Flexplate cracking!

[SVXRide]

Having just starting hearing the very familiar sounds of a cracked flexplate after less than 1k miles after replacing the "donut" flexplate that was in BillStock v3.5, I was wondering what other's experiences have been with the 4HEAT/EG33 flexplate. Is there a certain number of miles after which they will tend to crack? Are there any known contributors to the plate cracking (too much longitudinal play in the engine crank? slop in the trans? ) I'm seriously considering having a "beefed up" version welded together
-Bill (kicking himself for not installing a brand new flexplate....)

[Chiketkd]

Bill, sounds like dumb luck (or ill-luck) in this case especially since you installed a used flexplate as a replacement. Even though the SVX flexplate isn't the beefiest thing in the world, it has still held up to the power of LAN's and svxfiles' s/c SVXi!

From what I've seen, they tend to go out between 130-150K miles on several SVXs.

[SVXRide]

Originally Posted by Chiketkd

Bill, sounds like dumb luck (or ill-luck) in this case especially since you installed a used flexplate as a replacement. Even though the SVX flexplate isn't the beefiest thing in the world, it has still held up to the power of LAN's and svxfiles' s/c SVXi!

From what I've seen, they tend to go out between 130-150K miles on several SVXs.

Chike,
compared to the plates I'm used to behind sb chevy engines, our flexplate is a piece of aluminum foil . Adding the through holes only makes matters worse. I'm guessing the Subaru engineers were really looking to smooth out the driveline shock when the trans shifts, at the expense of life span under "non-stock" conditions. This is why I started this thread. I'm guessing any modification that makes the trans shift "harder" (small car kit, Tom K's resistor mod, etc.) will inherently put more load on the flexplate. I don't think LAN's car has had anything done to the way it shifts (but then I could be wrong).
-Bill

[Earthworm]

Think it's possible to stack 2 of them together or would there be clearance issues?

[cdigerlando]

Out of curiosity, where is it cracking?

[SVXRide]

Originally Posted by Earthworm

Think it's possible to stack 2 of them together or would there be clearance issues?

Tom K and I were discussing welding/riveting on a "washer" that has a diameter of at least 2x the current one (since the "knife edge" is where the flexplate flexes against the current "washer")

-Bill

[Beav]

Absolute #1 cause of flexplate cracking is the lack of alignment dowels between the block and transmission. The bolts don't align the two together, the dowels do. When the dowels are missing the crankshaft and torque convertor are not spinning on the same axis.

#2 'Hanging' the trans from the flexplate during install/remoaval. This bends the flexplate and causes wobble.

#3 Distorted convertor face from excessive lock-up clutch pressure or poorly rebuilt convertor (off-center stub.)

[SVXRide]

Originally Posted by cdigerlando

Out of curiosity, where is it cracking?

Chuck,
almost immediately below the "washer" plate that goes over the flexplate and the bolt go through to attach the entire assembly to the end of the crank. While not a perfect circular crack, it's very close to one.
-Bill

[SVXRide]

Originally Posted by Beav

Absolute #1 cause of flexplate cracking is the lack of alignment dowels between the block and transmission. The bolts don't align the two together, the dowels do. When the dowels are missing the crankshaft and torque convertor are not spinning on the same axis.

#2 'Hanging' the trans from the flexplate during install/remoaval. This bends the flexplate and causes wobble.

#3 Distorted convertor face from excessive lock-up clutch pressure or poorly rebuilt convertor (off-center stub.)

Beav,
Damn, damn, damn! Count my car as another victim of #1. One of the alignment dowels was actually missing when we pulled the trans, so I'm guessing only having one pin contributed to the first plate cracking. Figured the 4 bolts handled the alignment, so we didn't dig up another dowel when we installed the latest plate....crap!
Thanks so much for your insight on this...won't make this mistake again!
-Bill

[svxfiles]

I just now saw this thread and I must add that Bills engine/trans has had missing dowels before.
The last time we were in there we added the propper dowels, and made the best of the stripped engine threads as we could.
When I last spoke with LAN, I commented on the flex plate upgrade/fix, and of Bills continuing trans/motor mounting problems.
My idea for solving this type of power transfer problem is to use the two dowel holes as BOLT holes, giving six, where there was only four.

[TomsSVX]

Just be careful when you are trying to make a fix... Welding can weaken the thin metal substantially. A rivet might work well to secure a larger washer, just be sure the plate is flat. I feel that you have a large amount of crank walk at thise point, might want to look into it

Tom

[Beav]

The problem isn't the washer and using a heavier one won't change anything. Usually the broken portion of the flexplate is the identical size of the end of the crankshaft. It just seems that most washers are the same size, but not always.

Think about it, if it were truly just torque ripping the plate why would it only happen in one spot and in such a nice little circle? Why is Bill so lucky? (Sorry, Bill)

A heavier metal flexplate will probably only break exactly the same or cause the convertor shell to break. Or maybe worse - possibly transmit enough motion and vibration to the crank end and crack it (seen it happen to a 318 Dodge van), ruin the front pump housing and bushing or cause the bellhousing to break (seen that happen too.)

What I'm trying to get at is I think you're trying to fool a problem with a work-around and I'm afraid that will become more expensive in the long run. Something is out of alignment, whether it's missing dowels, a bad convertor (run-out, balance), improper engine or bellhousing face(s) (not really unusual) or possibly even a bad input shaft or poorly mounted front pump housing (or whatever is at the front of a Subie tranny )

[SVXRide]

Originally Posted by Beav

The problem isn't the washer and using a heavier one won't change anything. Usually the broken portion of the flexplate is the identical size of the end of the crankshaft. It just seems that most washers are the same size, but not always.

Think about it, if it were truly just torque ripping the plate why would it only happen in one spot and in such a nice little circle? Why is Bill so lucky? (Sorry, Bill)

A heavier metal flexplate will probably only break exactly the same or cause the convertor shell to break. Or maybe worse - possibly transmit enough motion and vibration to the crank end and crack it (seen it happen to a 318 Dodge van), ruin the front pump housing and bushing or cause the bellhousing to break (seen that happen too.)

What I'm trying to get at is I think you're trying to fool a problem with a work-around and I'm afraid that will become more expensive in the long run. Something is out of alignment, whether it's missing dowels, a bad convertor (run-out, balance), improper engine or bellhousing face(s) (not really unusual) or possibly even a bad input shaft or poorly mounted front pump housing (or whatever is at the front of a Subie tranny )

Beav,
The more I think about this, the more I agree with you Having a thicker flex plate probably wouldn't hurt (I've measured and you can only double up the thickness and still bolt it to the TC), yet - as Tom J noted - you'd have to be careful on how you attached the additional metal, and, I agree it would only delay the eventual same failure mode we're seeing now. With any misalignment of the trans and engine comes a off-axis loading on the flexplate, which means that it loads against the end of the crank. Given that the assembly is rotating, this explains (I believe) the fact that the crack ends up being almost perfectly circular in nature.
So, we live and learn and, hopefully, don't repeat our mistakes
Thanks again for your insights!!
-Bill (off to get a new flexplate and alignment dowels )

[jman050]

Originally Posted by SVXRide

Beav,
Damn, damn, damn! Count my car as another victim of #1. One of the alignment dowels was actually missing when we pulled the trans, so I'm guessing only having one pin contributed to the first plate cracking. Figured the 4 bolts handled the alignment, so we didn't dig up another dowel when we installed the latest plate....crap!
Thanks so much for your insight on this...won't make this mistake again!
-Bill

How many miles did the flexplate last without the dowel?

[SVXRide]

the first flexplate had around 40k on it before its loading condition changed...I got the second flexplate from Tom J, so I don't know how many miles it had on it.
-Bill