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Thread: cracked flexplate?

  1. #1
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    cracked flexplate?

    While rebuilding the 425 in my 64 Riv we noticed the flexplate was cracked. I called about replacing it but was asked which one, should have a number on it, well it doesn't. But either way I was wondering if there was any major issue with welding it, I can sheet metal weld with the best of them but I don't know if welding a flexplate could cause more harm than good with balance, etc.

    Any thoughts on this would be greatly appreciated
    Rob

    1951 Chev Pickup
    1959 TR3
    1964 Riviera
    1965 Mustang drop top
    1970 Duster
    1976 Eldorado drop top

  2. #2
    Riviera addict RivNut's Avatar
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    Re: cracked flexplate?

    All nailhead flexplates that connect the crank to an ST400 transmission (64 - 66) are the same. You should be able to find a good used one. Check ebay for one.

    Ed

  3. #3
    Senior Member Rob J's Avatar
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    Re: cracked flexplate?

    I don't think I'd attempt to weld that flex plate. Remember that on a nail, the flex plate plays a part in balancing the engine. Also, remember to install the new flex plate correctly. It will bolt on 6 ways, but only one of them is right. There is a dimple on the crank flange, and that needs to be aligned with the small hole in the flex plate, otherwise you'll have a nice vibration issue.
    ROA Member #13099

    Link to Picture Album of Project Rivy 401 http://photobucket.com/65Rivy

    1965 Riviera 401, AC, Deluxe Interior (Currently undergoing a frame off nut and bolt restoration)
    1987 Buick Grand National (All original, and only 16k miles)

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    Re: cracked flexplate?

    Thanks for the input guys and good to know the alignment tip. I couldn't find anything on e-bay. The machine shop quoted $150 to weld and then put on a lathe to make sure it's balanced which I'm leary of. I'll have to check on a new on, also have some old contacts I'll have to look up and see if one of them has one.
    Rob

    1951 Chev Pickup
    1959 TR3
    1964 Riviera
    1965 Mustang drop top
    1970 Duster
    1976 Eldorado drop top

  5. #5
    Riviera addict RivNut's Avatar
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    Re: cracked flexplate?

    Nailheads are externally balanced. The crank, balancer, and flex plate have to be balanced as an assembly. Balancing the flexplate by itself won't do you any good. Go to the "Buick Buy/Sell" forum and ask who has one. Lots of guys frequent that forum who are "junkies" and scour the salvage yards frequently.

    I just checked Russ Martin's website. He's advertising new and used flexplates. I couldn't get the picture to open, but he says he has them.
    http://www.centervilleautorepair.com/BuickParts2.html


    Ed
    Last edited by RivNut; March 22nd, 2012 at 10:35.

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    Re: cracked flexplate?

    Thanks Ed! I'll look into those options
    Rob

    1951 Chev Pickup
    1959 TR3
    1964 Riviera
    1965 Mustang drop top
    1970 Duster
    1976 Eldorado drop top

  7. #7
    Senior Member JZRIV's Avatar
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    Re: cracked flexplate?

    The above info begs the question. If the flexplate is an active part of total engine balance, whats the chances installing one from a different engine requiring different flexplate balancing will cause a vibration problem?
    Maybe they are all close enough it doesn't matter. On the other hand we know there is apparently is some validity to how the plate is balanced because we've seen enough posts about vibration where the flexplate wasn't installed in the correct orientation as being the root cause.

    Where is your old plate cracked and how big is it. Depending how critical the area is where its cracked and how long the crack is would determine how practical it is to weld. If done properly and no additional weight is added from the weld you should be OK.
    Last edited by JZRIV; March 22nd, 2012 at 11:28.
    Jason Zerbini
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    Re: cracked flexplate?

    Quote Originally Posted by JZRIV View Post
    The above info begs the question. If the flexplate is an active part of total engine balance, whats the chances installing one from a different engine requiring different flexplate balancing will cause a vibration problem?
    Maybe they are all close enough it doesn't matter. On the other hand we know there is apparently is some validity to how the plate is balanced because we've seen enough posts about vibration where the flexplate wasn't installed in the correct orientation as being the root cause.

    Where is your old plate cracked and how big is it. Depending how critical the area is where its cracked and how long the crack is would determine how practical it is to weld. If done properly and no additional weight is added from the weld you should be OK.
    I was kind of wondering about that too, it all being balanced as a unit?

    The crack is about 2.5" long and more or less in the center between the crank hole and edge as I recall. It's at the builders so I haven't seen it lately but it's coming home this weekend
    Rob

    1951 Chev Pickup
    1959 TR3
    1964 Riviera
    1965 Mustang drop top
    1970 Duster
    1976 Eldorado drop top

  9. #9
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    Re: cracked flexplate?

    Quote Originally Posted by RivNut View Post
    Nailheads are externally balanced. The crank, balancer, and flex plate have to be balanced as an assembly. Balancing the flexplate by itself won't do you any good. Go to the "Buick Buy/Sell" forum and ask who has one. Lots of guys frequent that forum who are "junkies" and scour the salvage yards frequently.

    I just checked Russ Martin's website. He's advertising new and used flexplates. I couldn't get the picture to open, but he says he has them.
    Buick Parts


    Ed
    I sent an e-mail to CAR and they replied with no they don't. Sent a note to TA performance, they used to but I haven't heard back yet. Where is the Buick Buy/Sell forum? The classified section just has whole cars, don't have my secret squirrel password with me at work to log into the members only part, is it in the classified section there?
    Rob

    1951 Chev Pickup
    1959 TR3
    1964 Riviera
    1965 Mustang drop top
    1970 Duster
    1976 Eldorado drop top

  10. #10
    Senior Member Rob J's Avatar
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    Re: cracked flexplate?

    Call Rancho Riviera, and Tom Telesco to see if either one of them have one. I'd bet they do.
    ROA Member #13099

    Link to Picture Album of Project Rivy 401 http://photobucket.com/65Rivy

    1965 Riviera 401, AC, Deluxe Interior (Currently undergoing a frame off nut and bolt restoration)
    1987 Buick Grand National (All original, and only 16k miles)

  11. #11
    Riviera addict RivNut's Avatar
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    Re: cracked flexplate?

    The Buy/Sell forum is part of the Buick section. There are parts for sale as well as complete cars. Just start a new thread and ask who has a flexplate. Same admission as the ROA forum.

    Ed

  12. #12

    Re: cracked flexplate?

    As per Jason's balance comment-the flexplate is a relatively light component. The larger issue is with the heavy torque convertor that's bolted to it-especially any after market and 'rebuilt' units that either aren't balanced or are done poorly- and the convertor can be bolted up 3 ways and during engine r+r this should be marked, but often isn't. So, the flex needs to be on 'right' for locating the convertor 'right'-Dan Mpls. Mn.

  13. #13
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    Re: cracked flexplate?

    Thanks guys, I will follow up with those options.

    Ok Dan you got me nervous now, no I didn't mark the torque converter, I know the flexplate and crank have alignment marks (thanks Rob J) but how would I know which of the 3 possible ways to mount the torque converter?
    Rob

    1951 Chev Pickup
    1959 TR3
    1964 Riviera
    1965 Mustang drop top
    1970 Duster
    1976 Eldorado drop top

  14. #14

    Re: cracked flexplate?

    Bolt it up. If there's vibration, unbolt and rotate 120 degrees and try again-if still not right you have one more shot at another 120. Hopefully, you are in decent nominal balance and won't get into a problem with this-good luck!

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