The inliners have lots of 261 info on their site including casting numbers to check your block with. The 54's are the desired blocks because they can be bored almost 1/4". The year is stamped on a pad next to the distributor-the first 2 digits should be the year but they are sometimes very faint. GMC's have the engine size stamped on the same pad next to the distributor-the first 3 digits are the CU (228/248/270/302)
261's were in the 54-62 chevy pickups and also in the GMC pickups until GMC came out with their v6 engine
That is not an accurate statement regarding the GMC's. Most, and maybe all, Canadian built GMC pickups had Chevy motors. There is some debate over whether any of them had GMC motors and I don't know the answer to that. A GMC of those years with a Chevy motor is either Canadian or the subject of a swap. The earliest US made GMC trucks and pickups had Oldsmobile or Pontiac inline sixes until the GMC 228 was introduced about 1940 (don't remember the exact year). Over the years that motor grew to the 248, 270 and 302. The 302 was also used in military applications starting pretty early. From the introduction of the 228 until 1955 US made GMC trucks came with GMC motors. When the V-8 era began in '55 the six cylinder equipped trucks still used GMC motors, but the V-8's were from other GM makes, mostly Pontiac. The GMC V-6 became the standard GMC motor in 1963. These days GMC trucks have Chevrolet motors.
Actually, if I remember correctly, the 261 was a "raised deck" version of the 235, meaning the block was cast taller to allow a longer stroke. TJ
Hey, I just "inherited" the old family '29 Chevy 1 1/2 ton truck. All original. Used to run good, but hasn't run in 12-15 years. Engine has been full to the top with oil for storage, farmer style. I think I'll drain it, fill it back up with diesel for a day or two and drain it again before I attempt to get it running. Any better ideas? Should I pull the head and re-gasket the top end first. Any opinions? TJ
No, the stroke is the same as a 235; in fact, both engines use the same crankshaft. The extra 26 cubic inches are the result of a 3/16 inch bore increase.
261's were used from '54-62 in the 60 series trucks and in '63 in some 4x4 trucks. Only the '59-63 USA made 261's had the full flow oiling. All were full pressure though. FYI, FULL PRESSURE DOES NOT MEAN THE SAME AS FULL FLOW... deck height is the same as a '53-62 235. Considering the options you have these days with either a shortened water pump or an adapter plate to use the older style pump, I can't see why a '54 is going to be the better choice, since it has byp*** filtration and you need to shim the bearings. I'll take the '59-63's... Canadian Pontiacs used Chevy 261's in some of their cars, but they were all hydraulic lifter and byp*** filtration.
I hope with a little work & time that they will be able to get that new Chevy V8 over 132hp. Time will tell
Why are the older water pumps better? I bought an older style water pump for my '53, then realized it's 235 was from a later car (has the later model water pump). Should I buy an adapter plate for my new pump instead of swapping and getting a later model pump?
The early water pump isn't BETTER than the later pump, it just makes retrofitting the engine into a '37-'53 car easier, since you don't have to shorten the pump, relocate the radiator, or buy a special pump to do it. Plus, if you're putting it in a '52-'53 car, the '54 motor mount bosses work without modification.
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