Seeking Advice and Program Details for Crankshaft Balancing on 1978 Ferrari 308 2 Valve Engine | FerrariChat
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Seeking Advice and Program Details for Crankshaft Balancing on 1978 Ferrari 308 2 Valve Engine

Discussion in '308/328' started by ItalianProjects101, Apr 18, 2024.

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  1. ItalianProjects101

    ItalianProjects101 Karting

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    #1 ItalianProjects101, Apr 18, 2024
    Hey everyone,

    I'm currently in the process of rebuilding my 1978 Ferrari 308 2 Valve engine. After much recommendation here I will be swapping out the stock pistons for aftermarket Wossner pistons. With this upgrade, I understand the importance of balancing the rotating assembly, including the crankshaft, rods, pistons, flywheel, and pulley, to ensure optimal performance and longevity.

    However, my machine shop doesn't seem to have the necessary program for crankshaft balancing using bob-weights for this particular engine. They're reaching out to their network, but I wanted to reach out to the knowledgeable community here on Ferrari Chat to expedite the process.

    If anyone has experience with this specific engine and could share advice or details on the program needed for crankshaft balancing by bob-weights, I would greatly appreciate it.

    Thank you in advance for any assistance you can provide!
     
  2. Newman

    Newman F1 World Champ
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    #2 Newman, Apr 18, 2024
    You don't have to use bob weights on a flat plane crank but they should weight-match the reciprocating parts.
     
  3. ItalianProjects101

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    #3 ItalianProjects101, Apr 18, 2024
    They already are nearly fully balanced, only a gram or two off between pistons
     
  4. waymar

    waymar Formula 3

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    #4 waymar, Apr 18, 2024
    As those before me stated…… All of the parts are balanced to themselves as sets…..ie: crank is balanced to itself, Pistons, rods, flywheel, etc are balanced as sets. Swapping parts out as sets is no problem. So if your new pistons are lighter or heavier by 30 g it does not matter as long as all of the Pistons are matched to themselves.
     
  5. ItalianProjects101

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    #5 ItalianProjects101, Apr 18, 2024
    Old Pistons with gudgeon pin, clips and rings are 449grams
    New Pistons with gudgeon pin, clips and rings are 414grams
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    The new pistons when weighted independently range from the lightest being 321 grams and the heaviest being 324 grams. So from what I am understanding is that I should remove material from the heavier ones, the other pistons are all around 322, should I match the weight of opposing cylinders?

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  6. Dockboy

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    #6 Dockboy, Apr 18, 2024
    You have to weigh the rods also. If the rods have a 1-3 gram difference also, use the heavier rods on the lighter pistons. As stated above, you want all 8 of the piston/rod assembly's to weigh the same.
     
  7. ItalianProjects101

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    #7 ItalianProjects101, Apr 18, 2024
    So practically whats important is that the components of the opposing cylinders weight the same correct?

    I’m asking this because the the rods are already numbered by factory as to which cylinder they should go in
     
  8. Dockboy

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    #8 Dockboy, Apr 18, 2024
    Are you using a Machine Shop or doing this yourself?

    If using a Machine Shop, just drop off your rods, pistons, pins, etc. and have them balance all the assemblies.

    If not, and you don't have a rod scale to weigh the big and small ends of the rod, weigh the overall rod and put the heaviest piston on the lightest rod and so on.

    If you can get the assemblies within a gram or two of each other you would be fine. If the difference is more than 4 or 5 grams, you need to take them to a shop that has the equipment and scales to balance them.
     
  9. ItalianProjects101

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    #9 ItalianProjects101, Apr 18, 2024
    I was gonna drop them off to a machine shop, but shouldn't the rods be kept in the same place as they are numbered?
     
  10. Dockboy

    Dockboy Formula Junior
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    #10 Dockboy, Apr 18, 2024
    Ideally. If you are dropping them off to a shop, they should come back to you balanced with the piston and rod already assembled. Then put #1 in the #1 hole and so on.
     
  11. Newman

    Newman F1 World Champ
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    #11 Newman, Apr 18, 2024
    Does anyone notice a very critical detail on the new pistons that is missing and can cause a disaster?
     
  12. ItalianProjects101

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    #12 ItalianProjects101, Apr 18, 2024
    what are you referring to exactly?
     
  13. bitsobrits

    bitsobrits Formula Junior
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    #13 bitsobrits, Apr 18, 2024
    The cut out at the piston edge for the intake valve?
     
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  14. Newman

    Newman F1 World Champ
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    #14 Newman, Apr 18, 2024
    Correct but if the engine is being assembled properly then a valve to piston clearance check including radial clearances will be performed. That notch is there for a very good reason on the factory piston.
     
  15. ItalianProjects101

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    #15 ItalianProjects101, Apr 18, 2024
    It will and is going to be assembled with the help Of a professional having said that I am also reading to make sure its done correctly

    so my question is what notch are you referring to exactly?
     
  16. Rifledriver

    Rifledriver Three Time F1 World Champ

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    #16 Rifledriver, Apr 18, 2024
    Wossner makes very good pistons and am willing to bet the valve reliefs are much bigger than needed unless you are using some custom cams. Wossner is the supplier for GTO Engineering for their replacement engines. They have been making high quality pistons for 2 valve Ferrari engines for some time. Their high compression pistons work great in 308 street engines. I wish they would supply pistons for 4 valve engines.
     
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  17. ItalianProjects101

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    #17 ItalianProjects101, Apr 18, 2024
    I’ll be using catcams street cams so quite mild nothing out of the ordinary somewhat similar to stock eu cams either way we’ll be checking valve clearances to make sure everything works correctly
     

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