Yes, but some other modifications will have to be made. Front motor mounts will be different, and the water pump to radiator fit will be a problem. it's doable, but it's not a drop-in swap. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
"Front motor mounts will be different . . " The front motor mount should work (same part number)? Am I correct/wrong?
" . . the water pump to radiator fit will be a problem." If correct, what are possible solutions? I do not know about how/why the water pump fit will not work? What is the problem and what would be a solution?
It will depend on the production date of the 55 engine. 54 and early 55's will have the high mount water pump that aligns properly with the radiator to put the fan in the right position, same as the 216. Later 55's will have the low mount pump that causes problems with the fan position- - -low on the radiator and possible contact with the lower radiator hose. Even with a "short shaft" water pump that keeps the fan out of the radiator, a very small diameter fan that's too low on the radiator to cool well will be needed to keep the fan away from the lower hose. Dave's water pump relocation plate should solve both problems with the pump. Don't some of the front timing cover plates need to be drilled for a different front mount to bolt up correctly, or the plate needs to be swapped? Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
A 1940 flywheel is held on by 3/8” bolts and has a slightly larger center hole. 1942 on up used 7/16” bolts. I have seen 1940-41 flywheels drilled for 7/16” bolts, and the center hole diameter was not an issue, (even though it was designed to center the flywheel I am sure), as the three lineup dowels keep the flywheel in position.
My 1949 3600 came with a previously installed 261 to the SM420. Only noticeable alteration is where the previous owner hacked out the radiator mount sheet metal to move the radiator forward. Seems like there's plenty of room and in this day and age one would eliminate the fan and install an electric fan; solves the problem of space and noise. What we call a win-win!
You say its a '55 261 ... There were two series of trucks that year -- the last of the Advance Design and the first of the Task Force. The difference in the engines is significant in this case. Give us the casting number on your block. If the engine was built for the '55 1st series trucks, it will need far less modification to fit in place of a 216 (practically none -- if you use all your 216's peripherals. Use the 216 flywheel if you want to keep your 6 volt starter and the oh-so-cool foot starter pedal ... and who wouldn't?? ). If it is for the '55 Second Series (Task Force), then yes, you will have more work to do to make it fit.
I replaced a 216 in my '49 with an early 261 and had to make zero mods to make it fit. I used all peripherals (swapped out the timing gear backing plate to get the correct front motor mount), except the manifolds -- need the bigger Rochester carb to feed the bigger engine ... The good ole Carter W-1 is a great carburetor but it's nada bueno for the 261. I even used the 216's water pump without modification to either the block or the radiator. No need for electric fans, moving radiators, installing adapter plates, blah, blah, blah ... *if* you have the early series 261.
Don't do anything crazy until we figure out which block that is -- it could potentially save you a lot of time, effort and $$$
Here's my 261 installed. I used the 216 valve cover, too. Which, considering all the oil everywhere, may not have been the best decision...
~ John
A kid raised on Hotwheels, Matchbox and Tonka cannot be reasonably expected to own only one vehicle as an adult.
1949 Chevrolet 3804 In the Legacy Gallery | In the Gallery Forum 1973 IH 1310 Dump 1963 Kaiser M38A1 2001 International/AmTran RE3000 "Skoolie" 2014 Ford E-350 4x4 (Quigley)
I've figured out a way to duplicate those reinforcing brackets in steel, not brass, from a piece of square bar stock and mandrel-bending them to shape. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
