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Discussion Starter · #1 ·
The original trans in my 57 Desoto with Poly V8 has a cracked case. Does anyone know if a 727 from the 70's will bolt up to that engine?
 

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From Wikipedia:

The Polyspheric or Poly engines were V8 engines produced by Chrysler from 1955 to 1958 as lower-cost alternatives to the Hemi engines. These engines were based on the Hemi engines, using the same blocks and crankshaft parts, but completely different cylinder heads, pushrods, exhaust manifolds and pistons.

They were called Polyspheric or Poly engines, because they featured polyspherical-shaped (meaning “more than one sphere”) combustion chambers. These combustion chambers were formed by the two shallow concave domes where the intake and exhaust valve seats were.

Because these engines needed a less sophisticated rocker setup, with only a single rocker shaft in each head, they were also cheaper and lighter than their Hemi counterparts. In the Chrysler literature, the Poly engines were also called single rocker shaft (SRS), while the Hemi engines were called dual rocker shaft (DRS).

These engines replaced Chrysler's flathead inline six in the division's lower-priced cars, but were slowly replaced by the Chrysler A engine, beginning in mid-1956.
 

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If it would fit the block there are numerous problems. Shifter, no emergency brake, drive shaft ( current one has a bolt on flange ) just to name a few.
 

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The original trans in my 57 Desoto with Poly V8 has a cracked case. Does anyone know if a 727 from the 70's will bolt up to that engine?
You can adapt anything to anything given enough time, tooling, and determination. But I would first look at your case snd see if the cracked case can be repaired. It may require the transmission to be disassembled prior to the repair depending on where it is cracked.

Then there is a option of finding a new case. Chrysler is more generally expensive then Ford and GM so I dont have much first hand experence with the 727.

If you want to run one then I would start with a 318 instead of the poly. I understand liking the old engine. The 68 wm300 I owned still had a flathead between the fenders and that was a very cool feature.

But as far as something you want to drive and find replacment parts for sometimes swapping a more popular engine/transmission like a 318/727 makes sense.

As far as the old transmission is concerned. I would get on a desoto or something similar site and see what they recommend. You may find a complete transmission or find firsthand advice on how to repair your old case.

If you cant find a specific forum there is always the ** bacon based 40-60's car forum. But they tend to look down on "modern" applications even if your talking 70's parts.
 

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Discussion Starter · #10 ·
Wow! I knocked the lid off a big can of worms . here. This was a simple yes or no question that turned into history of of Chrysler engines. I don't there was a clear just yet. Let me try this again. I have a 1957 Desoto Firesweep. It has a 325CI poly engine in it. The ORIGINAL trans has a cracked off ear on the band apply pin support. I want to know if a later model 727 has the same has the same bolt pattern as the old 488. Will the 727 bolt up to that 325 without an kind of adaptor?
 

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No.
The link I posted in #3 explains why in detail.

Short version is the dowel pins and crank flange are issues. The converter depth may also be a issue. Now you can modify things a bit to make it work.

But is it a bolt up deal. No.
 

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I have seen an adaptor on a Plymouth wagon but I don't recall the details. It's a very big change, however, as you have an 8-hole flange on the crank and need an adaptor ring on there with the 6-bolt fixing's threaded holes. And dowels. There was a cast adaptor ring between the block and the transmission.

But like I said, I'm not sure of all the details.

I would put this question, also the question of getting another original transmission, on the Forward Look forum. Those guys have this sort of thing sorted.
 

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Additionally, you can't readily describe Poly engines as one type of engine. De Soto and Dodge both had Poly engines which were Hemi blocks with a different head. This has been described above. But the other Poly engine type was the Plymouth engine known as the A-engine. This spread to other makes, of course, and it had essentially the same architecture as the later LA engines.

This was the engine called a 'wide block' by the unknowing types. Because the exhaust valves were vertical to the cylinders, and placed on the outer side of the cylinders, the rocker covers spread out further than those of the LA. The block was no wider at all.

The A-engine did come with the 8-hole flange on the crank until 1961, after that it had the 6-bolt tapped holes. The bolt pattern on the bellhousing also differed between the '61 and '62 models.
 

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Wow! I knocked the lid off a big can of worms . here. This was a simple yes or no question that turned into history of of Chrysler engines. I don't there was a clear just yet. Let me try this again. I have a 1957 Desoto Firesweep. It has a 325CI poly engine in it. The ORIGINAL trans has a cracked off ear on the band apply pin support. I want to know if a later model 727 has the same has the same bolt pattern as the old 488. Will the 727 bolt up to that 325 without an kind of adaptor?
No!
 

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Discussion Starter · #15 ·
Can you show a pic of the crack?
The pan is on it now. It's not actually a crack. Part of one off the bosses that a band apply pin goes through broke off. There are a couple of ways to fix it. I rebuilt trans for many years but just wasn't sure of the bolt pattern on the back of a 325 Poly engine. Since this is an all original well preserved one owner car, I'm the second owner now, I will probably fix the original trans.
 
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