251 25in can fit in 1950 plymouth

[silvio84]

I accidentally purchased a 25in 251 speterfire engine for my 1950 plymouth and is 2 in longer. Any suggestions if I can put that engine into the car .

Thanks so much 

[Sniper]

I believe that's what they did with the Canadian Plodges (Dodge badged Plymouths).

[greg g]

The quick answer is yes.  But that depends on your skills etc, tools time, money, and patience.   Member Don Coatney documented the process of adapting a 251 DeSoto engine to his 48 Plymouth.  That info plus lots of photos are still available on this site.  Don unfortunately died several years ago, so you can't quiz him on issues.  Quickly, the radiator needs to be moved to the front of the dupport, front motor mount and frame may need modification.   You may need to run an electric cooling fan. If the new engine has a vibration damper you may need to notch and reinforce the front cross member.  If the 251 was set up with druid drive you will need to transplant bell housing flywheel and clutch parts from the old engine.  You may need to fabricate a new exhaust pipe depending on where the current exhaust manifold is located.  Some exit between 5 & 6, some exit to the rear of # 6.  You may need to modify the air supply for the heater. He also found that the 251 had a thicker crankshaft flange that prevented full engagement ofthe starter with the flywheel.   He had the bell housing machined to address this.

 

 

 

So it can be and has been done but it's not a bolt in swap.

 

What is the 251 out of, Chrysler,  DeSoto or Industrial? 

Edited April 9, 2023 by greg g

[silvio84]

Thank you Greg g for your help I will definitely look for member Don pictures to have more ideas .

Thank you  

[keithb7]

I have a 25” long 237 in my 1938 Plymouth. I bought it that way.Although I did not do the mods, I may be able to offer some photos and ideas 

 

 

[Sniper]

In the US parts manual,

 

all Dodge and Plymouth, 49-52 as well as all 6 cylinder Desoto and Chrysler's. 40-54 use the same engine front support plate, this is the part with the ears that bolts to the frame.  PN 854405

 

all Dodge and Plymouth, 37-54 as well as all 6 cylinder Desoto and Chrysler's. 37-54 use the same chain case cover plate.  This is the part that sandwiches between the block and the timing cover.  PN 688311

 

All DCPD 37-54 FL6's use the same insulator, goes between the two above parts.  PN 1405372

 

Since the engine mounting parts are the same let's look at the trans mounting.  This is somewhat complicated due to bellhousing and crossmember variations.  But one thing that stood out to me was the Frame Rear Engine Support Crossmember.  There are three varaints

 

P - 49-52
DCD - 49-52 (WITH FLUID DRIVE)
Dodge only 49-50 w/o FD

 

So what I can surmise here is that Chrysler left the front of the engine unmoved in either case but made up the 2" difference in the rear mounting.  Now if someone had a Canadian parts manual to double check...

Edited April 9, 2023 by Sniper

[kencombs]

24 minutes ago, Sniper said:

In the US parts manual,

 

all Dodge and Plymouth, 49-52 as well as all 6 cylinder Desoto and Chrysler's. 40-54 use the same engine front support plate, this is the part with the ears that bolts to the frame.  PN 854405

 

all Dodge and Plymouth, 37-54 as well as all 6 cylinder Desoto and Chrysler's. 37-54 use the same chain case cover plate.  This is the part that sandwiches between the block and the timing cover.  PN 688311

 

All DCPD 37-54 FL6's use the same insulator, goes between the two above parts.  PN 1405372

 

Since the engine mounting parts are the same let's look at the trans mounting.  This is somewhat complicated due to bellhousing and crossmember variations.  But one thing that stood out to me was the Frame Rear Engine Support Crossmember.  There are three varaints

 

P - 49-52
DCD - 49-52 (WITH FLUID DRIVE)
Dodge only 49-50 w/o FD

 

So what I can surmise here is that Chrysler left the front of the engine unmoved in either case but made up the 2" difference in the rear mounting.  Now if someone had a Canadian parts manual to double check...

The difference is in the location of the front mounts.  For, instance my 56 pickup frame is built in such a way that RH drive and 25inch engines could be install for export builds.  There are two sets of front mount holes in the front crossmember.  The rear mount doesn;t change, just the front mount and radiator location.

[Sniper]

Again, looking into the US parts manual. the cross member the engine support rests on is available separately and shows 1 part number for all Dodge and Plymouths, 49-52, 1149201.  No extra sets of engine mounting holes in it, one set.  Pretty sure the balancer would hit this cross member if the engine was 2" closer to the front of the car.  At least it looks that way on my 51 Plymouth.

 

Looking at frame assemblies, they boil down to three numbers in that time frame based on body style.  I see nothing about engines, but since the 25" engine was not available in the US they may not have bothered to list those numbers. 

 

Be interesting to look at part numbers from both the US and Canadian parts manuals to see what was, exactly, different.

[kencombs]

2 hours ago, Sniper said:

.  Pretty sure the balancer would hit this cross member if the engine was 2" closer to the front of the car.  At least it looks that way on my 51 Plymouth.

 

 

Yes it would.   'cause that chassis never had a 25" engine from the factory.  Many, many years ago I put a 251 in a car , think it was an early 50s plymouth, that had a 23.  Notched the crossmember.  Moved radiator to front of the support.  And drilled new mount holes.   But, the pickup like mine was designed for either as it was used in Oz, USA and Canada with local assembly changes.

[D35 Torpedo]

I can take some pics of my engine bay tomorrow if you like.

[silvio84]

On 4/9/2023 at 3:22 PM, keithb7 said:

I have a 25” long 237 in my 1938 Plymouth. I bought it that way.Although I did not do the mods, I may be able to offer some photos and ideas 

hello keithb

Thank you very much for answering, I saw your videos on YouTube, very good and instructive, thank you. I've been looking for a 218 but nothing near Florida in case one doesn't appear I'll have to go for 251, if you don't mind I'll ask you for help with some photos. thank you very much for your help

 

 

On 4/9/2023 at 3:22 PM, keithb7 said:

I have a 25” long 237 in my 1938 Plymouth. I bought it that way.Although I did not do the mods, I may be able to offer some photos and ideas 

 

 

 

[silvio84]

17 hours ago, D35 Torpedo said:

I can take some pics of my engine bay tomorrow if you like.

hi D35 you have 251 swap ?

yes please send me picks to have an idea

thanks

[silvio84]

On 4/9/2023 at 3:22 PM, keithb7 said:

I have a 25” long 237 in my 1938 Plymouth. I bought it that way.Although I did not do the mods, I may be able to offer some photos and ideas 

 

 

Thank you very much for answering, 
I saw your videos on YouTube, very good and instructive, thank you. 
I've been looking for a 218 but nothing near Florida in case one doesn't appear I'll have to go for 251,
 if you don't mind I'll ask you for help with some photos. thank you very much for your help

[D35 Torpedo]

8 hours ago, silvio84 said:

hi D35 you have 251 swap ?

yes please send me picks to have an idea

thanks

Hey just checking in now. Pics will have to wait till tomorrow now. I have a Canadian Dodge with a 25" engine. I think it's a 218.. but it shouldn't matter.

[FarmerJon]

To clarify: US plymouths and dodges got the 23" engines. The 217.8 US engines are typically referred to as 217".

The Canadian plymouths and dodges got 25" engines. These 218" engines are referred to as 218", but by exterior dimensions and features are identical to the Chrysler/desoto engines of the US, like the 251 you have.

 

What are your goals for the car?

Perfect restoration? Cruiser?

Hot Rod?

If I had a 251, I would run that over a 23" engine. Your stock plymouth had 97HP and 175 ftlb of torque. 

The 251s have 116HP and 208ftLbs, with only 7-1 cr. With some minor hop ups, power jumps up quick.

 

Good luck!

 

[silvio84]

1 hour ago, FarmerJon said:

To clarify: US plymouths and dodges got the 23" engines. The 217.8 US engines are typically referred to as 217".

The Canadian plymouths and dodges got 25" engines. These 218" engines are referred to as 218", but by exterior dimensions and features are identical to the Chrysler/desoto engines of the US, like the 251 you have.

 

What are your goals for the car?

Perfect restoration? Cruiser?

Hot Rod?

If I had a 251, I would run that over a 23" engine. Your stock plymouth had 97HP and 175 ftlb of torque. 

The 251s have 116HP and 208ftLbs, with only 7-1 cr. With some minor hop ups, power jumps up quick.

 

Good luck!

 

hello jon
I didn't know that in Canada they put 25in engines on the Plymouths, I have a question, is the front end longer or the radiator goes further forward because I was measuring and it's tight. I am putting this engine because I did not know that it was a 23in and 25in, I bought it without knowing, when I bought my car the engine was locked, I took it to the machine shop and they told me that they cut it to 060 over the cylinders has more damage and it cannot be fixed. I would like to leave the car in its original condition with the flathead engine.thank you Jon for the information 

[Sniper]

7 hours ago, silvio84 said:

hello jon
I didn't know that in Canada they put 25in engines on the Plymouths, I have a question, is the front end longer or the radiator goes further forward because I was measuring and it's tight. I am putting this engine because I did not know that it was a 23in and 25in, I bought it without knowing, when I bought my car the engine was locked, I took it to the machine shop and they told me that they cut it to 060 over the cylinders has more damage and it cannot be fixed. I would like to leave the car in its original condition with the flathead engine.thank you Jon for the information 

 

What the heck?

 

Why not just use the default font size and such?

[Dodgeb4ya]

But wait....that's so easy to read with out glasses.

[Sniper]

54 minutes ago, Dodgeb4ya said:

But wait....that's so easy to read with out glasses.

Maybe, if you were Mr. Magoo

[capt den]

i have a canadian parts manual 1953 and1954 if that helps.    dennis

[D35 Torpedo]

Here

[Jonathan]

I have a 1950 Plymouth p19 (likely Canadian made) and it has a 25 inch 251 in it.

[FarmerJon]

On 4/12/2023 at 7:08 AM, silvio84 said:

hello jon
I didn't know that in Canada they put 25in engines on the Plymouths, I have a question, is the front end longer or the radiator goes further forward because I was measuring and it's tight. I am putting this engine because I did not know that it was a 23in and 25in, I bought it without knowing, when I bought my car the engine was locked, I took it to the machine shop and they told me that they cut it to 060 over the cylinders has more damage and it cannot be fixed. I would like to leave the car in its original condition with the flathead engine.thank you Jon for the information 

If you want to keep your car original, the the 25" engine is not the way to go, even though, if done correctly, 99% of people would never know the difference. 

 

It is very difficult to accurately assess things like this thru the internet,  but I am curious what damage the shop found that prevents the rebuild of your original engine. There are .080 oversized pistons available,  and I belive some people have bored these blocks even more. Back in the '40s they made 'em thicc. 

If it is trashed, you should be able to find a core within a few hours drive of you.

 

I would think that properly listed, with decent pictures, you could resell the 251 to someone who needed it, or a hot rodder for your $ back or a small gain.

 

good luck!