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blown 540 vibration

  1. #1
    Senior Member Smallblocksperry's Avatar
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    Default blown 540 vibration

    so i finally finished my motor and got it running, boat runs great minus one issue. It has a weird vibration and im not sure if its just due to that big mountain motor in such a light layed up boat or if i have a motor that wasnt balanced properly???

    its smooth as silk at idle, but in neutral when you rev it, itll throw a vibration throughout the boat, when driving it in between idling and putting a load on it it has that same vibration, once you plane it out and start opening her wings its smooth.

    when i got back from the lake yesterday i pulled the bravo drive off and checked the gimble bearing and the alighment, everything checked out fine, fired the boat up with the drive off and the vibration is still there, its pretty minor i could just be being overcautious, but my buddy also noticed it.


    the engine is a nautral balanced motor, dampner has no weights on it, etc.

    the short block was balanced back east without the flywheel or balancer, figured that would be fine due to the engine being neutral balance.

    anyone got any ideas for what to check?
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    Senior Member SHAWN DAVIS's Avatar
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    Make sure you dont have a weighted balancer-flywheel, other than that you have a rotating balance issue.
    I put a couple engines in ones similar to yours, 26 american offshores, never any noticable vibrations, especially with the drive off.
    Most vibrations seems to come from the props

  4. #3
    Senior Member Smallblocksperry's Avatar
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    Quote Originally Posted by SHAWN DAVIS View Post
    Make sure you dont have a weighted balancer-flywheel, other than that you have a rotating balance issue.
    I put a couple engines in ones similar to yours, 26 american offshores, never any noticable vibrations, especially with the drive off.
    Most vibrations seems to come from the props

    the balancer definately doesnt have a weight on it, 7" supercharger balancer

    the flywheel im not positive on, it was on the gen 6 502 motor that came out of the boat, didnt notice any weights on it, do they have weighted and non weighted flywheels, standard mercruiser bravo deal im pretty sure

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    Senior Member TNYoungblood's Avatar
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    Check ur flywheel
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  7. #5
    gn7
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    Quote Originally Posted by Smallblocksperry View Post
    the balancer definately doesnt have a weight on it, 7" supercharger balancer

    the flywheel im not positive on, it was on the gen 6 502 motor that came out of the boat, didnt notice any weights on it, do they have weighted and non weighted flywheels, standard mercruiser bravo deal im pretty sure
    All Gen 5-6 flywheels/flexplates are counter balanced.



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    Quote Originally Posted by Smallblocksperry View Post

    the flywheel im not positive on, it was on the gen 6 502 motor that came out of the boat, didnt notice any weights on it, do they have weighted and non weighted flywheels, standard mercruiser bravo deal im pretty sure
    Quote Originally Posted by gn7 View Post
    All Gen 5-6 flywheels/flexplates are counter balanced.
    Yep, the GM 502's are externally balanced. While it is possible to either drill or machine the counterweight, I am thinking that may not match the quality of the rest of your engine and boat.

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    gn7
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    Quote Originally Posted by obnoxious001 View Post
    Yep, the GM 502's are externally balanced. While it is possible to either drill or machine the counterweight, I am thinking that may not match the quality of the rest of your engine and boat.
    And the Gen 454s and the 8.1s

    Although I doubt it will see RPM higher than the wheel can handle when in front of a Bravo, I think I ditch the stock wheel too. Failed wheels are never pretty.



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  10. #8
    Senior Member Smallblocksperry's Avatar
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    after talking with Alexi from boostpower we came to the conclusion that i am F**ked once again on my project, i need a zero balance flywheel, and that damn 502 flywheel like everyone stated above is not zero balanced, so once again i have to pull the motor, haha FML


    oh well at least i didnt run it enough to hurt it, another lessons learned scenario..... next time im sending everything that attachs to that damn crankshaft when the motor goes out for balancing, neutral balance or not.

  11. #9
    Some guy obnoxious001's Avatar
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    Quote Originally Posted by Smallblocksperry View Post
    next time im sending everything that attachs to that damn crankshaft when the motor goes out for balancing, neutral balance or not.
    That is the correct way to do it. Many times even internally balanced parts will need a small correction.

    The other thing is that many times when "balanced assemblies" are sold, they might not actually balance each piston and rod, instead just batching them together, within a gram or so. I have lots of confidence in the guy I use, have known him close to 35 years I think now.

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    Official Test Driver BOOSTPOWER's Avatar
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    How is that deal runnin?


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  13. #11
    Senior Member Smallblocksperry's Avatar
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    Quote Originally Posted by BOOSTPOWER View Post
    How is that deal runnin?


    Sent from My BOOSTPOWER Efi Beacon
    ran good for about 12 hours before i lost the timing set. i used a jegs brand billet timing set that i had in the garage (it was brand new so i figured with a .650" lift solid roller it would be fine) well the chain let go and wacked all of my intake valves on the pistons. took a little break for the winter and about to jump back on it to go and run it at dezert storm. adding methanol injection and doing some transom repairs before i put the motor back in.
    thanks for the help in getting my vibration problem worked out, now that the motors tore down i'm going to have the rotating assembly balanced together

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    Quote Originally Posted by Smallblocksperry View Post
    ran good for about 12 hours before i lost the timing set. i used a jegs brand billet timing set that i had in the garage (it was brand new so i figured with a .650" lift solid roller it would be fine) well the chain let go and wacked all of my intake valves on the pistons. took a little break for the winter and about to jump back on it to go and run it at dezert storm. adding methanol injection and doing some transom repairs before i put the motor back in.
    thanks for the help in getting my vibration problem worked out, now that the motors tore down i'm going to have the rotating assembly balanced together
    Bummer! Perhaps a gear drive for you this time. We use comp billet chains but the setup needs to be just right. Thanks for the reply.


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  15. #13
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    Quote Originally Posted by Smallblocksperry View Post
    ran good for about 12 hours before i lost the timing set. i used a jegs brand billet timing set that i had in the garage (it was brand new so i figured with a .650" lift solid roller it would be fine) well the chain let go and wacked all of my intake valves on the pistons. took a little break for the winter and about to jump back on it to go and run it at dezert storm. adding methanol injection and doing some transom repairs before i put the motor back in.
    thanks for the help in getting my vibration problem worked out, now that the motors tore down i'm going to have the rotating assembly balanced together
    This is why I use nothing but Rollmaster on my builds. Best timing set on the market, hands down.
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  16. #14
    gn7
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    Think running/driving that thing with a out of balance with the wrong flywheel didn't play a hand in the short life if that chain?



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