Flywheel change = rebalancing? | FerrariChat

Flywheel change = rebalancing?

Discussion in '206/246' started by Alex_202, Sep 30, 2009.

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  1. Alex_202

    Alex_202 Karting

    Apr 10, 2008
    66
    Sweden
    I'm looking at changing the flywheel on my 246 engine from the standard to a lightened steel wheel. Assuming the flywheel is perfectly balances, will I have to take the engine apart and rebalance the crankshaft and new flywheel?
     
  2. TonyL

    TonyL F1 Rookie

    Sep 27, 2007
    3,811
    Norfolk - UK
    Full Name:
    Tony
    It would be better to explain why you want to fit a lightened flywheel?

    The problem is balancing or blueprinting involves the whole mass from torsional damper to flywheel /clutch, changing any components could and IMO will affect the balance.

    Rebuilding the whole thing seems extreme, but remember any variation in weight of individual items increases with speed squared.

    So any force created by the imbalance from the axis (centre of crank) will increase with speed. So a 4 gram (1 sheet of A4 paper) imbalnce @ 2,000 rpm will be subjected to a force of 6kg . At 3,500 rpm, the force grows to approx 26kgs.! Double the speed again to 7,000 rpm and the force is over 91kgs (200lbs)

    Tony
     
  3. Alex_202

    Alex_202 Karting

    Apr 10, 2008
    66
    Sweden
    I'm using this engine as a temporary solution in my replica of a 1960 Ferrari 246 F1. In short, the rotating mass that the fly wheel provides in a normal setup, is in this car provided by the rotating parts of the gearbox. The only reason I need the flywheel is to be able to use a starter.

    This is the reason why I want to mount a fly wheel that is as light as possible.
     
  4. sowest

    sowest Formula Junior

    Aug 18, 2006
    899
    Hi

    I am uncertain what engine you are using in your car. If you are putting in an engine from a normal 246 GT/GTS road car, the flywheel and front damper pulley are integral to the balance of the rotating mass. The normal 246 road car crankshaft is externally balanced, which means that it needs the offset weights that are built into the flywheel and front damper pulley to make the whole assembly balanced. If you replaced the stock flywheel with a light aluminum unit without the offset weight, you would get a very distinct vibration.

    If the crankshaft that you are using is from a real race engine and is internally balanced, then all you would need to do is make sure that the new flywheel is balanced as the crankshaft does not depend on the flywheel to make it "whole".
     
  5. Alex_202

    Alex_202 Karting

    Apr 10, 2008
    66
    Sweden
    I will be using a standard 246 GTS engine. This car has the engine in front and a rearmounted transaxle gearbox with an internal clutch. The thing is that the driveshaft and main shaft of the gearbox will rotate when the engine is running and car stationary, ie providing a rotating mass that wouldn't have to be on the flywheel.

    How do I get this engine balanced - can it be acheived with the existing damper?
     
  6. sowest

    sowest Formula Junior

    Aug 18, 2006
    899
    Hi

    I wish that I had a 246 flywheel here to look at (and take a picture of). If you can look at the side of the flywheel that is opposite of the clutch surface, you should see that there is an offset weight that is part of the casting. The crankshaft is not fully counterweighted by itself and needs this additional, external weight to complete the balance. This is true at both ends of the shaft. The damper provides the weight at the front and the flywheel provides the weight at the rear.

    I now understand what you are trying to do and what the problem is. If you wanted to have a very light unit on the engine that is primarily a support for the ring gear, it would have to include an offset weight. I don't know if a good crankshaft shop could match the amount of offset weight by working with the flywheel alone. If it was possible, it would save the time and trouble of disassembling the engine so that the crank, damper, and flywheel could be balanced as a unit.

    I don't know enough about the theory here to know if the crankshaft could be modified so that it is "internally" balanced and eliminate the need for the external, offset weights. It might be worth talking to a real expert on the subject.

    It should be possible because the 206 Dino has solved the issue that you are up against. The Fiat 206 Dino crankshaft is "externally" balanced. The Ferrari 206 Dino crankshaft is "Internally" balanced. IF you would be satisfied with a 206 and IF you could find a Ferrari 206, your problem would be solved.

    I hope this was helpful and not just confusing!
     
  7. Alex_202

    Alex_202 Karting

    Apr 10, 2008
    66
    Sweden
    The thing is that I already have two Ferrari 246 engines and am reluctant to go on a chase for a third engine :-D

    If I've understood this correctly, the 246 is externally balanced by the damper at the "front" and flywheel at the "rear". The mass of the flywheel has nothing to do with balance of the engine but has to be weighed in a way that it together with the damper is balanced. Hence, if I change the flywheel, the new has to have the same "imbalance" as the old in order not to have to tear the entire engine apart.

    Is this correct?
     
  8. sowest

    sowest Formula Junior

    Aug 18, 2006
    899
    Yes! You are correct and have stated the problem/solution very well. I could see making up a ring gear assembly with a reduced overall mass, but it would still have to have an eccentric weight differential that is equal to the original flywheel. I think a good balance shop that could appreciate a bit of a challenge could do this for you.

    By the way, your command of English remarkable. Also, I for one, would be very interested in seeing some pictures of your project.

    Aloha
    Larry
     
  9. swift53

    swift53 F1 Veteran
    Rossa Subscribed

    Nov 17, 2007
    6,676
    E.S.
    Full Name:
    Alberto
    #9 swift53, Oct 2, 2009
    Last edited by a moderator: Sep 7, 2017
  10. Alex_202

    Alex_202 Karting

    Apr 10, 2008
    66
    Sweden
    #10 Alex_202, Oct 2, 2009
    Last edited by a moderator: Sep 7, 2017
    Here's a picture of the status a couple of months ago - sorry for the picture quality, the mobile was all I had at hand.

    I will within short have it on wheels with an original transaxle gearbox mounted and a complete tail section.
    Image Unavailable, Please Login
     
  11. stratos

    stratos Formula Junior

    Dec 9, 2003
    639
    Switzerland
    #11 stratos, Oct 2, 2009
    Last edited by a moderator: Sep 7, 2017
  12. Dino Club Germany

    Dino Club Germany Formula Junior

    Nov 10, 2008
    549
    Germany
    Full Name:
    N. Schumacher
    On my Dino 246 I just found some weeks ago that the damper on the "front" end of the crankshaft was getting loose. That means the rubber between inner and outer metal part was going to loose its connection. The effect was that during flashing for the ideal ignition timing the line on the damper was "moving". After diassebling of the damper we saw that we could move the outer metal part with the ignition mark against the inner metal part for some mimimeter. I discussed the issue here with a lot of experts what options I have and if I could by just a new damper?. The outcome was for exactly the above mentioned reasons NO, and I have decided to rebuild the original one. This is in progress now at a specialist in Suisse. The price is around double than a new one would have cost, but I have the guarentee that the balance is exactly as it was before.
     
  13. sowest

    sowest Formula Junior

    Aug 18, 2006
    899
    Alex

    That is a very interesting project! Did you do the frame and panel fabrication yourself? I hope that you will share some pictures with us as you go along.

    Stratos

    That engine is a pleasure to look at. I have only seen one Stratos in person and I have never seen any of the mechanicals opened up. I didn't even think of the Stratos during this crankshaft discussion. It looks like the flywheel that you have pictured does not have the eccentric weight. Did the Stratos have a special internally balanced crankshaft? Maybe only on the rally cars? Did you ever have the two types of crankshaft side by side? It would be very interesting to see how the crankshaft counterweights differ between the two versions.

    Dino Club

    I think that you made the right decision. It might be possible to make a jig and match the offset balance of the new and old pulleys, but it might have been just as costly and there would have been more room for error.
     
  14. stratos

    stratos Formula Junior

    Dec 9, 2003
    639
    Switzerland
    Hello,

    You should loose the rubber-containing front pulley it can only create problems. Replace with solid item. The Stratos uses a normal Dino crankshaft and it's balanced with rods, piston-equivalent weights and flywheel attached. There is a special balancing process that I used to know some years back but have forgotten now. I will ask. In any case the balance is achieved externally and if you change your flywheel you need to rebalance.

    Regards.
     
  15. Alex_202

    Alex_202 Karting

    Apr 10, 2008
    66
    Sweden
    I understand the concept of an externally balanced crankshaft and that this is the case for the Ferrari 246GTS engine.

    However, what I have difficulty believing is that the flywheel has an imbalance. Flywheels are usually machined in a lathe, hence should be perfectly balanced.

    Has anyone tried to replace a stock flywheel with a new lighter one and perfectly balance one?
     
  16. champtc

    champtc Formula Junior

    Apr 18, 2004
    732
    I was told the exact opposite by my machinist this weekend. He told me that the Dino engine is Neutral balance & that the pistons & crank have to be balanced themselves which he did. He told me that they use "bob weights" to determine the rotational mass of the crank and also check the pistons as they do not move rotationally as they go in a vertical direction. Evidently this is all done on a computerized machine and they know how much to take off or put on the crank etc by way of the computerized readouts. I have not seen this machine but he said it is pretty common. He then balanced my stock flywheel which again he stated that since it is a neutral balance system that neither the fly wheel nor the pulley were to be used to offset the crank. When he balanced my flywheel he had to take some off & said that my pulley (a brand new one from Superformance was 60 grams off). He is doing the pulley now. I have been very curious about this so I was carefull to ask & record specific questions & answers. However that is what I have been told- others may disagree.
     
  17. dino clay

    dino clay Karting

    Oct 31, 2007
    185
    san mateo, cal
    Full Name:
    clay cavanaugh
    total confusion. I do balancing and have done it since 1965. There can be no confusioin as to external versus internal balancing and you only need to look at front damper and flywheel to decide this. If both do not have any signs of heavy sides, then you have an internally balanced engine. If this is the case, flywheel and front damper can be balanced individually with out being mounted to the crankshaft. In closing, all v configured engines, ie. v8 v6 need to be balanced using bob weights and the engine needs to be disassembled

    clay
     
  18. champtc

    champtc Formula Junior

    Apr 18, 2004
    732
    I think that we are both saying the same thing but you are doing so much more lucidly than I am!! I got my pulley back & he shaved some off to make it balanced (I guess there was a heavy side by 60 grams). My job now is to bolt all this together & see if I can get it to run!! I appreciate the education & clear explanation. Thanks
     
  19. Alex_202

    Alex_202 Karting

    Apr 10, 2008
    66
    Sweden
    OK, let me narrow my question down to the following:

    Is the standard 246 flywheel balanced in itself or not?
     
  20. sowest

    sowest Formula Junior

    Aug 18, 2006
    899
    #20 sowest, Apr 11, 2010
    Last edited by a moderator: Sep 7, 2017
    Anything is possible and there are exceptions to almost any accepted consensus, but I do believe that any standard 246 crankshaft requires an offset weight in the front pulley/damper and flywheel. The front pulley/damper and flywheel ARE NOT balanced by themselves.

    I do not have a flywheel handy, but I have enclosed a picture of a standard 246 front pulley/damper. The offset weight is clearly visible. The flywheel has a similar offset weight that is part of the casting. The casting is machined and then the offset weight is drilled, if necessary, when it is balanced as part of the whole cranshaft assembly.
    Image Unavailable, Please Login
     
  21. champtc

    champtc Formula Junior

    Apr 18, 2004
    732
    Perhaps I am wrong...has happened before but my machinist told me that the Dino engine is internally balanced (the crank & pistons are balanced amongst their rotating mass) and that the flywheel and Pulley are independent & neutral balanced. He explained that neither the flywheel nor the pulley are used to offset the crank & pistons. The pulley & flywheel are independently balanced so that they are in balance (not out of round). This is done without them being attached to the crank. I am enclosing a shot of my pulley pre balanced & post along with the original one (which is now junk as someoene welded it & screwed the whole thing up) & one of my flywheel which clearly has been drilled to offset whatever balance it had. So the story goes...
     
  22. champtc

    champtc Formula Junior

    Apr 18, 2004
    732
  23. sowest

    sowest Formula Junior

    Aug 18, 2006
    899
    Hi champtc

    I am struggling to find the words. I am having a hard time understanding how your machinist is coming to these conclusions. The original pulley and the new, replacement pulley have substantial eccentric weights. The original flywheel has substantial drillings on one side that give the effect of an eccentric weight. The factory did all this in error? Please check into this. I really do fear that you will be very unhappy if the engine is assembled with the parts that you have pictured. Perhaps it would be worth asking the machinist to spin the whole assembly on the balance machine before it is assembled into the engine. Maybe he modified the counterweights on the crankshaft. Please proceed with caution.

    I have not seen a lot of these cars, but every 246 I have ever worked on had the eccentric weights. Every 206 Fiat Dino that I have worked on had the eccentric weights. The only engine in this family that I have seen with an internally balanced crankshaft is the 206 FERRARI Dino. I am sure this was done because of the very special flywheel/damper assembly that is used in the 206 Ferrari.

     
  24. dino clay

    dino clay Karting

    Oct 31, 2007
    185
    san mateo, cal
    Full Name:
    clay cavanaugh
    that front pulley is an externally balanced pulley, no doubt
    be careful changing your fly wheel
     
  25. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,873
    #25 jselevan, Apr 12, 2010
    Last edited: Apr 12, 2010
    At the risk of adding useless information to an already confusing discussion, what follows is my understanding and observation.

    1) Flywheels are designed to be replaced without dismantling the engine. Hence, the flywheel should be balanced independent of other rotating components. "Wells" drilled into the flywheel FROM THE FACTORY are simply there to balance the flywheel. It is a large mass and a few grams here or there are needed to approach rotating balance.

    2) The front pulley is clearly offset (in every Dino I have seen). Pulleys from the factory, and new-old-stock pulleys DO NOT HAVE HOLES DRILLED IN THEM. If they do have holes drilled in them, a previous owner commissioned a machine shop to balance it independent of the flywheel, which would be incorrect. The offset balance of the pulley is there for a reason.

    3) All reciprocating components...pistons, wrist pins, upper connecting rods, and rod-end caps are all balanced to an equal weight.

    4) The crankshaft is balanced a) so that all rotational mass is concentric, and that all journals and counterweights are compensating each other, and b) then balanced with the front pulley to provide for compensation of a "see-saw" harmonic owing to the upward moving front piston and a dynamic force tending to bend the crank. The offset pulley will minimize this "3rd" harmonic force.

    Those that have holes drilled in the front pulley have lost this offset to a certain degree.

    Now, many of you will observe that you have holes in your pulleys. And many will reply that the pulley was balanced independent of the crank. That none of these engines have vibrated to destruction speaks for the relatively minor component provided by the pulley offset.

    I spoke with two "world-class" experts today, both of which stated that in an ideal world one should balance the crank and the pulley together (not the flywheel), but that they 1) never balance Dino engines because they are more than adequate out of the factory and 2) they would not lose a moments sleep over an engine that did have the pulley balanced independently. In fact, while we were talking, we looked at a 1973 GTS on the lift, and its pulley looked like Swiss cheese....clearly balanced incorrectly in the past. The car has 90k kilometers and runs like a dream.

    The take home message? Don't balance a factory Dino engine. If it has been balanced and has been running fine, don't balance it again. And if you have balanced incorrectly, enjoy the ride as it won't make a hill of beans difference. These are very smooth engines that don't rev to 18k RPM.

    Hope I haven't offended anyone.

    Jim S.
     

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