thought I’d write up a few lessons learned from the 224 to 235 engine swap project I just completed, just in case anyone else plans to do it. I had read all the tech articles and advice I could find installing a ’55-’62 235 in an earlier truck. These articles indicated that it was nearly a bolt-in operation. With that thought in mind I proceeded with the swap. I found that it was not quite as easy as I expected. Mostly because of my inexperience and that the articles are oriented towards late ’40 to early ’50s trucks. My 1940 Canadian GMC was a little different. My truck had the original 224, which is the Canadian cousin of the 216. The motors are almost identical except for a slightly larger bore and aluminum pistons instead of cast iron. I will not detail the entire process, but will highlight a few of the issues I encountered.
1. Water Pump - I found the so-called short shaft water pump did not work in my truck due to the lowered position of the fan. The fan hit the lower radiator outlet by about 2”. The fan would also strike the damper pulley. I also found that despite reports that the overall engine length is the same between a 235 and the earlier motor, it is not. With the short shaft water pump installed the overall length was about 1/2” longer. The solution was to use a 216 water pump adapter plate from Dave Folsum. This allowed use of a ’53-’54 216 water pump with 3/8 belt pulley. This required drilling and tapping 2 holes in the block, but was not hard to do. With this set up I used a repro 216-passenger car fan blade and a ’44 inch belt.
2. Radiator – I could find no reproduction of the 1940 GMC radiator so I took mine to an old time, local radiator shop. He had a custom core made for it, fixed any other leaks and converted the non-pressurized neck to accept a pressure cap. He warned me not to use a high-pressure cap due to the thinness of the tanks. I installed a 4 lb cap, which seems to be fine. The radiator normally mounts to the rear face of the radiator support. Even with the 216 water pump and adapter plate I needed to move the radiator to the front side of the mounting surface. This effectively moved the radiator forward about 1/2 inch. This gave me just over 1 inch clearance between the fan and radiator.
3. Flywheel – The 1940 flywheel could not be reused because it uses six 3/8” diameter bolts to attach it to the crankshaft. The 235 uses six 7/16” diameter bolts. I did not want to try to redrill these critical holes. Fortunately I got the correct 1941-1954, 10-3/4 flywheel with the 235 motor. I found that to properly time the motor the “triangle” mark on the flywheel indicates TDC, not the pressed in ball bearing that is discussed in the shop manual. This is what must be used when installing the distributor and for future timing checks.
4. Accelerator linkage – On the old motor, I carefully measured the distance from the rear engine face to the hole in the bellcrank for the accelerator rod. I then measured the same distance on the new motor and found the bellcrank hole was about 1 inch too far forward. I cut a wedge shaped piece out of the bellcrank and repositioned the part with the hole so it was 1-inch further rearward. I then welded it back together. This ensured that the truck’s accelerator rod would work with no other modification. It turned out great.
5. I used the old 224 valve cover with the stud adapter kit from Jim Carter. It worked fine and keeps the motor looking like the original.
Most everything else was straightforward. It took me about 4 months working on and off. I took my time and double-checked everything as I went because I was paranoid I would screw something up.
Hope this will help other in the future.
Steve
