Bbc 9/16-18 Harmonic Balancer bolt

yevgenievich · Apr 19, 2022

Looking to see if anybody ran in to the 9/16 balancer bolt used on approximately 2007-2016 bbc? Did not check with a dealer yet as last time I called regarding push rods for this thing, they did not have a clue. Ford and Chrysler used 9/16 on some motors that I might try(they are a bit long), but thought of posting here.

Or just use a grade 8 bolt and call it good?

Schurkey · Apr 19, 2022

All I see is 1/2-20.

Hell, I didn't know GM put big-blocks in anything post-8.1L; I thought the "big-block" was DONE after...2007.

yevgenievich · May 4, 2022

I think this will end up just being a grade 8 bolt with a shoulder type thing.

MrPink · May 4, 2022

Schurkey said:
All I see is 1/2-20.

Hell, I didn't know GM put big-blocks in anything post-8.1L; I thought the "big-block" was DONE after...2007.

in performance applications it is still avail. but as far as from the factory, the 8.1L replaced the 7.4L. there may be an obscure medium duty truck that has the 454 in it from 07-16 but the "BBC" was "dead" with the GMT400 and any med duty chassis in 2001/02.

quoted from wiki

Vortec 7400 (L21)[edit]

The Vortec 7400 L21 was a commercial version of the Chevrolet Big-Block engine used in the medium duty truck platform. Its design shared much with the L29 454, but with the addition of forged pistons and crankshaft, and coil near plug ignition. It had slightly reduced power compared to the L29 454 and used a different PCM. The L21 was paired with the early 4 speed Allison automatic transmission or manual transmission, depending on the application.

L21 Applications:

1998–2001 Chevrolet Kodiak/GMC TopKick/Isuzu H-Series 4500 5500
1998–2001 Kodiak/Topkick
1998–2001 P12 HD Motorhome Chassis. The Workhorse W-20 is a clone of the P12 Chassis.

yevgenievich · May 4, 2022

8.0l replaced 7.4l for industrial use up until around 2016

MrPink · May 4, 2022

so which do you need the bolt for the 8.1L or a 7.4L?

Papablunt · May 4, 2022

Eh, just throw a grade 8 in there and move on. Nothing special about that bolt other than the duty it performs.

I had to retap my crank to the next size up, and I just threw in a grade 8 bolt.

MrPink · May 4, 2022

The 8.1L in 06 used a M16x1.5, the 7.4L in 99 used a 1/2-20 bolt.

yevgenievich · May 4, 2022

MrPink said:
so which do you need the bolt for the 8.1L or a 7.4L?

it is 8.0l, not 8.1l
8.0l used standard bolts. Basically mostly everything as in 7.4l except larger crank bolt. But also pistons, rods and cam from 8.1l

Schurkey · May 4, 2022

Go to the GM dealer?

Bbc 9/16-18 Harmonic Balancer bolt

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Vortec 7400 (L21)[edit]