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The Forgotten 261 6 Cylinder Engine

Thursday, February 11th, 2010

Between 1954-1962, Chevrolet produced their famous full oil pressure 235 cubic inch six cylinder in trucks and it soon proved to be one of the greats among engines. However, at the same time a lesser known “big brother” to this base engine was being used. This was the quality built 261 cubic inch six cylinder! The 261 was available in 2 ton (5000 or 6000 series) trucks and school buses. During it’s early years (1954-1957) it was an extra cost option above the standard 235 six cylinder.

In 1958-6192 (the 261 now had a full flow remote oil filter) it became standard in the 2 ton chassis up to 19,000 pounds gross weight. Above that Chevrolet substituted a V-8.

This larger six was not offered in US cars, however there was an exception in Canadian built full size Pontiacs. Their base engine, also produced only in Canada, was the 261 not the V-8 as in the US. This provided basic power, great dependability, and better gas mileage.

Basically, this larger engine was a 235 with the same crankshaft but GM engineers made various modifications to give it extra strength and horsepower. It’s standard bore diameter increased from 3-9/16 inches to 3-3/4 inches. The connecting rods were heavier and attached to increased diameter piston wrist pins.

Its higher lift cam shaft, for better breathing, was shared only with the early 235 six cylinder Corvette. A modified larger Rochester carburetor was also a 261 only feature. Unfortunately most of these larger sixes have long since had their original Rochesters replaced with 235’s and therefore do not perform to their full potential.

In pure big truck form the 261 has a larger thermostat housing holding a double acting thermostat. This is designed to circulate water through the block and head before the thermostat opens to allow hot water into the radiator. Thus, no internal steam hot spots during warm ups, especially in winter. This is particularly important with very cold coolant. Vital engine spots can become very hot before the total coolant becomes hot enough to open a normal thermostat on the front of the block.

 

261 engine 1

 

6 Cylinder Engines Jobmaster Thriftmaster
Displacement 261 Cu.In. 235.5 Cu. In.
Bore 3 3/4″ 3 9/16″
Stroke 3 15/16″ 3 15/16″
Firing Order 1-5-3-6-2-4 1-5-3-6-2-4
Compression Ratio 7.8 to 1 8 to 1
Horsepower 33.7 (AMA) 148 (Rated) 30.4 (AMA) 140 (Rated)
No.of Main Bearings 4 4
Wrist Pin Diameter .927 inches .875 inches
Rod Shaft Thickness Front to Back .595 inches .595 inches
Rod Shaft Thickness Side to Side .975 inches .760 inches
Crankshaft Journel Diameter 2.435 2.435
Engine Color in trucks Green -some later Yellow Gray

 

The block and head surface have three pair of matching small “steam holes” that allow any steam hot pockets to vent away from the open water cooled areas between the cylinders that are not solid metal. Of course, this means the 261 must have its own specialized head gasket.

261 engine 2

 

After four years into production, the major quality feature was added to the 261 engine. For the first time a Chevrolet inline six cylinder came standard with a full flow oil filter system. This improvement, used only with the later 261, forced oil through a remote filter cartridge before it reached the engine. It was not like the optional by-pass oil filter system as found on 216 and 235 Chevrolet sixes. This extra helped insure longer life to this larger six cylinder that was often subjected to heavy commercial use.

A full flow oil system has been a characteristic of almost all automotive engines for over 40 years but it was just beginning in the mid 1950’s. With the 261, the disposable filter is remote and not built in as with later engines. It still resulted in a major design improvement.

As with the 235 light truck engine, the 261 came standard with solid valve lifters and an aluminum camshaft timing gear. The passenger car’s 235 was equipped with hydraulic valve lifters and a fiber timing gear for quieter operation.

During the 1955-1962 Canadian Pontiac application the lifters were the hydraulic type, the cam gear was fiber not aluminum, and it did not have the full flow oil filter. These Canadian made 261’s did not add the full flow filter in 1958 as in the U.S.

Visually the 261 looks almost identical to the 235. It perfectly replaces the smaller engine and in stock condition increases horsepower from 140 to 148.

Those planning on a major rebuild or adding performance options to their Chevrolet inline six should seriously consider locating a 261. Often there is no extra cost in purchasing a re-buildable unit, and the results will be rewarding. If you plan on adding additional carburetion, a higher lift cam, or just want additional performance and more lower end strength in your daily driver, the 261 is for you!

Locating and Identifying a 261

Though last placed in larger Chevrolet trucks almost 40 years ago, this now scarce engine can still be located and often at a price no higher than for the smaller 235. Many still remain in the original Chevrolet trucks and are now setting in salvage yards or behind farm buildings. In Canada, the big Pontiac cars are sometimes in the back rows of more isolated older wrecking yards.

Don’t overlook the wrecked and badly rusted Chevrolet cars of the 1940’s and 1950’s, particularly those showing signs of some past exterior customizing changes. The Chevrolet enthusiasts of that era knew about the 261 and its potential for added performance. Some of these will already have had extras added such as a higher lift cam shaft, extra carburetion, or dual exhausts.

When you have found what you suspect might be a 261, check a few specifies to verify you have the real thing and not the visual almost identical 235. Casting numbers, not stamped numbers, on the 261 head are very visible beside the rocker arm cover. A different set of numbers relate to the 261 block. These seven digits are located on the right side between the fuel pump and starter except for 1954 where it is located forward of the fuel pump. See chart below.

YEAR ENGINE SIZE BLOCK NUMBER HEAD NUMBER
54-55 261 3703414 3733950 3703570 3836850
55-57 261 3733340 3837012 3703570 3836850
58-62 261 3739365 3769717 3769925 3836850

 

Watch for the “Captain’s Bars!” The 261 has two pairs of parallel raised 3/4 inch long bars cast in the block. This is not seen on a 235 except 1954. One pair is above the starter and the second pair is at the top middle of the left side of the block very close to the head. See photos below. The one exception is the early 261 produced in 1954 to mid 1955. It has only one “Captain Bar” above the starter but keeps the pair on the left side.

261 engine 3

261 engine 4

261 engine 5

261 engine 6

 

Most used 261 blocks are rebuildable, however often their cylinder heads will have a few very small cracks in the combustion chamber. This is typical due to occasional abuse of over heating in past years. If you choose not to add to your expense by having the cracks repaired, an alternative exists. The more common 235 head is the same except for the three pair of internal steam holes. These can be manually drilled to make the water flow just like in the 261! Sorry, but some 235 heads can be cracked even more than the 261 because they lack heat releasing steam holes.

“Warning” When Installing a 261!

The stock remote filter system has two very visible 3/4″ lines threaded into the block. One is from the pump to the filter and the other from the filter back to the block. Oil must leave and return to the engine by these lines (even if the filter is eliminated) or the engine will fail from lack of lubricant. Many 261 engines have been quickly seized after persons plugged the two oil line holes. They had many years experience on Chevrolet engines without the full flow oil system. Some thought it was an easy fix to just remove the 3/4″ lines if one was leaking and cap the holes. This procedure was acceptable on the older 216 and 235 but never on the 1958-1962 261 truck engine.

Buy Parts for 1947 to 1955 Trucks

 

1936 – 1946 Engine Dust Pans…Pure GM

Thursday, February 11th, 2010

During the 1930’s and 1940’s our Nations roads were dirt and gravel. Paving had been underway for many years but there was still a long way to go.

To protect engine componants from a constant attack of dirt, GM designed metal stamped panels that attached to an area where the engine block and oil pan connect. This slowed dust from collecting on moving parts and for certain around the engine air breather.

1936 1946 engine dust pan 1936 1946 engine dust pan 1936 1946 engine dust pan 1936 1946 engine dust pan
1936
1936 ?
1937- 1938
1939-1946

Over the years, these gradually fell from their attaching fasteners and found their way to the roads. Potholes and ruts were often the culprits. The vehicle owners and even hired mechanics tended to remove them during maintenance. They were rarely paced back into position.

Today finding a pair of these engine dust pans is almost impossible. Newer generations have no knowledge of their existance. These photos of the different years should be about 1936 and 1946.

If someone is in disagreement on the years, email us at info@jimcartertruckparts.com

Engine Paint

Thursday, February 11th, 2010

The following article used by permission of the writer: Robert Hensel, Technical Advisor Coordinator for the Vintage Chevrolet Club of America. Bob can be contacted by email: cacres@charter.net

I do not know of any book that gives the engine colors for all Chevrolets. I have found it here and there in many Chevrolet letters and books. I have come up with a list that covers most engines and some speculation, that does not mean that Chevrolet always followed what they said either.

The color of the fan is another sometimes sticky problem. As best as I know all replacement fans were black, we have some controversy in the early 30’s. Some pictures show the fan was pained engine color at the time of production. In the Vintage Chevrolet Club of America we do accept black and in my opinion black is what they should be. I think the engine for production was assembled and painted before the fan and other add-ons were added to the engine before it was put into the vehicle. The oil fill/breather tube is another case of engine color or black. I go with black.

Maybe this would be an idea for an article and maybe start some arguments. What we strive for in the VCCA is what the vehicle was like when new and offered to the public using only genuine Chevrolet parts available at the time of production. A good example that can cause hard feelings is white walls. They might have been available but Chevrolet did not offer them until the mid 30’s and I don’t think it was until 1962 or ’63 that you could order them on a truck. The dealer could install them but Chevrolet did not offer them, they would be after market items.

At times it is fun trying to find answers to the question but it can get frustrating when the answers are not to be found. I have a very large Chevrolet literature collection, and trucks are my main interest, but I can not always find the answers.

The vehicle listing from a 1923 Parts Price book does not cover the 1912 and 1913 Chevrolets, it does not list the T Truck for 1918 but they were built starting late 1917. The G series truck was Chevrolet’s first attempt at what we call a 3/4 ton truck. It was only built in 1921 and 1922. One more interesting thing in the list is the M series of vehicles of which there is a light delivery chassis listed. This was the ill fated copper cooled engine and only a very few cars were built before they were called back. There are at least two examples, both coupes that still exist and I know of at least one engine. As best as I know they never built any of the light delivery chassis for sale. What happened to the vehicles that were called back is still a mystery to me. I have heard they were dumped in Lake Michigan, or the were converted to water cooled cars. I heard they used the left over engines in lift trucks used in the plants in the late 20’s and early 30’s but never found any proof of this. The conversion idea sounds most logical. About the only exterior differences was the shell in place of the radiator. It had many horizontal louvers in it. The idea here is the 1 ton truck used the same engine as the light delivery starting in 1923. Before that the Light Delivery and the G truck used the 490 engine and the T used the F series engine that had a longer stroke.

Engine Colors

YEAR
ENGINE
COLOR
1912-1914 6 Cylinder Black*
1914-1923 4 Cylinder Gray
1924-1928 4 Cylinder Dark Green (gray green)
1929-1936 209 CID Blue Gray
1937-1953 216 CID Blue Gray
1941-1952 235 CID Blue Gray
1953 Truck 216 Blue Gray
1953 Standard Shift 235 Blue Gray
1953 Power Glide Blue
1953 Truck 235 Blue Gray
1954 Passenger Blue
1954 Truck 235 Gray
1954 Truck 261 Green
1955 Passenger 235 Gray
1955 Passenger V8 Orange
1955 Truck Thriftmaster 235 Gray
1955 Truck Loadmaster 235 Green
1955 Forward Control Loadmaster Gray
1955 Truck Jobmaster 261 Yellow/Green
1955 Truck Taskmaster 265 Yellow
1955 Truck Trademaster Gray
1956 Passenger 235 Blue*
1956 Passenger 265 Red
1956 Passenger V8 Orange*
1956 Thriftmaster 235 Green**
1956 Thriftmaster Special 235 Gray**
1956 Jobmaster 261 Yellow**
1956 Trademaster 265 Gray**
1956 Taskmaster Yellow**
1956 Loadmaster 322 Red
1957 Passenger 322 Blue**
1957 Passenger 265 V8 Chartreuse
1957 Passenger 283 V8 Red
1957 Truck 235 Green**
1957 Truck 261 Yellow**
1957 Truck 265 Gray** Different Options
1957 Truck 283 Gray-Yellow-Green-Black-Orange
1957 Truck 322 Red
1958 Passenger 235 Blue*
1958 Passenger 283 Orange*
1958 Passenger 348 Orange
1958 Truck 235 Gray***
1958 Truck 261 Green
1958 Truck 283 Light Duty Gray***
1958 Truck 283 Light Duty Green***
1958 Truck 322 Orange-Red
1958 Truck 348 Tan-Gray
1959 Passenger 235 Blue*
1959 Passenger 283 Orange*
1959 Passenger 348 Orange
1959 Truck 235 Gray
1959 Truck 261 Green
1959 Truck 283 Light Duty Gray
1959 Truck 283 Heavy Duty Green
1959 Truck 322 Orange-Red
1959 Truck 348 Orange
1960 Corvair Natural*
1960 Passenger 235 Blue*
1960 Passenger 283 orange*
1960 Passenger 384 Orange
1960 Truck 235 Blue Gray
1960 Truck 261 Green
1960 Truck 283 Trademaster Green
1960 Truck 283 Taskmaster Gray
1960 Truck 348 Gray
1961 Corvair Natural*
1961 Passenger 235 Blue*
1961 Passenger 283 Orange*
1961 Passenger 348 Orange
1961 Covair Truck Natural*
1961 Truck 235 Blue Gray***
1961 Truck 261 Green**
1961 Truck 283 Gray**
1961 Truck 348 Gray**
1962 Passenger 153 Orange
1962 Passenger 194 Orange
1962 Covair Natural*
1962 Passenger 235 Blue*
1962 Passenger 283 Orange
1962 Passenger 327 Orange
1962 Passenger 309 Orange
1962 Covair Truck Natural*
1962 Truck 235 Blue Gray**
1962 Truck 261 Green**
1962 Truck 283 Gray**
1962 Truck 327 Green
1962 Truck 348 Gray**
1962 Truck 409 Orange
1962 Diesel 212 Green
1962 Diesel 318 Green
1963 Passenger 153 Orange
1963 Passenger 194 Orange
1963 Covair Natural*
1963 Passenger 230 Orange
1963 Passenger 283 Orange*
1963 Passenger 327 Orange
1963 Passenger 409 Orange
1963 Covair Truck Natural*
1963 Truck 153 Gray-Orange*
1963 Truck 230 Gray-Orange*
1963 Truck 235 Blue/Gray**
1963 Truck 261 Green**
1963 Truck 283 Gray**
1963 Truck 292 Green
1963 Truck 327 Orange/Red
1963 Truck 348 Gray**
1963 Truck 409 Orange
1963 Diesel 212 Green
1963 Diesel 318 Green
1964 Passenger 153 Orange
1964 Passenger 194 Orange
1964 Covair Natural*
1964 Passenger 230 Orange
1964 Passenger 283 Orange*
1964 Passenger 327 Orange
1964 Passenger 409 Orange
1964 Covair Truck Natural*
1964 Truck 153 Orange
1964 Truck 230 Orange
1964 Truck 283 Orange*
1964 Truck 292 Green-Black-Gray*
1964 Truck 327 Orange
1964 Truck 348 Tan/Gray, Orange
1964 Truck 409 Gray
1964 Diesel 212 Green
1965 Passenger 153 Orange
1965 Covair Natural*
1965 Passenger 194 Orange
1965 Passenger 230 Orange
1965 Passenger 283 Orange
1965 Passenger 327 Orange
1965 Passenger 396 Orange
1965 Passenger 409 Orange
1965 Covair Truck Natural*
1965 Truck 153 Gray
1965 Truck 230 Blue
1965 Truck 250 Blue/Grat
1965 Truck 292 Green-Dark/Gray
1965 Truck 327 Green
1965 Truck 348 Gray
1965 Truck 409 Gray w/silver rocker cover
1965 Diesel 159 Green
1965 Diesel 212 Green
1965 Diesel 318 Green
1965 Diesel 351 Green
1965 Diesel 477 Green
1966 Passenger 230 Orange
1966 Passenger 250 Blue
1966 Passenger 283 Orange
1966 Passenger 327 Orange
1966 Passenger 396 Orange
1966 Passenger 427 Orange
1966 Truck 153 Gray
1966 Truck 230 Blue
1966 Truck 283 Blue/Gray
1966 Truck 292 Green-Dark/Gray
1966 Truck 327 Green- (Blue Suburban)
1966 Truck 348 Gray
1966 Truck 409 Gray
1966 truck 194 Gray/Blue

* Assumption

** Assumption because it is a carry-over from a previous year.

*** Assumption because it was found in next years book.

Disclaimer: Due to the fact that there is no official book that lists all the Chevrolets engine colors, many of these colors are assumption. Many of the colors in this list are taken from authenticated vehicles. Various assembly plants had different colors and tints. Colors were also subject to availability and these may have changed at the plant. Also different options on a vehicle would determine the color of the engine especially the truck 283 engine. Also remember the primary goal of the assembly plant was to get the vehicle out to the consumer. If a color was used up, the next available color was utilized.

Note: When Orange is stated, it means Chevrolet Orange.

Special Thanks to: Gale Garmon of K-ville, PA for assisting in determining engine colors.

A Tip from Carl Pearson: 292 Green can be obtained through Krylon, paint #2013, known as GM Alpine Green or Detroit Diesel Green.

More on GM engines

T-1918 – ’28 Light Truck has the same engine as the 4-cylinder car engine.

1941 – 235 CI engine was available in 1 1/2 ton and COE models.

Through the 1950’s – GMC also produced a 302CI 6-cylinder engine.

1957 – GMC produced a 347 CI Pontiac engine