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Crankshaft length

Old 10-22-2018, 08:44 PM
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Crankshaft length

I'm in the midst of some confusion while installing a new create motor with a 700R4. While my converter is not seating into the tranny quite far enough, I noticed that the flexplate on my new Chevy Performance SP350/357 https://www.gmperformancemotor.com/parts/19367080.html sticks out more than on the 1990 L98 350 I am replacing. How is this possible? I can see that the new motor has what appears to be a longer crank coming out the rear before the flange that the flexplate bolts to. The shiny part (crank) you can see in the photo is not visible on the L98. How is this possible?


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Old 10-25-2018, 08:11 PM
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Re: Crankshaft length

I've got a LT1 sitting here and just measured the crank flange sticks out 0.3 in out from the rear main seal. You may want to measure both of yours and see if there's an difference and how much. I'm not sure how any crank could be different without a incorrect machining but then again I learn something new everyday.
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Old 10-25-2018, 09:57 PM
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Re: Crankshaft length

Thanks for checking! So it turns out it was a bit of an illusion. I took the flexplate off the L98 and the new motor. The crank flange is identical. For some reason the L98 flexplate is pretty much flat while the new flexplate is a bit raised in the center, causing it to be farther away from the block. Which is also odd. Both are standard flex plates. Not sure what to make of that.
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Old 10-26-2018, 04:09 AM
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Re: Crankshaft length

Originally Posted by bloodhound1 View Post
While my converter is not seating into the tranny quite far enough,
You MUST keep rotating the torque converter while pushing towards the tranny to fully seat it. They usually seat within 3-4 turns.

Also make sure the flexplate is not on backwards. The bulges out go towards the converter..... the converter's tabs DO NOT sit in a recess.

Last edited by NoEmissions84TA; 10-26-2018 at 04:12 AM.
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Old 10-26-2018, 11:08 AM
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Re: Crankshaft length

Originally Posted by NoEmissions84TA View Post
You MUST keep rotating the torque converter while pushing towards the tranny to fully seat it. They usually seat within 3-4 turns.

Also make sure the flexplate is not on backwards. The bulges out go towards the converter..... the converter's tabs DO NOT sit in a recess.
Yep, as you spin the converter it will click in three times.
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Old 10-26-2018, 01:47 PM
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Re: Crankshaft length

Originally Posted by NoEmissions84TA View Post
You MUST keep rotating the torque converter while pushing towards the tranny to fully seat it. They usually seat within 3-4 turns.

Also make sure the flexplate is not on backwards. The bulges out go towards the converter..... the converter's tabs DO NOT sit in a recess.
The new flexplate I got is nice enough to say "engine side" on it so it was definitely on the right way. It is just strange to me that the new one is more offset from the block than the old one, even though its a very small amount. Going to use the old one, even though its 29 years old. Teeth all look good.
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Old 10-26-2018, 01:53 PM
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Re: Crankshaft length

Make sure that converter is in all the way our you'll be installing a new trans
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Old 10-29-2018, 06:19 PM
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Re: Crankshaft length

Originally Posted by bloodhound1 View Post
Going to use the old one, even though its 29 years old. Teeth all look good.
Inspect the welds around the perimeter of the ring gear.
Inspect the area where the mounting bolts go in the center for any hairline cracks.
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