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Crankshaft Extension Difference
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Powerflite
Posted 2013-01-16 5:26 PM (#355489)
Subject: Crankshaft Extension Difference



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Location: So. Cal		I know this has been stated before somewhere, but I can't seem to find it. What is the difference in cranshaft extension length between the later LA series engine and the earlier 392 hemi & other motors? I need to modify a later transmission adapter to use with the early motors and so I need to figure out how much to move things. Thanks.

Edited by Powerflite 2013-01-16 5:27 PM
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Mopar1
Posted 2013-01-17 10:41 AM (#355574 - in reply to #355489)
Subject: Re: Crankshaft Extension Difference



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Location: N.W. Fla.		If you have a pre '62 Non big block V8 and a post '61 tranny you get a 392 adaptor, I'd recommed Q.E.C., & everything bolts up, except for having to tap the crank flange holes.
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wayfarer
Posted 2013-01-18 7:54 PM (#355755 - in reply to #355489)
Subject: Re: Crankshaft Extension Difference



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Location: Peoples Republic of Oregon		Thanks Mopar1.

I find the OP's question a bit confusing.
If you already have an adapter for use with a later trans then what are you modifying and why?
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Powerflite
Posted 2022-12-07 11:23 AM (#626171 - in reply to #355574)
Subject: Re: Crankshaft Extension Difference



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Location: So. Cal		I still needed the answer to this question, but now I am able to answer it for myself. The top crank is from a 241 Dodge, the middle is a 4" stroker crank for an LA small block, and the bottom is a '58 318 A poly crank. The flange extension is the same on all the pre-'62 small block V8 engines and I measured it to be 2.03" from the back end of the flange to the inner end of the bearing flange. On the LA small block, I measured the same distance as 1.43". I can't measure it very accurately, but it looks like the rear bearing width is also the same between these three cranks.

So I get a difference of 0.6" between them.

Does that correspond to what others have measured? How about on the big block engines? Did they change by the same amount? Can anyone verify this?



(Crank Extension Differences.jpg)



Attachments
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Attachments Crank Extension Differences.jpg (194KB - 49 downloads)
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Powerflite
Posted 2022-12-07 11:27 AM (#626172 - in reply to #355489)
Subject: Re: Crankshaft Extension Difference



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Location: So. Cal		By the way, this stroker crank has 8 bolts for the flywheel. I guess you have to use a 426 hemi flywheel or flexplate with it.
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Mopar1
Posted 2022-12-09 11:14 AM (#626228 - in reply to #626172)
Subject: Re: Crankshaft Extension Difference



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Powerflite - 2022-12-07 10:27 AM

By the way, this stroker crank has 8 bolts for the flywheel. I guess you have to use a 426 hemi flywheel or flexplate with it.
Yup! any of the pre '62 non BB V8s uses the 392 adaptor & 426 Hemi flexplate. Long tail 331s have a slight difference vs the other 331s. There's no definate breakdown on numbers for long vs short tail cranks. A guy put a short crank in his long tail & had problems with his adaptors. Seems there was either a .200 or .020 diference, enough to cause problems.
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wayfarer
Posted 2022-12-26 1:53 PM (#626569 - in reply to #355489)
Subject: Re: Crankshaft Extension Difference



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Location: Peoples Republic of Oregon		I'm still not sure what the goal is....maybe a 4" crank in a pre-62 A engine?
If that is the case then there is no room for a block adapter unless you make a huge spacer for the crank flange.

The pre-62 crank flanges are a nominal 1.185/1.1875" from face of block to face of flange. There can/will be slight
variations in the measured distance due to the clearance at the thrust main and position of the crank.
The LA engines measure 0.5312" for the same face to face dimension.

As Mopar1 notes, the 51-53 crank is 0.200" shorter than the rest of the 331-354 cranks.
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