Need help finding a stronger flexplate (custom?)

DMX

Registered User
I've destroyed one flexplate which in turn took out the transmission I had in at the time.

Pulling the engine to address another failed trans a couple of years later showed the new flexplate was cracked all around the crank mounting bolts.

Being that it's such a pain in the ~~~ to pull engine/drop subframe+trans just to change this part I'm hoping I can find something -MUCH- stronger to avoid dealing with this again.

Anyone know of a place that does custom flexplates? atiracing dashed my hopes today and I don't know where to turn.

Specs
1995 3.8 + 1994 M90 Blower (torque stress perhaps?)
Working on Internally balanced 4.2 Crank + custom rods and pistons
135 Tooth, 11.3" diameter external balance
F1DZ6375C
FRA-417 (parts america#)
 

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If the engine is internally balanced, why are you using an externally balanced flexplate? could that perhaps be the issue? Harmonic forces can create significant stresses in parts.

I've yet to hear of any such damage on a SC flex plate and there are some very fast SC motors with much more torque than stock using trans brakes and not tearing up the flex plate.
 
You guys are right, but i've already addressed that internal/external balance problem though.

back when I was using the stock balancer,crank and flexplate the flexplate was eventually destroyed.

After dropping in the sc crank and sc balancer+pulley, I knocked the balance weight off the flexplate (just a couple of small welds), a couple of years later I find that the crack all around the mounting holes .. on the way to another failure.

I should have been clearer, the factory piece is externally balanced, what I want is a spec(?) strength internally balanced unit.

I'm even considering buying two flexplates and welding the inner ~6" diameter of one to the center of the other, strengthening it where it seems to need it most.
 
Just because you knocked the weight off the externally balanced flexplate, does not mean that the flexplate becomes zero-balanced. I suspect is might be close, but I wouldn't count on it. Ideally, the engine should be balanced with the flexplate attached to the crank.

Although welding the center section of a second flexplate to the center of a new flexplate might increase the strength, it will be difficult to keep the welded assembly balanced and would be a bandaid, at best, for your problem.

Seriously, there are numerous SC's on this site making big power and torque, and I have never seen this problem posted before...not that some might exist.
 
Here is what you do. Get a stock replacement flexplate and then take it to a shop that can then machine and weld in a inner support plate, where you can find room that will re-enforce that area. You may need new bolts to bolt that on, and have to countersink them some in the plate you get so that everything will fit while giving you a bunch of support.

have the plate extend out as much as possible on the flex plate. Then grind on that such to relieve stress. The welds should be convex on the edges to prevent a stress crack at the weld.

Then have that unit zero balanced and true it up as it will warp some from the welding.

For certain, the problem you are having is highly uncommon to be non-existent in any other application of the M90. Don't discount that fact, as it could be highly likely you have some other problem there.
 
Your problem is installation related. I'll have to dig up the answer as I don't recall the specifics but it's definitely not a strength issue.
 
Are you still using the FWD block with the balancer shaft in the oil valley? Or are you using a RWD or SC block?
 
It could be installation related, I did take the time check and double check alignment, mounting holes and torqued down the converter to flexplate bolts in steps in a crisscross pattern, i'm not ruling out some obvious oversight though.

I haven't had much luck with machine shops in my area, my CNC crank pulley search is a recent example of the "we can't do that here"

I'd like to keep the area towards the outer edge untouched so the converter still gets "pulled out" the same amount, basically my thinking is just to artificially increase the thickness in the weak area.

Micah stopped by a couple of years back when I had the engine out and was struck by how small the Taurus flexplate is compared to SC units, I don't have any specs to compare but I wouldn't surprised if the sc flexplate was thicker as well. It seems like welding in the inner concave section would do the trick but you're the gurus :)


Balancer shaft was in place with the completely stock engine, I went ahead and left it in with the supercoupe crank but with the upcoming 4.2 boring balancing, matched pistons/rods etc I'll look into removing it if that's wise. And yes it was the Taurus FWD block, i'm building up a 2000 FWD Windstar block to drop in with the new stuff.
 
I would look into the possibility of a taurus SHO flexplate and see if it is different than the one you have.
 
The countershaft must absolutely come out and you need to have the whole rotating assembly balanced (by someone who knows what the hell they are doing). Very bad juju with your current combination.
 
Balancer shaft was in place with the completely stock engine, I went ahead and left it in with the supercoupe crank but with the upcoming 4.2 boring balancing, matched pistons/rods etc I'll look into removing it if that's wise. And yes it was the Taurus FWD block, i'm building up a 2000 FWD Windstar block to drop in with the new stuff.

oh boy... you gotta start taking a hard look at what you have done. Will it run, ala Junkyard Wars? Sure. Will it be reliable? Apparently not.

I really hope the machine shop didn't screw with the sc crank trying to balance everything with that balance shaft installed. I wouldn't be surprised if that balance shaft is the cause of all your problems. that will setup some terrible harmonic issues within your crank and might be the cause of that cracked flexplate.
 
Thanks for the help so far, there's only one shop I know of in town (Wilkerson's if anyone's heard of it) that does this boring/balancing etc I'm not even sure I want to go back there now after hearing all this. I distinctly remember hearing that the balance shaft didn't matter since mustangs didn't bother to use them (unverified claim), it didn't sound too unreasonable so I had them do the work.


Right now I just want some solid expert answers and it sounds like **proper** balancing more than anything else will extend flexplate life, is that all I should take away from this? Still doesn't explain the failure of the original part but that may just have been tired after 115K+ miles

I just want to know exactly what to tell them at the shop so I'm not back here a year from now with the same problem...

Again - internall balanced everything is the plan (4.2 crank, bhj balancer, matched custom rods+pistons that have been sitting over a year)
 
The only place I trust to balance a crankshaft for a Ford V6 is a place called Pro Comp Custom Engines in Springfield, OH. There is a very good reason for me saying this. It's worth shipping your parts to them to have it done right (I'll look up their # if you want).

I'm thinking there is another possible issue at work here. I have read about cracked flexplates somewhere that put it all in plain English but I can't seem to find it right now. I'm not going to make a statement without reading it again though because I just don't remember the details. There are specific things that cause cracks like that and it has nothing to do with engine power or torque.
 
If the transmission for some reason wasn't mounted flushly to the engine, or say some of the bolts loosened up slightly, that could cause a tug on the flexplate right? Just trying to think of other reasons for it, other than a faulty flexplate.

Could wheelhop from a FWD car cause this kind of failure?
 
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