727 flex plate?

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63SplitWindow

63SplitWindow

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Thought I spun a rod bearing but it turned out to be a broken flexplate.......what a racket that makes!
So now I'm on a quest to replace the broken unit. I believe this is an internally balanced 318 motor with a 727 with what looks to be about a 9" high stall converter.
I will verify that size when I get it out. Called Mancini to order replacement and he asked what size converter bolts, 5/16 or 7/16. I mic'd one of the bolts and it is 3/8".
They don't stock anything like that for a mopar. Not knowing who made this converter, how and where can I get a replacement?
I would have sworn this was an original Mopar flex plate but apparently not

20221003_140510.jpg
 
63SplitWindow said:
Thought I spun a rod bearing but it turned out to be a broken flexplate.......what a racket that makes!
So now I'm on a quest to replace the broken unit. I believe this is an internally balanced 318 motor with a 727 with what looks to be about a 9" high stall converter.
I will verify that size when I get it out. Called Mancini to order replacement and he asked what size converter bolts, 5/16 or 7/16. I mic'd one of the bolts and it is 3/8".
They don't stock anything like that for a mopar. Not knowing who made this converter, how and where can I get a replacement?
I would have sworn this was an original Mopar flex plate but apparently not

View attachment 1715993660
Click to expand...
Something like this might do the job:

www.summitracing.com

B&M 10230 B&M Flexplates | Summit Racing

Free Shipping - B&M Flexplates with qualifying orders of $99. Shop Flexplates at Summit Racing.
www.summitracing.com www.summitracing.com
 
63SplitWindow said:
Thought I spun a rod bearing but it turned out to be a broken flexplate.......what a racket that makes!
So now I'm on a quest to replace the broken unit. I believe this is an internally balanced 318 motor with a 727 with what looks to be about a 9" high stall converter.
I will verify that size when I get it out. Called Mancini to order replacement and he asked what size converter bolts, 5/16 or 7/16. I mic'd one of the bolts and it is 3/8".
They don't stock anything like that for a mopar. Not knowing who made this converter, how and where can I get a replacement?
I would have sworn this was an original Mopar flex plate but apparently not

View attachment 1715993660
Click to expand...
thats fixable :)
 
The B&M piece is a MUCH better part than a stock Mopar, and has a SFI cert if that is necessary.
3/8 is an odd size for a Mopar. I don't mean to insult, but are you measuring the bolt head, or the threads?
 
I just measured the clearance holes for the converter bolts on my spare B&M plate. .343 for the 5/16 bolts, .462 for the 7 /16.
 
mystery deepens......
After removing the trans to replace the flex plate, I discover the flex plate plate was modified to fit the crankshaft (see pics).
So after doing some research and test fitting to multiple cranks, I find out that my mystery motor has a 360 crankshaft (external balanced?) in a 318 block. So now the question is, what type of flex plate to get, since there are no weights on converter (like an external motor would) and a 360 cast crank?

20221004_125656.jpg


20221004_125126.jpg


20221004_125718.jpg


20221004_125816.jpg
 
Well first, that converter looks like a disaster. I would be looking for something else. Second, whoever put that mess together clearly didn't realize that mopars frequently used a bolt pattern with one hole offset, so it HAD to be bolted together in a certain way. This is especially the case with an externally balanced engine.
Third, I doubt that it has a 360 crank. The 360 mains are larger, so the 360 crank would have to be cut way down to fit a 318 block. Also, unless it was bored out all the way to 4.00" bore to use standard bore 360 pistons, it would have required custom pistons,because of the added stroke. lots of money.
Fourth, if it DOES have a 360 crank, unless it had a bunch of Mallory added to internal balance the 360 crank, if there were no weights on the converter or flexplate or balancer , it would have shaked your fillings out.
Looks to me like a lot more detective work is necessary. Does it have offset weight on the balancer?
Edit. Mopar flexplate has an offset hole in both the crankbolt pattern, and the converter pattern. Looks like the ear that broke off was the offset one.
 
Last edited:
33IMP said:
Well first, that converter looks like a disaster. I would be looking for something else. Second, whoever put that mess together clearly didn't realize that mopars frequently used a bolt pattern with one hole offset, so it HAD to be bolted together in a certain way. This is especially the case with an externally balanced engine.
Third, I doubt that it has a 360 crank. The 360 mains are larger, so the 360 crank would have to be cut way down to fit a 318 block. Also, unless it was bored out all the way to 4.00" bore to use standard bore 360 pistons, it would have required custom pistons,because of the added stroke. lots of money.
Fourth, if it DOES have a 360 crank, unless it had a bunch of Mallory added to internal balance the 360 crank, if there were no weights on the converter or flexplate or balancer , it would have shaked your fillings out.
Looks to me like a lot more detective work is necessary. Does it have offset weight on the balancer?
Edit. Mopar flexplate has an offset hole in both the crankbolt pattern, and the converter pattern. Looks like the ear that broke off was the offset one.
Click to expand...
Just got back from local trans shop to help identify this combo. Their best guess is, it looks like a Vega 9" converter that had been customized with anti-balloon plate and plates welded to adapt ring gear. Positively id'd the crank. Mopar 360 cast crank. Must have been machined down to fit 318 main journals. Not sure what pistons are in there.....I guess that will remain a mystery for now.
I just ordered a flex plate from CRT for a 360 crank. I will go from there when it arrives. Not sure what I will use for converter yet.
 
What does your front balancer look like?


A. 360 external balance:
1664915392082.png



B. 360 External Balance:
1664915545587.png


C. Internal Balance:
1664915824301.png
 
63SplitWindow said:
It has an aftermarket ATI damper on the front
Click to expand...

OK, wondering if the people who machined the 360 crank for the 318 block machined it to run internal balanced?

The way your re-worked torque converter is set up now, that is for internal balance with that 727 trans.
 
63SplitWindow said:
Just got back from local trans shop to help identify this combo. Their best guess is, it looks like a Vega 9" converter that had been customized with anti-balloon plate and plates welded to adapt ring gear. Positively id'd the crank. Mopar 360 cast crank. Must have been machined down to fit 318 main journals. Not sure what pistons are in there.....I guess that will remain a mystery for now.
I just ordered a flex plate from CRT for a 360 crank. I will go from there when it arrives. Not sure what I will use for converter yet.
Click to expand...
If you ordered a flex plate that is offset weighted for a 360 it will be wrong and will cause a vibration, if it truly had no vibration the way it was. The parts in your picture are for neutral balance.

How did you positively identify this as a 360 crankshaft; casting number? You said it was Mopar. If it was a Mopar Performance crankshaft it could have had a 318/340 main size with any stroke, so you’d have to measure stroke to be sure.
 
Bobzilla said:
If you ordered a flex plate that is offset weighted for a 360 it will be wrong and will cause a vibration, if it truly had no vibration the way it was. The parts in your picture are for neutral balance.

How did you positively identify this as a 360 crankshaft; casting number? You said it was Mopar. If it was a Mopar Performance crankshaft it could have had a 318/340 main size with any stroke, so you’d have to measure stroke to be sure.
Click to expand...
Yes, that is correct. I will have to figure out a flex plate / converter combo when it gets here.
I have a 360 motor with a stock mopar cast crank and the rear flange is exactly the same (pic).
I was hoping to avoid opening up this motor since I will be building a stroker motor over the winter from the other 360 block but again, you are correct.....I don't know the exact stroke in there.

20221004_183237.jpg
 
Why do you want to replace the converter? Do you have a question about drilling out the flexplate holes to match the converter bolts?
 
"I believe this is an internally balanced 318 motor with a 727 with what looks to be about a 9" high stall converter."

Are you even sure it's a 318 block?

Look above the starter on the block casting to see if it says "360".

Screenshot_20221005-055249_Gallery.jpg
 
Bolt on a new internal balance flex plate and go. Reuse your existing converter.

(provided you know for sure it's an internal balanced engine)

Screenshot_20221005-060101_Firefox.jpg
 
You have the wrong bolt pattern mopar flex plate to begin with.

20221005_062143.jpg


Has been modified with egged out hole.

Screenshot_20221005-061752_Firefox.jpg

More like this ^^^ bolt pattern is what you need.

Not this symetrical bolt pattern shown below.
Screenshot_20221005-061641_Firefox.jpg
 
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