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Installing a P25 Plymouth engine in a 1934 Dodge pick-up


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I have a 1934 Dodge pick-up that I've owned for many years, and finally decided to get it back on the road.  The original engine was rather tired, so I decided to update to a later 218 or 230 inch flat-head backed by a 5 speed transmission from a Chevy S-10.  I found a decent '54 Plymouth engine, and started the disassembly.  I did a similar swap (without the 5 speed) years ago with a '57 Plymouth engine in a 1936 Dodge pick-up.  That swap was a simple engine replacement with no issues.  With the '34, there are issues.

 

My first issue is that the '34 and '54 engine blocks are slightly different.  The lower part of the block, just above the pan rail, the left side of the engine is wider on the '54 engine.  With the original '34 bell housing installed on the '54 engine, there's no way to install the original '34 starter.  It interferes with the wider engine block.  I do have a '46 bell housing that I could use, but that would require me to fabricate a different rear engine mount, different clutch linkage and starter pedal linkage, and to figure out what to use for a throw-out bearing. Obviously, I would really prefer to use the '34 bell housing. I hoped I could find a small, high torque, mini-starter that would fit.  I have found a lot of starters on the web, but I can't find any details/dimensions to determine if they would fit my engine/bell housing combination.  Does anyone have any information on a starter that would work for my engine/bell housing combination?

 

My second issue is that the oil pans are different on the two engines.  The truck has a cross member that fits between the oil pan and the flywheel.  The sump on the oil pan of the '34 engine is shifted about 1.5 to 2 inches forward to clear the cross member.  My hope is that I can simply swap oil pans.  However, I don't know what differences there may be in the oil pick-up/screen, or other parts inside the pan.  Any insights or guidance would be appreciated.

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Kinda sounds like your custom powertrain will need more customizing...the issues you describe do not surprise me as flathead development was an evolutionary process, and not everything is backwards compatible.  I am guessing that your custom engine mounts and linkages will be easier to come by than finding a specialized starter.  FWIW, I have a '54 Plymouth 230 in my '48 1/2 ton, and it has the truck oil pan and oil pickup to clear the steering rods.

additional information - flathead oil pan clearance

additional information - flathead oil pan differences 

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JB when you swapped your oil pan from rear to front sump what did you do for the dip stick hole in the block?  It's not a threaded hole how did you plug it? Doing the same.

Thanks

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The bolt pattern for the oil pan is the same for both engines. If you can move the oil pick up in your P25 engine to match the location of the original 34 engine then you should be able to use the original oil pan (and probably dipstick).

 

With respect to the starter, that is the same issue people have putting later engines in 1933 and 1934 Plymouths. The two solutions I have heard of are: 1) Grind the side of the original 1934 starter to get it to fit. 2). Mill the bell housing or make an adaptor to move the starter to the position used in 1935 and later engines.

 

Question: If you are using the flywheel off the P25, does it have the same number/size teeth as the original 34 flywheel? I have heard that sometime in the 1950s they changed that up. That may affect your decision about what to do with the starter.

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8 hours ago, Boody said:

JB when you swapped your oil pan from rear to front sump what did you do for the dip stick hole in the block?  It's not a threaded hole how did you plug it? Doing the same.

Thanks

According to Dad, the engine was swapped years before I existed...on front sump engines, the block has a metal plug similar to a welch plug in place of the dip stick tube.  A possible solution is to tightly fit a short bolt or headed pin set in black RTV.

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  • 2 weeks later...

An update on my engine swap efforts.  First, my thanks who provided comments: they did help.  The oil pan swap was, as I hoped, a fairly easy change.  The sump on the '34 oil pan is only about 2 inches forward of the location on the P25 pan.  Internally, the baffling in the pan, and the oil pick-up screens were quite different.  Fortunately, the oil pick-up location was the same on both engines is the same, and the pan went on with no problems.  The hardest part was all the cleaning, and getting the gaskets properly fitted.

The starter problem took a little more research.  I found that the early hemi V-8 (1951 to 1955), like the early flathead 6 cylinder engines, used a 146 tooth flywheel, and a starter with a 9 tooth pinion.  They also both mount into a 3.25 inch opening in the bell housing, and the mounting bolt pattern is the same.  While a couldn't find a listing for a mini, gear reduction starter for a flathead, they are available for a hemi.  I bought a starter from "Promaster", and, with a little grinding on the block for clearance, it bolts into place.  (I could have ground the starter mounting flange, but was reluctant to take a grinder to my new starter.  I did the test fit on scrap/cracked P15 block.) 

The starter is made with a series of mounting holes to allow the actual starter to be indexed relative to the mounting flange.  I did have to rotate the starter one position from the location "as shipped", but that shift and the minor grinding were the only changes I needed to make.  I still need to verify proper depth of engagement with the flywheel.  Based on the catalog information, it should be close, but some adjustment may be needed (either shimming or grinding).  The starter does require a 12 volt system, however, that change was already part of my rebuild plan so it isn't any extra effort/expense for my project.

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