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Thread: broken flywheel

  1. #1

    broken flywheel

    went to the track today and i started the car up let it warm up and drove it around the track but i heard a noise that didn't sound right so i shut the car off took the valve covers off too see if i had a loose rocker or something all look good put the covers back on and try to start the it made a half turn and got a little smoke out the carb and that was it. so i thought my starter had went out but i had a friend hit the starter as i look at the starter it was spinning the converter and flywheel but not the engine the flywheel center had broken all the way around. can any body tell me what may have cause this. it was a new sfi flywheel don't know the brand bolted to sbc and powerglide.

  2. #2
    Senior Member DYNO OPERATOR
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    Lot's of new parts and not enough checking

    If the torque converter was not fully engaged or lined up with the transmission oil pump prior to install in the car, the converter may have been stacked up on the pump and the flexplate may have been FLEXED with the converter forced against the flex plate due to the hub not engaged properly in the trans. If you have a new converter and have not checked the air gap measurement between the flex plate and the converter prior to bolt up of the converter to flexplate, you could have either a too large a dimension on the hub to mount lug dimension, which will push the converter in to the flexplate and cause trans failure and thrust bearing failure in the engine. This dimension is expanded the thickness of the mid plate when a mid plate is used to maintain the proper 3/16" to 1/8" air gap between the converter lugs and the flexplate prior to bolt up and after the trans is tight to the bell housing. Washers between the flexplate and lugs will not correct the improper hub / pump engagement. If the gap is too great between the two when checked, the converter must be cut apart and the dimension adjusted properly. The crank pilot must be fully engaged to allow the assembly to spin true. When you use washers between the flexplate and the converter you are taking away from the .20" or less engagement that the converter pilot usually has when dimensioned properly. This is the likely problem if the car has a mid plate and the converter is built for a non midplate application.
    There is about a 2% chance or less that you could have a bad flex plate but if it is new that is highly unlikely, very highly unlikely.
    Bruce

  3. #3
    Senior Member DYNO OPERATOR
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    OOPS, Found the problem

    I am sorry to report that I just read your previous entry on your torque converter. The large gap you asked about in your question is NOT OK and was the deal breaker for your flex plate. When you used washers to make up the gap you had, the pilot on the converter was removed from the crank that supports the converter and caused the bolts to try to hold the converter on center with the rotating assembly unsuccessfully. You can use washers as you were instructed to get the 1/8" gap, however there is a limit to how much gap you can make up with them. You must have 1/4" or more of washers stacked up I will bet. This is too much gap to make up with washers and will not allow the pilot engagement without extending the converter pilot dimension. The pilot on the converter holds a bearing that is pressed in and will release the bearing if you weld on it to extend it with a sleeve that some places will sell you to fix this problem. You are going to need a new pump bearing and seal at the very least prior to trying again. Tear down the trans pump and start over or your suffering will continue.
    Sorry to report this, but the cause is obvious now after reading you previous question.
    Bruce

  4. #4
    Senior Member DYNO OPERATOR
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    Not to hijack, but had a friend a few years back said his flexplate was broke, ended up being the tranny bolts were loose from the engine, LOL. At least it was easy.

  5. #5
    man this drag car is starting to be a big headache, i was told to get a better flexplate and a flexplate shim. so this will not fix my problem.

  6. #6
    Senior Member DYNO OPERATOR
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    Quote Originally Posted by bigmack
    man this drag car is starting to be a big headache, i was told to get a better flexplate and a flexplate shim. so this will not fix my problem.
    Like BEAST477 and jed5161 said in your earlier string, (torque converter question) You have to have the converter dimensioned correctly for your application. Shims will not help with the pilot engagement, they cause the pilot to be removed from the crank. That is bad for you and your flex plate. The flex plate could be stock and will last forever if properly assembled, It is only made to turn the converter, not to hold it on center. Sorry about what happened, but there is no short cut to the correct set up for your car, you need the correct dimensioned parts for your application.
    Bruce

  7. #7
    Senior Member MASTER BUILDER
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    Damn....
    It Ain't Over Til Its NOVA - 634ci of S*#t Your Pants!


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