Monday, November 7, 2016

History and Options of 1955 Chevrolet Tri-Five Carburetors Part, 1 "1955"

History and Options of 1955 Chevrolet Tri-Five Carburetors Part 1 "1955"


History of the Tri-Carburetor 1955

One of the most influential elements of the Tri-Five was the recent development of their newest 265 cid (4,340 cc) V8 engine, which was first offered in 1955. It was an overhead valve high compression, short stroke design that remained in production in various forms for decades. The base V8 had a two-barrel carburetor and was rated at 162 horsepower (121 kW), and the "Power Pack" option featured a four-barrel carburetor and other upgrades yielding 180 brake horsepower (130 kW). Later, a "Super Power Pack" option added high compression and a further 15 brake horsepower

In 1955 the 265 arrived on the scene with a 3.75-inch bore and 3.00-inch stroke (95.2 – 76.2 mm). It made 162 horsepower and 257 lb-ft in base form with a two-barrel carburetor. An optional Power Pack added a four-barrel carburetor (and other modifications) taking power up to 180 horsepower and an even 260 lb-ft of torque. When fitted to the Corvette, the 265 made 195 horsepower through a dual exhaust system. Later in the year Chevrolet added a Super Power Pack option to the Bel Air, taking it to Corvette power levels.

Six Cylinder Carburetor
Rochester Model “BC”

(1947-59) Rochester Model “BC” Carburetor, 6-Cylinder 235 CI Engine

The carburetor used on all six cylinder models is the Rochester Model “BC” down carburetor, equipped with an automatic choke.  This carburetor presented several distinct features of importance.

  1. Concentric fuel bowl-Regardless of any shift of fuel level in the bowl, the main metering jet is at all times immersed in fuel.
  2. Centrally located main discharge nozzle-a shift in fuel level has little or no effect on the rate of discharge from the nozzle.
  3. The main well and supported assembly, which contains the main metering jet and the power valve, is attached to the cover and suspended in the float bowl which provides ease in servicing.
  4. Automatic Choke-Insures proper starting and driving carburetion during cold weather operations.
  5. A fast idle mechanism, which is in linkage with the choke lever, is an aid to more efficient cold weather warm-up, insuring correct idle speeds during warm-up period.  

Rochester B BC BV Exploded View

Eight Cylinder Model Carburetor
Rochester 2GC

Rochester Model “2GC” Carburetor 8-Cylinder 265 CI Engine

The rochester Model 2GC two barrel carburetor was standard equipment on all 1955 Chevrolet's’ eight cylinder models.  While not interchangeable, the carburetors used on powerglide-equipped models and standard shift models are basically the same, and description and service operation are identical.  The carburetor incorporates the calibrated cluster design.

The cluster casting is the heart of the carburetor; it embodies the small or secondary venturi, the high speed passages, the main well tubes and nozzles, the idle tubes and the calibrated air bleeds for both the low and high speed metering systems, as well as the accelerating pump jets.

When the cluster is removed for service purposes, all of the vital parts can be readily seen, cleaned and examined; the main well tubes and idle tubes are permanently installed in the cluster body by means of precision pressed fit.

The cluster fit on a platform provided in the body casting of the carburetor so that the main well and idle tubes are suspended in the fuel.

A gasket is used between the cluster casting and the body platform.  This method of design and assembly serves to insulate the main well tubes and idle tubes from engine heat, thus reducing heat expansion and percolation spill-over during hot idle periods of operation and during the time the hot engine is not operating.

An external vent with a  protective cover to keep out dirt and other foreign matter is located in the center of the bowl cover to provide adequate venting  of the unit under all types of operating conditions.

The Model 2GC carburetor functions conventionally, using the standard six systems of carburetor: Float, Idle, Part Throttle, Poser, Pump and choke.  These systems are basically simple and easily be traced and understood.

The Model 2GC carburetor is of side bowl construction.  It is designed, however, with fuel supply jets and passages submerged enough below the liquid level to provide proper engine operation under all driving conditions.

Rochester 2GC Two-Jet Exploded View

Rochester carburetors were primarily used as original equipment carburetors on Chevy and GM cars and trucks. Rochester carburetor applications spanned the range of engine sizes offered by GM. The carburetors had multiple designs ranging from the Rochester Mono-jet carburetor, to the dual jet Rochester carburetor, to the most popular Rochester quadra-jet carburetor.

Over time, the Rochester carburetors evolved from basis mechanical units to carburetors that were electronically controlled by the vehicles on board computer systems.

The main difference between Rochester carburetors used on the various GM product lines that include Chevy, Oldsmobile, Buick, Pontiac Cadillac and GMC is the throttle linkage configuration. For the most part, the linkage differs by product line. Rochester truck carburetors are usually different from car carburetors even if the engine size is the same. Rochester carburetors have numbers identifying numbers stamped into the body of the carburetor. They are either a eight digit number that starts with "17XXXXXX" or a seven digit number that starts with "7XXXXXX". Look for the number on the body of the carburetor. The carburetor may have similar numbers stamped on the base or top, the number on the body will more accurately identify the carburetor.

A common issue on Rochester re-manufactured carburetors is wear on the throttle shafts that leads to either fuel or air leaks. This issue can be overcome by inserting bushings to that the play out of the throttle shafts creating a tight seal. This process requires special tapered drills. Always make sure that the bushings are being replaced when you buy a re-manufactured Rochester carburetor.

Eight Cylinder Model Carburetor
Carer WCFA

The basic 265 had a two-barrel carburetor and was rated at 165 H.P. Horsepower was increased to 185 with the addition of a four-barrel carburetor, and an underrated 195 HP version, called the "Power Pack" had a high lift solid lifter cam, high compression heads, and dual exhaust.

The Carter WCFB

The Carter WCFB Power Pack Caburator Option

A Carter WCFA carburetor was available as optional equipment on 8-cylinder engines.  This carburetor was used when higher engine performance wa desired.

The Carter Model WCFB carburetor was basically two dual carburetors contained in one assembly.  The section containing the metering rods, accelerating pump and choke is termed the primary side of the carburetor, the other section the secondary side. It has five conventional circuits as have been used in non optional carburetors for the 1955 model year.  They are:

2-Float Circuits
1-Low Speed Circuit
2-High Speed Circuits
1-Pump Circuit
1- Control (choke) Circuit.

The purpose of the float circuits is to maintain an adequate supply of fuel a the proper level in the bowls for use by the low speed, high speed, pump and choke circuits.  Primary and secondary bowls are separated by a partition.  The fuel line connection is on the primary side.  Fuel is supplied to the primary and secondary intake needles and the seats through a passage in the bowl cover. Located at the fuel inlet.  

The WCFB was Carter’s first attempt at a four-barrel carburetor. It was introduced in 1952. A total of 222 different WCFB models were made in the years 1952 through 1967. The WCFB was discontinued after the 1967 model year. I have seen a number of different meanings for the WCFB acronym. One employee of Carter once told me that it meant “wrought cast four barrel”; and used that terminology for years. However, a close friend who worked most of his life for Carter, chastised me for using this terminology. It seems the official Carter meaning was Will Carter Four Barrel (Will Carter of course being the inventor that started the Carter Carburetor Company). So I now use this designation when asked.
The WCFB is a “square-bore” carburetor; with three major castings: (A) throttle body (early aluminum, later cast iron); (B) bowl (zinc alloy) and (C) airhorn (aluminum).

While some of the WCFB carburetors had no air valve, most of the WCFB carburetors have the weighted air valve to prevent the secondary from flowing until the engine demand was sufficient to require flow from the secondary. There were also a very few WCFB units that had vacuum controlled secondary. These units, like the vacuum controlled AFB carburetors, were (and still are) exceptionally troublesome. Carter discontinued this design after a couple of years.

The Carter WCFB Power Packt Exploded View
While there are many categories of parts on the WCFB that look as if they should interchange; two in particular that give many enthusiasts problems are metering rods and floats. The metering rod is an extremely precision device. Most enthusiasts look only at the metering diameters; but do not realize that the LENGTH of the metering step is not the same for all rods. Carter utilized at least a dozen different step length profiles. When interchanging rods, unless one is deliberately changing the step length, one should compare the step length profile of the replacement to the original rod. The floats used in the WCFB are a double pontoon arrangement, connected by an arm. THERE ARE SEVERAL DIFFERENT FLOATS, WHICH APPEAR TO THE NOVICE AS IDENTICAL! Maximum buoyancy of a float occurs when the flat surface of the float arm is perpendicular to the fuel inlet needle. A method used by Carter (also Rochester in their 4G series, and Stromberg in most of their two barrel series) to adjust the fuel level was to move the height of the arm where the arm was soldered to the pontoons. Failure to observe this difference in floats may lead to carburetor flooding issues. Even if the float arm is bent to achieve the specified adjustment, the buoyancy change may cause a flooding issue.

There were actually two WCFBs used in the 55 model year, the earlier style is called the "bell-crank" style because it has a large bell-crank connected to the throttle linkage. I understand that it was used up through early February with the round snout air cleaner, then the second more common style was substituted, along with the oval snout air cleaner. My 55 was assembled in mid-February and I used the second style and oval snout, though it originally had a two-barrel carb set-up.

Carter Carburetor Company in St. Louis, MO was established in 1909, and ceased operation in 1985. It was founded by William Carter, who started experimenting with automotive carburetors while running a successful bicycle shop. His first, cast brass carburetor could meter and deliver fuel more accurately than many competing units. He sold Carter Carburetor Company 13 years after founding it to American Car and Foundry Company, a firm older than Carter himself. Carl Breer wrote that, upon learning that the Ball family (owners of Ball & Ball) was planning to leave the carburetor business, he set them up with Carter, which continued to produce the Ball & Ball basic designs, which were used by Chrysler.

Carter adapted carburetors for Willys Jeep four-cylinder engines, waterproofing them for water crossings and making it possible to keep the engine going even on a steep incline (the Y-S carburetor). Carter also produced the first American four-barrel carburetor, used for Buick’s 1952 straight-eight, and followed by the WCFB on the 1955 Chrysler C300. This was eventually superseded by the AFB and the AVS. The final Chrysler use of four-barrel Carter carburetors was the Thermo-Quad, which used a lightweight theroplastic float bowl, on the most powerful Chrysler engines.

Carter produced Rochester Quadrajet carburetors for their rival maker whenever demand outpaced Rochester's ability to make them. They were identical to Rochester's units except the Carter name was stamped into the body. In Carter's final years in the early 1980s, they also produced Weber carburetors under license, such as the three-barrel Type 40IDA sold as replacements (or fuel injection retrofits) for 1960s and 70s Porsche 911 S.

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