Flywheel Number

[Brew14u]

I am changing the clutch on my 1969 Z28 with original 302 and Muncie m21.  In preparation for this, I bought a used flywheel a year ago and had it resurfaced to minimize the downtime for clutch replacement.  The number on the replacement flywheel is 379 021.  I just removed the existing flywheel, which shows 3791021.  They appear the same, bolt holes appear the same, and both have 153 teeth.  Are missing digits on cast components common?  Any reason to think the replacement flywheel is not compatible?  I hate working on my back laying under the car, so I only want to do this once.

[169INDY]

Well, to my mind would be, the Motor might have been balanced with the Existing Flywheel and now you are introducing a different flywheel that was NOT balanced with the rotating assembly, is this wise or acceptable?
I am not sure

Just throwing it out there for discussion purposes.

Guys?

[Brew14u]

Thanks for the response.  I thought that only the 400 cid small block engines were externally balanced.  Now that I have the existing flywheel out, although it is pretty scarred and burnt, I could have it turned. 

[rszmjt]

The picture of the lower flywheel appears to have 4 bigger holes in the back area, which is not stock GM balance IMO. Like mentioned the motor may have been balanced with the flywheel, so you could have a engine shop check the balance on both flywheels to see if they are close, but i doubt it.  I have seen shops do that instead of adding heavy metal to crank counterweights.

[GMAD_Van Nuys]

Brew14u - I believe you are correct that the Chevy 302 was internally balance and therefore the flywheel was neutrally balanced. 

[Brew14u]

The existing flywheel has many holes in the thick outer ring too.  I assume that this was done to balance it initially or at some point later.  I am not sure whether it is original, but it is dated E29 or May 2, 1969.  My engine is stamped 0605DZ, which seems possible.  The replacement is dated F258, so about a year older.

[Brew14u]

For future reference, it appears that the 379 021 and 3791021 flywheels are equivalent.  I went with the 379 021 flywheel and a LUK RepSet 04-021.  I finished getting it back together over the weekend and initial tests are good.  Starter engages well and engine is very smooth through out a range of rpms, but I may need to adjust the clutch linkage some more.

[Rossterman]

My 70 z28 flywheel says nodular on it. I’d expect they used the same on a 69 due to able to tolerate higher rpms better?