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I am doing an LS7 427 conversion on my 79 Vette. I got the engine from my 2013 Corvette Convertible. It got a new engine under warranty. I bought the adapter I thought I needed and everything I read said I needed it. When I bolted on the LS flywheel, there was no obvious place for it. It would not slip onto the end of the LS7 crank. So I bolted the tranny to the engine without it. But when I installed the starter, there was a very slight interference between the flywheel and the starter. I was told that I needed to bolt on the GM spacer between the crank and flywheel. This spacer moves the flexplate back away from the engine and starter .400”. But when I go to bolt the transmission to the engine block, the torque converter binds with the trans while still .120” away from the block. The engine/torque converter totally binds when they are drawn the remaining .120”. Summit sent me a different, higher quality flat flexplate that does not interfere with the starter, but with the .400” spacer causes everything to bind still. Do I need this spacer? Without it, the torque converter will have to come out .300” from seated to bolt to the torque converter. Is that to far? Should I have .120” machined off of the spacer? Please help. GM spacer Adapter
Summit Advance Adapters 712500A
LS Series. Flexplate and hub extension, 168 tooth LS to GM transmission. The instruction sheet uses the hub extension only, so maybe I’m supposed to lose the Chevrolet Performance 12563532 .400” flexplate shim.
I disassembled and reassembled without the spacer, and took some careful measurements. The spacer is supposed to be .400”, but it is actually .410”. No biggie, it’s too fat at either measurement. I think the unicorns would fart rainbows and everybody would dance and sing with joy if this spacer was .300”. It would move the flexplate back to the converter, leaving room to expand when hot, and give the nose of the converter somewhere to park. The adapter is useless. I need to find someone to machine this spacer down to .300”.
Thoughts?
Bee Jay
I would like to see the torque converter (the side that bolts to the flex-plate) please.
Did you purchase a torque converter for a traditional THM700-R4 installation? (which is what I am guessing...) :-)
-OR-
Did you purchase a THM700-R4 torque converter intended for a LSx engine swap?
Last edited by vorteciroc; May 25, 2019 at 12:25 AM.
I’m using the 700R4 already in the car that was bolted to my 383. I race autocross regularly, and I was busting torque converters. So I had a special heavy duty 2500 rpm stall torque converter with lock up custom built. I’ve been beating on this tranny and torque converter for over five years and not a complaint. I’ll take pictures of the torque converter tomorrow.
I would like to see the torque converter (the side that bolts to the flex-plate) please.
Did you purchase a torque converter for a traditional THM700-R4 installation? (which is what I am guessing...) :-)
-OR-
Did you purchase a THM700-R4 torque converter intended for a LSx engine swap?
Here is the torque converter and crank end. LS7 crank end. 700R4 aftermarket torque converter.
The adapter was useless because there was a pilot bearing in the crank. Once removed the adapter slipped right in. This did not change the geometry though, the converter still has to come out 3/10” to meet the flex plate. The .410” spacer will still bond the engine transmission. The spacer needs to be .300” minus .125” converter free play. I need to have this spacer machined down to .175”. Check my math.
The flex-plate purchased is intended to be used as is, without the GM pilot support/ spacer that you purchased.
Two things are critical...
#1: The torque converter pilot is supported by the crankshaft. Either from the pilot support that was provided with the flex-plate or from the GM support/ spacer.
#2: With the torque converter fully inserted into the transmission pump assembly; a 1/8" space must be achieved between the flex-plate and the torque converter bolt pads.
Then the torque converter can be pulled towards the flex-plate and bolted together.
It would be more difficult to have the GM support/ spacer machined down (and actually be parallel) than using washers between the flex plate and the bolt pads of the torque converter and using the pilot support that came with the flex-plate.
I reassembled the engine/tranny/torque/ converter with two .090 shims and the adapter that gives the nose of the converter a solid place to park. The torque converter had to come out .120” to met the flexplate, damn close to 1/8”. I reinstalled the starter and everything seems fine now. I’m still curious as to why my combo binded with the .410” spacer, or why the torque converter had to come out so far without the spacer.
The flex-plate you purchased was manufactured to use the pilot support that was included with the flex-plate.
As such, the flex-plate you purchased is not intended to be used with the thick GM spacer/ pilot support.
Anyway... You got it all worked out with flex-plate shims. Great Job!
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LS7 to 700R4 help needed 
