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Technical lightening a flathead flywheel

Discussion in 'Traditional Hot Rods' started by FlatJan, Mar 31, 2021.

  1. FlatJan
    Joined: Dec 13, 2013
    Posts: 259

    FlatJan

    Hi
    i m thinking of lightning my flathead flywheel.
    now i asked myself how it would affect balancing.
    the motor i want to modify is correctly balanced.

    are crankshaft and flywheel balanced together or is this done separately/ individually?
    so if i take some 12..16 pounds out of the backside of the flywheel by turning on a lathe, from my understanding, it should keep its balance, as i take out material in a circular manner
    but will the complete motor/crankshaft-flywheel-assembly still be ok and correctly balanced?
    thank you guys
    Jan
     
    Last edited: Mar 31, 2021
  2. alchemy
    Joined: Sep 27, 2002
    Posts: 16,727

    alchemy
    ALLIANCE MEMBER

    Flathead cranks should be balanced separately from the flywheel. If you remove material from your flywheel it would be a consistent cut from all around, but somehow it might still cause imbalance. It should probably be rebalanced. If you want to get really exact, install the pressure plate on the flywheel, mark them permanently, and balance those two together.
     
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  3. dana barlow
    Joined: May 30, 2006
    Posts: 4,310

    dana barlow
    Member
    from Miami Fla.
    1. Y-blocks

    Too check,put the flywheel by it's self on a wheel balancer>to see if it is in balance?.
    If it is ,then cut as much WT. off as you wish ,with out over doing it*.< don't get thin in center. Then check balance again same way,an fix as needed. Remember,you need more fly wheel WT. too work well>,the more the car curb weight is*.
    Dose not need to be super fanzy. Even one of these can make a check n work. But better is better!
    [​IMG]
     
    Last edited: Mar 31, 2021
    FlatJan likes this.
  4. Tman
    Joined: Mar 2, 2001
    Posts: 33,857

    Tman
    ALLIANCE MEMBER

    @mctim64 has experience with this. He has posted some pics in the past.
     

  5. FlatJan
    Joined: Dec 13, 2013
    Posts: 259

    FlatJan

    hey guys
    thanks for the quick info!
    @dana barlow wheel balancer is a great idea :D
     
    dana barlow likes this.
  6. Weedburner
    Joined: Nov 16, 2010
    Posts: 200

    Weedburner
    Member
    from Wa State

    If you are lightening your own flywheels, you might also want to make a fixture to balance it yourself. No need for dynamic balancing a simple flywheel, as there's not many choices as to where to remove weight.

    I made this simple balance checking fixture a while back, wanted something to quickly verify flywheel and PP balance at home. Turned out it works pretty good for what it is, detects an an out of balance 1 gram on a 6" radius. Here's some pics with an old cast flywheel i had laying around, here you can see some leveling screws installed in the base...

    [​IMG]

    Here you can see that one end of the support shafts non-adjustable, just holes for the pins that are threaded into the shafts...

    [​IMG]

    Here you see the other end of the support shafts, which go into slotted holes with adjustment screws to allow adjustment for parallel of the support shafts...

    [​IMG]

    Here you can see that the old flywheel, supposedly neutral balanced originally, required 43 grams applied to it's rim to achieve neutral balance...

    [​IMG]

    I static balanced a steel flywheel i'd been using on my 355, forgot to write down exactly how much weight it took before I started drilling. I had taken a little weight out of the backside a year or so ago, i'm guessing it took about 12g to balance it out today.

    With the flywheel zero'd out, I bolted the Ram pressure plate on to check it's balance. Turns out it needed 22g. I then rotated the PP 180 degrees on the flywheel and checked it again to verify. Took the same 22g on a 5-1/8" radius in the same "6" location.

    Looks like depending on how the two were bolted up before, balance of this assembly could have been out a minimum of 10g or a maximum of 34g overall...

    [​IMG]

    I ended up replacing the cover bolt in the #6 location with a longer double ended stud with a shoulder, and made a weight to fit over the stud. Ram says they balance to .5 ounce inch, that's around 2.5 grams at the bolt circle radius.

    Also found that if I need to set up the fixture on the concrete floor instead of the bench plate to get 1g @ 6" resolution. My 65lb bench plate in the above pics plugs into a single 2" square receiver style socket in the bench, turns out there was a little flex when the parts were rolled from one side of the plate to the other...

    [​IMG]

    The above used dual friction disc was only out 1g @ ~ 5".

    Grant
     
  7. Marty Strode
    Joined: Apr 28, 2011
    Posts: 5,690

    Marty Strode
    Member

    Taking 12 lbs off a flathead flywheel is a risky endeavor, in my opinion. I recently removed 5 lbs off one for a 59 engine, it weighed 34 lbs at the start. Not sure what you are working with, but taking 12 off the one I did, would reduce the total weight by more than 1/3. Mine only measured .700 thick in the area I machined. I have seen the destruction caused by exploding cast iron flywheels, so for safety sake, tread lightly. Here are a couple of examples, of the machine work. Good luck. IMG_6574.JPG IMG_6576.JPG IMG_0334.JPG IMG_0335.JPG
     
  8. rusty valley
    Joined: Oct 25, 2014
    Posts: 2,443

    rusty valley
    Member

    I used an early flywheel with the big blob around the outside, and 9" clutch. I cut the blob off in my lathe, had it surfaced and balanced. The result was a quick reving motor, but my mild motor, 59a, 4" crank, merc cam,single carb, could slip the clutch goin down the highway. need heavier springs, or a 10" clutch
     
  9. solidaxle
    Joined: Jan 6, 2011
    Posts: 533

    solidaxle
    Member
    from Upstate,NY

    If no one does it in your neck of the woods to save on the shipping cost. Send it to Al at Go Devil Garage in Schodack, NY. He removed 7lbs off mine. To tell you the truth, there is no seat of the pants difference. The other option is to purchase aluminum one with an insert.
     
  10. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,848

    ekimneirbo
    Member
    from Brooks Ky

    How much does the flywheel weigh now? Where do you plan to remove the weight from? If all the weight is removed from the face, it should not be a problem, just leave a little so you can get it ground after turning. For the most part, a flathead isn't going to be reved enough to create a problem. I don't really believe that removing weight is going to help much, and you may find the engine doesn't idle as smoothly. It just depends on what you want from the engine when done.
     
  11. krylon32
    Joined: Jan 29, 2006
    Posts: 7,206

    krylon32
    Alliance Vendor
    from Nebraska

    Are the new machined billet flywheels offered by some manufacturers close to zero or do they require some balancing? I see them on E-bay and have had a few customers buy them with no feedback.
     
  12. FlatJan
    Joined: Dec 13, 2013
    Posts: 259

    FlatJan

    hey Guys
    just checked in again and man there's more great info :) thanks to all of you!
    would not have expected that in such a short time.
    your are right i was a little high with the wanted weight reduction. i will go easy when starting to turn it down. right now i have an 11" clutch ( original French Flathead) for a 28 AV8 roadster, so all kinda heavy for the car. maybe I'll start by taking out 2..4 pounds, balance and check if there is a noticeable change in the revving..and then maybe the next step..
    maybe also in a later step i should redrill the flywheel , change to a 9" clutch and turn down the unnecessary part for the then replaced 11" clutch.
    this is what was recommended to me and makes a lot of sense to me
     
  13. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,848

    ekimneirbo
    Member
    from Brooks Ky

    Quite honestly, I don't think you will see any noticeable difference. Lightening flywheels usually only offers a benefit on high reving engines..........which flatheads aren't. A heavy flywheel helps a lower powered car take off because the enertia of the heavier mass keeps the lower powered engine spinning instead of bogging against a load when taking off. With a more powerful high reving engine, a higher rpm is employed when taking off, and then the engine revs faster with the lighter flywheel. With an engine that doesn't rev high, there is little to gain from lightening, and then takeoff often suffers.;)
     
  14. J'st Wandering
    Joined: Jan 28, 2004
    Posts: 1,772

    J'st Wandering
    Member

    I have a flathead with stock flywheel and one with an aluminum flywheel. For me, there is a big difference. The lighter flywheel allows the rpm to increase and drop much faster. Makes it nicer for shifting and acceleration.
     
    rusty valley likes this.
  15. rusty valley
    Joined: Oct 25, 2014
    Posts: 2,443

    rusty valley
    Member

    I agree, it seems to make a big difference here too. A light car doesnt need the inertia to get started. The throttle is very responsive. Late great rumble seat used to say the early flywheel with the blob cut off and a 9" is the lightest "ford" set up, so thats what i did. However Iguess I missed the part about using stronger springs in the PP so, mine will slip and has to come apart again
     
  16. solidaxle
    Joined: Jan 6, 2011
    Posts: 533

    solidaxle
    Member
    from Upstate,NY

    Seems like your making a lot of work for yourself. I would change the clutch out to 9inch. Here's Rumble Seats take on it.
     

    Attached Files:

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  17. rusty valley
    Joined: Oct 25, 2014
    Posts: 2,443

    rusty valley
    Member

    Thanks @Solidaxel for the refreshing read. I need to do something about my slippage problem, but do not like the idea of greater pedal pressure from heavier springs. not sure what way to go next
     
  18. 19Fordy
    Joined: May 17, 2003
    Posts: 7,117

    19Fordy
    Member

    Weedburner, Your balancing set up is really a neat idea and very well made. Maybe you could set up a side business of balacning flywheels.




     
  19. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,750

    V8 Bob
    ALLIANCE MEMBER

    I'm using a SFI Centerforce steel flywheel that required no re-balance, and weighs about 26 lbs compared to the stock 8BA wheel of about 35 lbs. These are drilled for Long and diaphragm/B&B pressure plates.
     
    Last edited: Apr 1, 2021
    rusty valley and KiWinUS like this.

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