1. Welcome to PlowSite. Notice a fresh look and new features? It’s now easier to share photos and videos, find popular topics fast, and enjoy expanded user profiles. If you have any questions, click HELP at the top or bottom of any page, or send an email to help@plowsite.com. We welcome your feedback.

    Dismiss Notice

Balanced Flywheel and Intake manifold question

Discussion in 'Chevy Trucks' started by steven1213, Mar 10, 2008.

  1. steven1213

    steven1213 Junior Member
    Messages: 20

    I am installing a 350 motor (1981 year) and the flywheel was cracked. He said I could not use the flywheel from my 400 engine because it was balanced.The flywheel i got from the auto parts store has a weight on the back of it. Did they give me the wrong flexplate?
    Also I was wondering if it is recommended that silicone in addition to the gasket when installing the intake manifold.--Thanks for any help----Steve
  2. Earthscapes

    Earthscapes Senior Member
    from WNY
    Messages: 577

    All 350 flywheels have a weight on them. Usually 2-4" long.
    I never use the 2 rubber gaskets that come in the kit. Put a couple small dabs of RTV black to hold the side gaskets in place, then put a heavy bead of RTV Black along the block, front and rear. Let it setup for about 5 mins, and carefully place the intake on. Bolt it down right away and do not remove the excess RTV. Finish bolting everything else on, but try to let it setup over night before running it.

    If your in a pinch you can dry the RTV with a propane torch, as I have done many, many times at the racetrack..........

  3. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Only ALL '86-up 350's with the one piece rear main seal have the long balance weight on them.

    '85 and prior 350 (or 305) should not have a large weight. They may have a very small one or have balancing holes drilled through the flex plate, but shouldn't have the large weight. Only 400 or 454 use the large weight ('85-prior)
  4. Earthscapes

    Earthscapes Senior Member
    from WNY
    Messages: 577

    I stand corrected the largest block is 1-1/2" and the holes are there. I just finally got off my butt and walked into the garage and measured all 9 of them. Our blocks are all pre 85'. Sorry.......
  5. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    This is correct. And the '86+ plates won't fit due to a different bolt pattern on the one-piece seal crank.
  6. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    One other little tidbit of info while were talking flywheel/flex plate weights...

    Many guys think the 400 and 454 use the same weighted flywheel since they look the same and of course the bolt pattern is the same, but in actuality the balance weights don't quite weight the same (slightly different lengths) and they're also in slightly different locations. If you have them side by side you can see the difference but individually it's hard to tell without an experienced eye.