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Flexplate gap bbc

General engine tech -- Drag Racing to Circle Track

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Jatmobkar
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Flexplate gap bbc

Post by Jatmobkar »

I switched to a sfi flexplate on my new 454 build. I have .093 air gap between flexplate and converter. Called coan and they don’t seem excited about milling the pads. Is this normal or what? I can’t get a straight answer on what to do. With the stock flexplate I had .125
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Re: Flexplate gap bbc

Post by miniv8 »

If everything is correct, the converter bosses must be configured for a midplate.
A novice machinist with a lathe can clean it up for you.
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Re: Flexplate gap bbc

Post by GARY C »

Jatmobkar wrote: Sun Jan 12, 2020 3:07 pm I switched to a sfi flexplate on my new 454 build. I have .093 air gap between flexplate and converter. Called coan and they don’t seem excited about milling the pads. Is this normal or what? I can’t get a straight answer on what to do. With the stock flexplate I had .125
I always ran a washer on my SBC stuff that would take up most of the space and a big enough diameter to cover most of the mounting surface. I have seen some guys just draw them up tight, probably why you see guys with cracked flexplates.
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Re: Flexplate gap bbc

Post by BillK »

Is .093 a problem ??? If you were using a stock type flex plate before there is a good chance it was not very straight anyway. I have always figured that as long as there was some clearance it was good to go.
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Re: Flexplate gap bbc

Post by Coloradoracer »

SFI flexplate is thicker than stock. That explains the difference. DO NOT shim the converter away from it. You need that room to prevent the converter from bottoming out in the pump. You can have the pads machined down on the converter for additional clearance if you need it. SFI flexplate won't flex as much as a stock one though. I've never had an issue with this.
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Re: Flexplate gap bbc

Post by tenxal »

Jatmobkar wrote: Sun Jan 12, 2020 3:07 pmI switched to a sfi flexplate on my new 454 build. I have .093 air gap between flexplate and converter. Called coan and they don’t seem excited about milling the pads. Is this normal or what? I can’t get a straight answer on what to do. With the stock flexplate I had .125
I've run as little as .100 on mine with no issues. In a pinch, I'd run it.

If not, set it up on a mill, take .030-.035 off and sleep better. Little details like this are what bite you later. :wink:
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Re: Flexplate gap bbc

Post by rebelrouser »

I would go with the .093 gap as well. All that is needed is for the pump drive not to bottom out in the pump housing and tear metal off. Good converter that does not balloon and a ridged flex plate, you should have no issues. I am not sure how the converter companies jig their units before welding, but I seldom see the same gap from converter to converter. Most of the time if there is an issue I get nervous, is too large of a gap and have to add washers. Mopar transmissions have the shortest distance in the bell housing, and many times I have gotten converters that had no clearance.
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Re: Flexplate gap bbc

Post by Dave Koehler »

For being so persnickity about other things I feel bad that I never measured that clearance.
I never saw the need.
Heck I never saw a spec written on this.
As long as I had some everything always worked like it was supposed to.
Chances are if it is .093 on one pad it might be .150 on another due to the "flex".
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Re: Flexplate gap bbc

Post by 77cruiser »

I had one that ended up at .065, but ran it, it was OK but I pulled it & had it restalled & thought I told the conv. gut to take .030+ off but he didn't.
Chucked the snout in the lathe & to some off myself.
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Re: Flexplate gap bbc

Post by shoedoos »

^^^^^^ off the snout?
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Re: Flexplate gap bbc

Post by tenxal »

77cruiser wrote: Mon Jan 13, 2020 4:05 pmI had one that ended up at .065, but ran it, it was OK but I pulled it & had it restalled & thought I told the conv. gut to take .030+ off but he didn't.Chucked the snout in the lathe & to some off myself.
Shortening the convertor hub would decrease the convertor-to-flex plate clearance, assuming the convertor hub was 'bottomed' in the crank counter bore.

Which they rarely are........
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Re: Flexplate gap bbc

Post by 77cruiser »

tenxal wrote: Mon Jan 13, 2020 5:17 pm
77cruiser wrote: Mon Jan 13, 2020 4:05 pmI had one that ended up at .065, but ran it, it was OK but I pulled it & had it restalled & thought I told the conv. gut to take .030+ off but he didn't.Chucked the snout in the lathe & to some off myself.
Shortening the convertor hub would decrease the convertor-to-flex plate clearance, assuming the convertor hub was 'bottomed' in the crank counter bore.

Which they rarely are........
Took it off the pads.
Jim
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Re: Flexplate gap bbc

Post by tenxal »

77cruiser wrote: Mon Jan 13, 2020 7:04 pmTook it off the pads.
Got it! :)
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