Flexplate and starter

Discussion in 'High Performance Modifications' started by vegas1974z28, Feb 17, 2021.

  1. vegas1974z28

    vegas1974z28 Moderator Staff Member Lifetime Gold Member

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    Can ANYBODY help me out? This has been going on for 10 years. I just purchased a 4 post lift, put the car up and what do i see......A broken tooth on the flexplate. This is my 5th flexplate and about my 10th starter. I have tried EVERYTHING. Spinning it before hitting the ignition, it has a start retard on it.....A starter only lasts 1 season. It kicks back boom ... It is a 12.5-1 496 and this is version 9 of the motor (all versions have had the kick back).....PLEASE any help...
     
  2. muscl car

    muscl car Veteran Member Lifetime Gold Member

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    That sucks Mattie. I thought you figured it out , have you talked with your engine builder over this issue
     
  3. muscl car

    muscl car Veteran Member Lifetime Gold Member

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    Mattie ..

    You're running locked out timing ... right ???? , could you have to much advance causing the engine to kick back or crank over slowly . What about the cam you're running could it be that it's been degreed wrong causing higher than normal cyl pressure


    Edit ....

    Talking to a friend of mine who's a mechanic and he mentioned this .....

    So he has it locked full advance?
    How much does it retard? Or should I say how much is it supposed to retard? Did he confirm the retard timing while trying to start it with the spark plugs out of it and the timing light checking the timing. If he has that thing around 38° total he’s retard should be down around 10 to 12. He’s got too much advance while it’s spinning over

    He also mentioned if it kicks back with the ignition off while starting you've got to much cylinder pressure


    Edit .....

    Didn't you have a timing chain cam sprocket failure were it sheared the bolts ??? , I can't remember if this happened on the top end or at the starting line at the hit . You might have a cam profile that allowing way to much cyl pressure and that caused the bolts to shear on the cam sprocket . You might look into this as it maybe the root of your problems

    This is his response about the cam sprocket bolts failure ....

    Yeah he’s got way too much cylinder pressure. Time for him to buy a new cam. And make sure he’s retarding with that ignition system. I would have him do research with a different profile cam in a different lobe center
     
    Last edited: Feb 17, 2021
  4. 80sz

    80sz Veteran Member

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    My gear reduction starter kept rolling back on my 11-1 small block also, got a start retard same thing 5,10 20 degrees didnt matter roll back chip teeth on starter or flex plate. Put in old starter no kick back. I feel it just spins to slow for big cylinder pressures. I don’t know about a high dollar brand as mine was a Jegs but good for 18-1. I still run stocker with 10.5 -1 ,idk if it crank 12-1 motor
     
  5. 80NastyZ

    80NastyZ Veteran Member

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    Have all versions of the engine used the same block ?

    -TOM
     
  6. vegas1974z28

    vegas1974z28 Moderator Staff Member Lifetime Gold Member

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    Yes Tom

    Thanks for the info Chuck, I'll talk to the engine builder.

    I don't think the old stock one will fit with the headers.

    Very frustrating, lost a final when the starter broke in the lanes.
     
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  7. 80NastyZ

    80NastyZ Veteran Member

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    Wondering if the starter face is not totally true 90 degrees in reference to the crank , on a stock or relatively stock engine it would make no difference as there wouldn't be enough compression to do damage . Only way to really tell this would be , well , you know …… :(

    I do know that I was having problems (Ignition related , of my own experimenting and doing) on my 496 that was in my '80 , it would kick back so hard it broke the ring off of two flex plates (TCI versions) .

    I bit the bullet and replaced it with a Meziere Billet flex plate and a Powermaster 9526 Starter which has the ability to mount with 3 bolts instead of 2 to try to remedy the situation , even with the kick backs until I figured out my issue it never hurt the flex plate , just tore up a replaceable drive in the starter.

    -TOM
     
  8. sandlapper

    sandlapper Veteran Member

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    Often, and in addition to timing, this type of complaint can be rooted in using wrong starter bolts.
    Correct bolts have both a knurl (grasps inside starter housing's bolt-hole and helps prevent starter-twist) ... AND a taper-step (block typically has chamfered hole and they mate-locate like lock&key and also helps prevent starter-twist).

    https://autoprollc.com/wp-content/uploads/2016/12/6-RemyTechnicalBulletin_Feb2016_web.pdf

    fwiw, most late model and hi-po starters use Permanent Magnets rather than field coils. That old trick of whacking starter to get the brushes to seat on commutator is bad idea on a PM starter. If you strike it sharply enough, it can & will crack the relatively fragile Cast PM inside; once cracked, their field is destroyed and starter's dead. Tshirt! Whacked starter on a briggs Vtwin rider; cracked PM & killed it!:(
     
  9. vegas1974z28

    vegas1974z28 Moderator Staff Member Lifetime Gold Member

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    Thanks for the responses. OK so with a new starter it turns like butter after a few kick backs the starter gets broke. That leads me to believe that the block is square. The bolts I use are the ones that come with the starter. I have used everything from the s10 mini starter to the MSD starter. I have had the engine on a stand and made sure the starter was engaging properly (paperclip). Could fuel leaking down into cylinders cause this?
     
  10. muscl car

    muscl car Veteran Member Lifetime Gold Member

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    Mattie ...

    I still think you've got to much cyl pressure and that's causing your kick back . As my friend suggests , does it kick back while cranking with the ignition off ???
     

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