72 Avanti flexplate

[donduck]

My Avanti is a 1972 Altman RQB1559. It was produced with a 350 cu in Vette engine & TH350 transmission. I am installing a rebuilt 350 Chevy and need to replace the original 153 tooth flexplate which has ring gear damage. It is different than 'standard' Chevy flexplates because it has a 7 7/8 diameter bolt circle to the six bolt torque converter. I was advised by Jon Meyer that the torque converter & flexplate may have been carried over from 327 cu in inventory and may be Power Glide components. Also. there is a possibility that they may have been Chevy truck components. Would the factory Build Sheet detail these components ? I have been in contact with numerous sources for flexplates and have 'struck out' everywhere. Can anyone help me with this snag ?

[Devildog]

My Avanti is a 1972 Altman RQB1559. It was produced with a 350 cu in Vette engine & TH350 transmission. I am installing a rebuilt 350 Chevy and need to replace the original 153 tooth flexplate which has ring gear damage. It is different than 'standard' Chevy flexplates because it has a 7 7/8 diameter bolt circle to the six bolt torque converter. I was advised by Jon Meyer that the torque converter & flexplate may have been carried over from 327 cu in inventory and may be Power Glide components. Also. there is a possibility that they may have been Chevy truck components. Would the factory Build Sheet detail these components ? I have been in contact with numerous sources for flexplates and have 'struck out' everywhere. Can anyone help me with this snag ?

I can not quite understand your 7 7/8 dilemma; however, another option is find the flexplate that fits and if the tooth count is different, change the tooth count on the starter. That 350 block will accept several style starter mounts as well. Alternatively, a machine shop can easily drill holes to fit what you need.

[Avanti83]

DD

Any of these help you out? http://www.summitrac...?Ns=Price%7cAsc

Bob

[Devildog]

DD

Any of these help you out? http://www.summitrac...?Ns=Price%7cAsc

Bob

Bob, where I am confused you say a 7 7/8 diameter bolt pattern. I thought the bolt patterns on ALL SBCs was 3 1/2 (or similar...have not measured). I have a flex plate from a 70-73 period 350 hanging on the wall and I think it is 3 1/2 diameter.

Joe

[donduck]

I can not quite understand your 7 7/8 dilemma; however, another option is find the flexplate that fits and if the tooth count is different, change the tooth count on the starter. That 350 block will accept several style starter mounts as well. Alternatively, a machine shop can easily drill holes to fit what you need.

[donduck]

I can not quite understand your 7 7/8 dilemma; however, another option is find the flexplate that fits and if the tooth count is different, change the tooth count on the starter. That 350 block will accept several style starter mounts as well. Alternatively, a machine shop can easily drill holes to fit what you need.

The 7 7/8 inch diameter is the bolt circle pattern of the flexplate to the torque converter that I want to retain. I believe that I am 'locked-in' to 163 teeth because the rebuilt motor only has the straight across starter mounting configuration.

[donduck]

Bob, where I am confused you say a 7 7/8 diameter bolt pattern. I thought the bolt patterns on ALL SBCs was 3 1/2 (or similar...have not measured). I have a flex plate from a 70-73 period 350 hanging on the wall and I think it is 3 1/2 diameter.

Joe

I think you are referring to the crankshaft bolt pattern. The 7 7/8 is the torque converter bolt pattern.

[donduck]

The 7 7/8 inch diameter is the bolt circle pattern of the flexplate to the torque converter that I want to retain. I believe that I am 'locked-in' to 163 teeth because the rebuilt motor only has the straight across starter mounting configuration.

I meant 153 teeth.

[Devildog]

I think you are referring to the crankshaft bolt pattern. The 7 7/8 is the torque converter bolt pattern.

OK, now I understand. i will ask around with our Corvette and older Chevy guys that may have an old PowerGlide flexplate or know where to find one.

[donduck]

OK, now I understand. i will ask around with our Corvette and older Chevy guys that may have an old PowerGlide flexplate or know where to find one.

Thanks Devildog

[WayneC]

I vaguely recall having that issue about 25 years ago, probably on my '71.

I think I bought a "correct" flexplate from Nostalgic Motor Cars.

Actually, my recollection is that the one I bought was sloppily done,

the converter holes apparently done with a hand drill by employees of the

Avanti Motor Company, but it did work fine (that steel is hard,

very difficult to drill).

But I agree with Devildog that if you can find a flexplate with the correct

crankshaft bolt pattern, diameter, and number of teeth, then a good

machinist should be able to drill the correct torque converter bolt holes for you

(since you have the old one to use as a pattern it should be easy).

I expect the machining would easily be within the 1-hour minimum most machinists

would charge for their work.

[donduck]

I vaguely recall having that issue about 25 years ago, probably on my '71.

I think I bought a "correct" flexplate from Nostalgic Motor Cars.

Actually, my recollection is that the one I bought was sloppily done,

the converter holes apparently done with a hand drill by employees of the

Avanti Motor Company, but it did work fine (that steel is hard,

very difficult to drill).

But I agree with Devildog that if you can find a flexplate with the correct

crankshaft bolt pattern, diameter, and number of teeth, then a good

machinist should be able to drill the correct torque converter bolt holes for you

(since you have the old one to use as a pattern it should be easy).

I expect the machining would easily be within the 1-hour minimum most machinists

would charge for their work.

Thanks for your responses Devildog & WayneC ---

I've been able to successfully drill a new 'generic' 153 tooth flexplate using the old one as a template. I now need to remove approximately 0 .075" from the welded torque converter mounting nuts because the new flexplate is 'dimpled' in the new locations causing interference. This is necessary in order to position the ring gear to its proper location. I think this will solve my dilemna. I only hope that all this is worth the effort instead of changing BOTH converter & flexplate to a current Chevy configuration. Does anyone have a clue why Altman Avantis used this converter ? Higher stall perhaps ?

Don Duck