If this happens to a flywheel, one of two things can be done to save the flywheel. The ring gear can be replaced with a new one (I think new ring gears are only available aftermarket now), OR, the ring gear can be removed (gently tapped off with a heavy hammer and a soft drift) and flipped over so that the fresh side of the teeth can be engaged by the starter.
To re-install a ring gear that has been removed, the best way is to heat up the ring gear (I put it in the wife's oven at about 500deg for about 30min). Once heated up, I QUICKLY place it on the flywheel and gently tap it down until it is fully seated. This will give you another 30-50yrs of service from the same ring gear.

[Terry M.]

Re: LS6 flywheel

Now Corvettes are finally getting to the point that classic cars have been at for years.

I "rotated" the ring gear on the flywheel for my 1937 Cadillac back when my first Corvette was still a new car. I have demonstrated the process for my students numerious times. Real old school stuff.

BTW: Question for Joe: Doesn't the PRODUCTION flywheel assembly also include the pilot bearing?

[Paul D.]

Re: LS6 flywheel

Terry, Do you mean a pilot bearing would be shipped with a new flywheel? I never saw one included. The pilot bearing would be fitted in the crank. Chip.

[Terry M.]

Re: LS6 flywheel

Terry, Do you mean a pilot bearing would be shipped with a new flywheel? I never saw one included. The pilot bearing would be fitted in the crank. Chip.

Duh. Boy I blew that one. Right you are Paul.