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Old 09-07-2010, 05:43 PM
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Can't stop warping Flywheels and eating th350's

Hey guys I got a Roller 355 with 386hp and 468 Torque. I can't seem to keep a flywheel from warping in there. I'm going on my 3rd one already. It has a new starter and new transmission. The 1st tranny cracked and the second one got the internals completely worn out. The 3rd has B&M clutches and is so far holding fine. The drive shaft is brand new. The rear end has 3.52's, and all new bearings.

Thanks,
JD

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Old 09-07-2010, 06:36 PM
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By flywheel, I assume you mean the flex plat to which the ring gear and TC attach. Have you tried an SFI rated piece? I believe they are a smidgeon thicker. A very little bit of extra thickness can double the stiffness.

Pat
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Old 09-07-2010, 06:41 PM
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I'll have to give it a shot

Thanks for the reply I'll give it a shot. Any idea on price by the way?

Thanks,
JD
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Old 09-07-2010, 06:54 PM
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Quote:
Originally Posted by 355Nova
Thanks for the reply I'll give it a shot. Any idea on price by the way?

Thanks,
JD
In the $40-75 range depending on where you shop, and brand.
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Old 09-07-2010, 07:13 PM
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Could also be an engine to transmission alignment issue. Where did the case crack on the transmission. If it was in the bell housing area this is a definite possibility. You do have both alignment pins installed correct.
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Old 09-07-2010, 07:18 PM
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Pins are aligned correctly. The crack was on the tail housing area. I even want as far as unbolting the flexplate from the converter making sure to see if the converter was not warped some how. This happens after a while of driving car around. Been about a month since I installed this one.
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Old 09-07-2010, 07:27 PM
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I would check the flange on the crank to make sure it is clean and flat so the flywheel is sitting flush.
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Old 09-07-2010, 07:35 PM
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Pat is talking about a SFI 29.1 flexplate.
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Old 09-07-2010, 07:37 PM
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Quote:
Originally Posted by T-bucket23
I would check the flange on the crank to make sure it is clean and flat so the flywheel is sitting flush.
Yeah, and attach a dial indicator off the crank and swing it 360 around the block where the bellhousing bolts up to check for concentricity. The rear surface of the block might not be perpendicular to the crank centerline.
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Old 09-07-2010, 08:38 PM
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Look at the torque converter. If the crankshaft bolts are leaving there imprints on the torque converter then the converter is "ballooning ". I may be completely off base here ,however i have seen it take out front pumps and thrust bearings.Just a thought
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Old 09-07-2010, 10:45 PM
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Years ago a friend of mine had a 4 bolt 350 that did this very same thing. Whoever had the truck before him went all out on the build. Forged steel crank, camel back heads, forged pistons, small cam, weiand intake, holley carb, headers and other goodies. Behind it was a TH350 that I rebuilt when he first got it, a line had broke, he ran it low on fluid and it cooked the tranny. I was taking auto tranny`s in tech college at the time so I used it as my rebuild for the quarter which was required by all students.
The truck was a 78 chevy short wheel base step side, it was slammed (lowered) and had real nice deep Ultra swirl wheels with really wide dunlop 50 series rubber, it was beautiful pearl white with a nice black snap on bed cover. On the steps and tailgate it had chrome pieces inlaid, the tail lights were made into the rear fenders and lastly a stull chrome grill, it was really a sharp truck, but it was nothing but one problem after the next.
One day he calls me and tells me the starter went out, so I go help him replace it, that didn`t fix it, so the flexplate is bad, we swap it and in 2 weeks the flexplate was broken and cracked, and when they crack they sound identical to rod knock. So out comes the tranny again, replace the flexplate, in 2 weeks same result. Out comes the tranny again, this time I check the dowel pins, they are good, still fit tight to the tranny, checked the converter, it was fine, checked the crank flange, clean and looked good. Fired up the engine and looked at the crank while it ran, by eye it looked fine. So we put it back together, this time I made sure everything was torqued down to spec. Once again 2 weeks later the flexplate was cracked again. Soon afterwards, the truck developed a seperate problem so it was sold. Later on after some bargaining he got the engine back and we used the forged crank in a different block. It ran fine without issue for thousands of miles so I never did figure out what was causing it to eat flexplates.
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Old 09-07-2010, 11:05 PM
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just an observation/comment, DV I know you said you checked the TC but...

Latech mentioned it and:

common denominator = convertor reused in each case. 468 ft/lbs is allot of twist, 355 what do you know about the convertor new/used/stall/make/size
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Old 09-08-2010, 04:15 PM
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cracked tailhousing- probably not realted to what's breaking the flexplate, but that's usually a driveshaft problem or something like running a stiffer tranny mount than motor mounts... broken motor mounts maybe?

Flexplate- top suspect is the converter, if one of the tabs is a little off it would have the same effect as a crank CL that is not perpendicular to the bellhousing flange. Other things to check, i like techinspector1 suggested, is the bellhousing fange flat/perpendicular, and is the matching flange on the tranny right? is something else getting in between the tranny and the engine during assembly (are the mating surfaces clean and flat, no nicks, I knew of a car that was having similar problems that the owner managed to pinch a vacuum hose in between the 2 2x in a row). Does the crank have any burrs or anything else that's keeping the flexplate from bolting up flush?
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Old 09-08-2010, 08:27 PM
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Ok I checked the tranny before unbolting from block and looked fine. There was nothing in between. I took the flexplate off and nothing keeping it from seating flush. I took the flywheel back to autozone and told them I bought it that way, and they replaced it. I put the new one on looks flush.

The converter is a new one with the rebuilt tranny. On the other th350 I had the converter was rebuilt and it also did the same thing.

I have a good feeling this one is going to warp as well.
If it does warp I'm going to try a SFI flexplate.
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