Flexplate runout question

[Turbo6Smackdown]

Ok, I was staring at my rotating flexplate while the car was idling, and I can see what looks to be about maybe 3/8ths runout in that thing. What's acceptable?

 

[The Radius Kid]

Do you have the converter bolted up with it like that?

 

[Turbo6Smackdown]

Yep. It's all up and running.

 

[The Radius Kid]

Then I would say you have a large problem if the converter's bolted up and it's running out like that.
It should run dead true ... no questions asked.
I would suspect a bent converter snout from what you're describing.

 

[Turbo6Smackdown]

Oh. I see.

 

[Raeban]

I had a few of the cheaper SFI flexplates on a high compression SBC that had 1/8" of run-out even with the converter bolted up. Due to the high compression I would trash the teeth on the flexplate after a couple of months. My eventual solution was to buy a better flexplate and check the run-out first and even then I had to return one more. Another thing to watch out for is bent converter tabs. If the face isn't true on one of the tabs it will distort the flexplate. This may or may not be something you can remedy depending on how your converter bolts up, but before I pulled the trans i would measure the run-out with and without the converter bolted up.

All of that said, I never would have noticed the run-out on that engine if it wasn't for grinding the teeth off and a low compression engine would probably crank just fine. After checking several aftermarket flexplates I have little doubt there are more than a few people running 1/8" of run-out or more and not noticing it either. Especially with all the cheap converters out there that don't exactly have square tabs. If my car had 3/8" I would certainly be sorting it out but for all I know it might be one of those with 1/8" right now.

 

[Turbo6Smackdown]

Now that I look at it. I'd say it was more like a quarter inch. Is that ok?

 

[Raeban]

Now that I look at it. I'd say it was more like a quarter inch. Is that ok?

That really comes down to personal preference. No argument that no run-out is best. Sometimes the run-out comes from the flexplate ring gear not being square on the plate itself so the issue would likely be abnormal tooth wear. Out of curiosity how long have you been running this way? It is unlikely that this "just" happened so unless you changed something recently I suspect it has been that way for sometime and you never noticed.

 

[Turbo6Smackdown]

Same set up since 2009. Run about 50-100 miles since 09. No lie. So if there's more problems in my future they wouldn't have manifested themselves yet I'm assuming. Will this problem grow bigger do you think?

 

[hiboom]

My thoughts on this is if it's not chewing the teeth on the starter ring and no vibration is felt in the engine or drive train I'd drive it

 

[Turbo6Smackdown]

I got a lot of vibration in the engine lol. It shakes all over the place. Maybe it's hiding it?

 

[hiboom]

you can always disconnect the converter from the flex plate and see if it gets better if the run out is to bad I would think it would eventually make the front seal in the transmission start leaking .

 

[Turbo6Smackdown]

I see. Is there a way I could separate the two a little to prevent the converter tabs from hitting the plate? I would like to hope the converter was totally flat as it's a PTC. I expect nothing but the best from them. As for my seals, yes, I have leaks at every seal. Every single one

 

[John Larkin]

You can push the converter back at least 1/2" once it is unbolted. That flexplate should not wobble. Once you have it apart, find a way to bolt a piece of coathanger to one of the inspection bolts and then point it up to the flexplate almost touching. Then turn the engine slowly and watch the runout. Probably need someone up above the car to turn the bolt on the alternator, obviously with the engine off during all this.

 

[Turbo6Smackdown]

You can push the converter back at least 1/2" once it is unbolted. That flexplate should not wobble. Once you have it apart, find a way to bolt a piece of coathanger to one of the inspection bolts and then point it up to the flexplate almost touching. Then turn the engine slowly and watch the runout. Probably need someone up above the car to turn the bolt on the alternator, obviously with the engine off during all this.

What's an inspection bolt? And if I'm imagining this correctly, if the flexplate has no more runout, then it's the converter snout that's bent, and causing this runout because it's distorted the flexplate once it's bolted back up?

 

[John Larkin]

It holds the plastic cover on under the torque converter. I think there are 4?

 

[Turbo6Smackdown]

Ah. Inspection plate retaining bolts. Gotcha. I'll check 'er out and see what's up. Thanks.

 

[Turbo6Smackdown]

Ok. Checked the runout. Not as bad as it originally looked while running. It's about a quarter inch maybe less. Whaddya think?

 

[Raeban]

Well if the transmission front seal is leaking already I would go ahead and pull the trans to replace the seal and check the flexplate and converter tabs for straightness.