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Technical Sbc flex plate

Discussion in 'The Hokey Ass Message Board' started by 31Vicky with a hemi, May 20, 2019.

  1. Here are 2 168 tooth flex plates
    I believe the dark one is OEM
    The gold one is new

    Crank side up 00B49904-83E9-493B-8B0D-3DBC22E06BB0.jpeg
    ^^the center is on the table the ring is up
    vv the center is off the table
    263C42F0-77E0-46BD-92B1-51AB488E904C.jpeg

    Converter side up
    7BBB26C4-908E-41DC-B537-0E8ACBB92975.jpeg
    ^^ the center is just up off the table
    vv the center is close to the ceiling
    D76B245F-C804-4F55-9647-B1F2D4D568E3.jpeg


    It was sort of blind run down a rabbit hole to find the answer to this

    4C80482F-0DD6-4486-A799-A5D23CB7E006.jpeg
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 41,955

    squirrel
    Member

    I don't think the dark one is OEM, but that's only because I've taken a bunch of OEM flexplates off of Chevy engines. They all have flat centers, besides having engine color paint on them.
     
    31Vicky with a hemi likes this.
  3. That isn't a factory mini starter that had SAE shanks for bolts was it?
     
  4. Dick Stevens
    Joined: Aug 7, 2012
    Posts: 2,454

    Dick Stevens
    Member

    Is the first flex plate bent or is it just the angle of the photo?
     
    Deuces likes this.
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  5. No, it was a regular BIG body starter
    OEM rebuild. The freaking thing has a “rebuilt in China” sticker on it.
     
  6. Short version/
    Unknown car getting a lot of work done , one issue was a bad starter. Kinda worked with hammer tap.
    Get new starter
    Broke new starter
    Install 2nd new starter noticed the flex plate runout.
    Changed flex plate and had same run out
    Un bolt converter and it spins true,
    Washer shims between converter and flex plate cured run out, confirmed conveter tabs bent probably going to get new converter but let’s try it first, right?
    Very First drive for us around the block and massive first gear slippage. But second gear goes like hell, The trans has to come out.
    Pull the fucking thing. Set for rebuild.
    Installed a unknown th350 off the shelf here.
    No road test but it works in the shop.

    That’s not really short is it?


    The starter broke Thursday night after 4-5 starts, it was fresh out of the box. I saw China and figured they gave us a shitty casting nose cone.

    Put new starter in Friday night and could not get shimmed right. Noticed excessive run out on ring gear. Unbolt converter and it spins kinda funky- Shit !!! We need to change flex plate. This is my buddies car over here and I couldn’t do anything Saturday so he ran to summit grabbed the plate and swapped it Saturday. I didn’t observe anything. Until I got to the shop Saturday night and the new starter and new flex plate are doing the wobble and sorta bitching and definitely not playing nice.
    WTF,,, my buddy is heart broken as he worked on it all day to achieve nearly identical bad results.

    On Monday I screwed around with some shims and measurements. I installed .050 washers on 2 of the 3 tabs and got a flex plate rotation that was in the same zip code. Well IDK how or what but the converter tabs are bent somehow and needs a new one or benched and trued and at any rate the thing is coming out again.
    I figured we’d drive it once around the block to see what we have and the engine powers right thru first gear, the trans slips like hell in first. Ok for sure it’s coming out and going to be down for a few days.

    We yanked the trans and now I finally get to see both plates side by side.
    My buddy doesn’t have the time really, he’s kinda antsy so I tell him do you want to try a junk yard th350? I’ve got 2 but don’t know shit about them,, might work fine, might not.
    He takes the gamble and we stuck it in last night. Out in the shop way past my bedtime..

    I swear I get all the weirdest things come thru my door.
     
    VANDENPLAS likes this.
  7. partssaloon
    Joined: Jan 28, 2009
    Posts: 331

    partssaloon
    Member

    I've seen that a lot when a starter support strap wasn't used.
     
    olscrounger likes this.
  8. ^^^^^ My Son went thru several starters nose cones from timing at start up compounded by compression and lack of support.
     
  9. oldtom69
    Joined: Dec 6, 2009
    Posts: 362

    oldtom69
    Member
    from grandin nd

    I believe the starter I ordered was for 1965 big block-offset bolts and STEEL starter nose-have your parts guy pull one to check
     
    partssaloon likes this.
  10. treb11
    Joined: Jan 21, 2006
    Posts: 3,140

    treb11
    ALLIANCE MEMBER

    1 pc rear main seal or 2 pc? There is a difference. Crankshaft flange end runs true?
     
    VANDENPLAS likes this.
  11. oldtom69
    Joined: Dec 6, 2009
    Posts: 362

    oldtom69
    Member
    from grandin nd

    2 other problems that can bend flex plate= torque converter pilot not going into crank freely,trying to force it in with the bolts,or more common with a motor plate,converter pilot not long enough and not going into the crank at all
     
    olscrounger likes this.
  12. squirrel
    Joined: Sep 23, 2004
    Posts: 41,955

    squirrel
    Member

    that's a two piece seal type flexplate. They are quite different, enough that it's easy to see the difference if you know what to look for.

    So you guys need to build a transmission, eh? the starter might just be a symptom of that?

    and also find a quality flex plate, and rebuilt torque converter
     
    31Vicky with a hemi likes this.
  13. Someone before me clearly got something messed up. Maybe more than once.
    I’ve got a nice video of the chaos but I’ve not decided it needs to go to YouTube

    The old plate is dished - gear pushed to engine side. The converter is bent with at least one tab pulled towards engine more than the others.
    Made for a nice wobble in the ring gear.
    I’ve not grasped the forensics of the fuck up but there’s no telling what you’re going to find when following behind others.

    It’s really hard to look at an inoperative starter and see that condemnation of the starter, flex plate and transmission is warranted off the rip.
    Lots of coverage of the same ground over and over makes dynamite look like a great idea.

    Kinda like this
    The starter is not working
    Yep, $80, plus 1/2 hr.
    Ok
    We’re way the fuck off on that one
     
    Last edited: May 21, 2019
  14. There is and they will not interchange. Ya can’t innocently mix them up like you can a 400 flex plate. Since there is no limits on human ingenuity and stupidity I guess it’s possible to work hard and get the wrong one on lol
     
  15. Rich S.
    Joined: Jul 22, 2016
    Posts: 264

    Rich S.

    Show a pic of the back of the block and back of crank. Would like to confirm what type of seal.


    Sent from my iPhone using The H.A.M.B. mobile app
     
  16. I’ll try and remember if I got a pull the transmission out again. It’s a two piece
     
  17. squirrel
    Joined: Sep 23, 2004
    Posts: 41,955

    squirrel
    Member

    if those flex plates were bolted to it, it's a two piece seal. pretty obvious from here in Arizona.
     
    ffr1222k and Fordors like this.
  18. Rich S.
    Joined: Jul 22, 2016
    Posts: 264

    Rich S.

  19. squirrel
    Joined: Sep 23, 2004
    Posts: 41,955

    squirrel
    Member

  20. Rich S.
    Joined: Jul 22, 2016
    Posts: 264

    Rich S.

    Sorry Squirrel, that question was for 31 Vic. I know you know.


    Sent from my iPhone using The H.A.M.B. mobile app
     
  21. squirrel
    Joined: Sep 23, 2004
    Posts: 41,955

    squirrel
    Member

    he knows, too
     
    Johnny Gee likes this.
  22. Are you kidding me??
     
    BJR likes this.
  23. Thank you!
     
  24. Rich S.
    Joined: Jul 22, 2016
    Posts: 264

    Rich S.

  25. X-cpe
    Joined: Mar 9, 2018
    Posts: 483

    X-cpe

    Could the bow in the original flex plate been caused by the original installer not getting the converter all the way into the trans and then using the trans mounting bolts to draw the trans tight to the engine? Your description of the problem says that a couple of the converter mounting tabs were bent. Did you use that converter with the off the shelf trans? The fact you say that the flex plate runs true when the converter isn't bolted to it kind of says that the problem isn't with the flex plate or its mounting. Somehow freebies or helping a buddy out tend to be the time consuming jobs.
     
    olscrounger and brad2v like this.
  26. squirrel
    Joined: Sep 23, 2004
    Posts: 41,955

    squirrel
    Member

    the mounting tabs are rather stout, but converters are heavy, too...the only way I can see the tab getting bent is from the converter being dropped.

    It's a rather sucky situation, overall. My condolences.
     
  27. And that’s why some of this don’t make any kind of sense.
    The tab bent the other ways
    Up towards the snout
     

  28. Right now we have a different starter, flex plate, converter and transmission.
    This starter isn’t broken,
    This FP isn’t bent
    This converter doesn’t require washers
    This transmission moves the car and spins the tires in the shop.
    Waiting on road test

    Gamble on some time.
    $500 for bench rebuild vs a th350 in my pocket working or not. Went down like this - try it. If it works great if not it’s good practice swapping transmissions. All we loose is a few hrs
     
    Rich S. and ffr1222k like this.
  29. squirrel
    Joined: Sep 23, 2004
    Posts: 41,955

    squirrel
    Member

    Every TH350 that I've taken apart, even the good used ones, needed some parts replaced. But if the R&R is only an hour or two, it's worth the gamble, I guess
     
  30. VANDENPLAS
    Joined: Dec 14, 2009
    Posts: 1,647

    VANDENPLAS
    Member

    Had it a lot lately in heavy equipment running the 4.3
    That the cheap starters and starter bolts cause the starter to flex under load and wear the engine block mounting

    The cure for use has been to mill the starter mounting face down
    Shimming the starter
    Installing the rear starter mount bracket

    Also looking at the starter mounting holes are not cracked and the bolts are the correct shouldered bolts



    Ran into it once where someone installed a marine engine in a unit and flogged it off to one of my customers
    The crank was longer
    Could you have some kerfuckery going on?
     

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