The Stovebolt Site Forums The Shop Area Engine Shop 261/235 interchange

I was wondering if the accessories, such as the fuel & water pumps are interchangable between 235's & 261's.

Also, then, are the only unique parts on a 261 the connecting rods and the head gasket.

Thanks...Tom.

The head is differant on the 261 but you can use a 235 head if you drill the steam holes. The water pump isn't the same, but I think the fuel pump is.

I don't know about 235 vs 261 differences for all years ('54-'62) but here are differences between Thriftmaster 235 and Jobmaster 261 engines (for 5000 and 6000 series trucks) in 1954:

- camshaft
- carburetor (for 6000 series is different)
- PCV on 6000 series
- block (obviously), head, and head gasket (6 more water holes on the 261)
- pistons, piston pins, connecting rods
- 235 Loadmaster valves in the 261
- valve springs
- valve rocker arms. push rods, rocker shaft (wall thickness)
- valve tappet (lifters)
- fan (increased pitch on the 261)
- water pump and hoses are 1/4" larger inside diameter on 261
- thermostat and housing
- engine (distributor ignition) timing (flywheel marks)

Some of the differences above refer to parts that might be interchangeable but they are not identical. Most of the valve train parts, for example, are "unique" to the 261 but the valve train parts might be interchangeable (same dimensions) between 235 and 261. The beefed-up valve train was designed to handle the higher lift of the 261 cam.

The Loadmaster 235 was optional on 4000 series trucks and it had a few of the features of the 261 (that the Thriftmaster did not have).

This information is from the 1954 Chevrolet Truck Engineering Features manual.

The '58-'62 261 has a full-flow (not bypass) oil filtration option. The 235 never had a full-flow oil filtration option.

Tim

As you say the individual parts are all the same difference lol.With the exception of the pistons, every part is interchangable. Like the posts above state, they may require modification.Besides the steam holes on a 261 head(#850) the 261 head supposedly has larger combustion chambers.My observation is ,GM lowered the compression by lowering the piston height at TDC.Perhaps someone has actually CC'd the combustion chambers?The #848 head is the only 235 replacment offered by GM in later years, but I have seen a few other casting numbers on 55-56 engines. 261 rods fit properly on a 235 crank, but the wrist pin holes are larger ,so custom pistons are required.The crank shafts have the same part number as do the valve springs, but 261's use rotaters on the exhaust valves.The water pump impellers and bolt pattern are identical but the castings have different fittings and so on. The intake on engines with governors is a lower profile .My old GM parts books list the same part numbers for most every thing except the differences mentioned. Original manafacturer replacement parts are often standarized more than the original stuff to lower dealer inventory costs.

That's the info I was looking for. The 261 motor I have is complete, but the carb & water pump are shot. I bought a carb at a swap meet this weekend, but I guess I need to talk to the folks at Langdons Stovebolt or Patricks before I dig into this any further. Thanks. Tom