Jim Carter's Old Chevy Trucks - Classic Chevy & GMC Truck Parts for all of your restoration needs! 1000's of parts in stocks now!

Mechanical

The First Chevrolet V-8 Full Pressure Oil Filter

Wednesday, February 14th, 2018

The enclosed page from the Chevrolet Factory Assembly Manual is dated July 23, 1955. It appears to be announcing the new full flow oil filter that attaches to the lower left rear side of the 265 V-8 engine block.

For the early 1955 year- after the introduction of their first small block V-8 – the oil filter had been a dealer installed by-pass unit attached to the front of the intake manifold. See tech article under 1955-66, then click on accessories.

As per the attached drawing, this new mid 1955 filter was not a spin-on design. The cartridge was inside a round housing that Chevrolet calls an “oil filter assembly”.  One long center bolt was removed to replace the inner throw-away cartridge.  This system was used on Chevrolet small block V-8 s for about 10 years while some other vehicle manufacturers used the spin-on filter as used today.

Chevy V-8 Engine Instruction

Early V-8 Draft Tube

Sunday, February 11th, 2018

Surprise to many, the first Chevrolet V-8’s had a lower end draft tube just like the six cylinders of the same years.  The V-8’s are hidden between the distributor and the firewall and not in easy view.

The Chevrolet parts catalog for 1957 shows this “tube assembly” number 3726641 available by the dealer from 1955 through 1957.

From almost the beginning of the internal combustion engine, some type of venting of the lower crank case was needed. It was not until the early 1960’s that many vehicle engines were designed to pull the vapor from below the piston rings to be burned in the engines combustion chamber. Thus, much air pollution was eliminated particularly from well-worn engines, often referred to as lower end blow-by.

V-8-Engine-Instruction

1954-62 Chevrolet 235 Power Glide Hydraulic Valve Lifters

Tuesday, January 30th, 2018

Very Important Cam Shaft and Valve Data

Occasionally when purchasing a used 235 high oil pressure engine, it may have been originally in a Chevy car with a Power Glide transmission. This will have a different cam shaft due to the Power Glide engine having hydraulic lifters. The lobes on the cam shaft must be a different height because of the lifters. In fact, hydraulic and solid lifters cannot be interchanged with non-related cam shafts!

To be absolutely sure if your 235 engine was originally from a Power Glide car do the following:

1. Remove the short side plate on the right side of the block.
2. Remove valve cover.
3. Loosen a rocker arm enough so one push rod can be removed.
4. Raise a valve lifter out of its resting place.
5. Place your finger in the valve lifter hole you have just created and feel for a
3/8” diameter hole on either side. Holes allow motor oil to lubricate and fill
the hydraulic valve lifter.

Engines with factory solid lifters will not have these 3/8” holes.

FYI: You can place a set of truck solid lifters with matching cam shaft in a 235 that originally came with hydraulic lifters. However, the reverse will never work! Without the 3/8” holes beside the hydraulics the lifters will not oil.

Chevrolet V-8 By-Pass Oil Filter

Tuesday, January 30th, 2018

Its 1955 and Chevrolet trucks and cars offer their first small block V-8, a light weight with 265 cubic inches. (Not counting their short lived V-8 in 1917-18).

This series of V-8’s, along with the high pressure inline 235 six cylinder (1954-62), are probably the most successful engines in the General Motor’s history up to that time. With proper maintenance they were long lasting and repairs were possible even by medium skilled “shade tree” mechanics.

As with their 235 six cylinders through 1962, the first V-8 did not come with an oil filter. It was a Chevrolet dealer accessory. Adding an oil filter was usually done by the dealer from a GM kit. There was no place on the side of the engine block to receive a filter! To create this V-8 filter assembly the Chevrolet Division used a canister from a 235 six cylinder and welded a right angle lip on the bottom. Here, this unit was secured under the thermostat housing on top of the intake manifold. Quite unique!

The big change was in 1956.

It was this second year of the 265 V-8 that GM added a position in the engine block casting for the oil filter on the lower side. This was not a spin-on filter but was in a canister held to the block by a large center bolt. Now for the first time the new truck or car had a factory installed “full flow” oil filter like vehicles today. Motor oil goes through the filter before it reaches the engine!

test
Accessory Oil Filter Installed

test
Oil fill pipe on side of canister

test
Close up. Lip under water outlet

test

test
265 V-8 without option oil filter

Valve Cover Trivia

Tuesday, January 30th, 2018

If you really like learning about old Chevy truck six cylinder history, this article is for you.

We recently visited Jerry’s Chevy Restorations in Independence, Missouri and noticed an interesting display on a side wall of his shop. Jerry has the complete series of Chevrolet “Stovebolt” six cylinder valve covers used on cars and trucks between 1937 and 1962. This 25 year display is even painted the correct gray color for trucks.

test

No doubt it took much time cleaning, repairing, and painting to make them ready for their place in his restoration shop. Here is the order they were used in Chevrolet vehicles.

1937-38

test

test

The two mounting stud grommets fit in a pocket below the surface of the cover. The valve cover must be removed to replace them. See the backside where the small metal strip secures the rubber grommet. (Not on 1940 and newer) Three necessary venting slots are on the top to allow the engine to breathe.

1939-48

test

Redesigned with two larger attaching holes in cover so it is not removed to replace the mounting stud grommets.

1949-53

test

test

New Idea: For the first time the add-oil hole is on the top of the valve cover. Now the mechanic did not add oil through the side engine draft tube. Good change! Less chance of some oil spilling as the oil container was placed down to the draft tube on the side of engine.

1949-53 – COE Trucks

test

test

This different valve cover is used on the cab-over-engine “COE” trucks. Because the engine is under the cab, oil cannot be added through the top of the valve cover as with a conventional cab. Therefore, add oil hole is not punched but the spot remains where it is placed in a conventional cab of the same years. GM wanted no part of a gradual oil leak from a capped hole and it being so difficult to reach. The continual oil seeping would not be good for the truck owner or repeat new COE sales.

NOTE: The Chevrolet Master Parts Catalog for April 1, 1950 shows the buyer of a COE valve cover must purchase one for a conventional cab. The manual states it will be necessary to seal the oil filter hole with a thin sheet metal disc to provide clearance. Therefore, the photo in this article is of a pure factory GMC valve cover, not a modified unit altered by a dealer.

Of course, the Chevrolet Motor Division knew the chance of a protected valve cover under the COE cab would probably never need replacing. This pure COE valve cover was probably never not available!

1954-Early 55

The new high oil pressure 235 engine is introduced in trucks! Oil cap continues to be sealed as 4 small breathing slots are in a different position and are front to back on the top. This gives a place for the Chevrolet script lettering to be stamped on top. Good advertising.

Now, instead of 2 vertical studs with nuts for keeping the cover attached to the engine head, an overdue improvement is introduced. Four short machine screws press directly down on the new perimeter lip surrounding the valve cover. This presses on the valve cover gasket and stops oil leaks that occurred on the earlier design when the two studs were over tightened.

test

test

Late 1955-57

More technology! To stop engines from sometimes leaking oil out of the 4 breathing holes on top of the cover they were removed! Breathing now occurred through a redesigned add-oil cap. It was used through the end of the series in 1962.

test

test

1958-62

The add-oil cap is moved from the front to the middle. Because this 235 engine is tapered in its mounts to the rear and the new 1958 cars have a lower hood, GM moved it. This gave just a little more space and prevented hood contact with the oil cap.

NOTE: Because of the new center location of the add-oil hole, the Chevrolet script must be “half the size” on the valve cover top.

test

test

1955-59 1/2 Ton NAPCO Springs

Monday, October 3rd, 2016

Buy Chevy & GMC Truck Parts only @ Jim Carter's Old Chevy Trucks. 1000's in stock now!
If you have a NAPCO 4 wheel drive ½ ton, the following might be of interest. Owners sometimes wonder if their NAPCO 4 x 4 was installed at a franchise NAPCO shop that were in most medium size towns or was it installed on a Chevrolet GMC factory assembly line when GM began offering them in 1957. (NOTE: GM first offered 4 wheel drive trucks in 1957 and used the pre-existing NAPCO system) Of course, the letters NAPCO were never printed in GM literature and the NAPCO fender emblems were not attached as they would be by a franchised dealer.

If you have a 1957-59 Chevrolet or GMC, you can always tell if it is a NAPCO system by looking at the front of the axle housing. The N-A-P-C-O letters will be in full view!

Another quick way to tell the source is the leaf springs. From a NAPCO installed kit the ½ ton front springs are not changed but have 6 leaves on the front. The GM assembly line used 7 leaves. On the rear NAPCO installed kit they used the original 7 leaves. GM used an 8 leaf spring.

test

Engine Vacuum Leaks

Thursday, June 4th, 2015


Even the smallest vacuum leak on an internal combustion engine can prevent it operating to the level of its capability.

No matter how well you rebuild the carburetor, adjust the timing, or clean the gas tank, the engine will continue to operate below what it should even with a small vacuum leak.

On older engines a quick, easy way to check for leaks near the cast iron manifold will often uncover the problem.

    1. Place a large piece of cardboard behind the radiator cooling fan. See photo. This stops fan air flow in the area of the meeting point of the manifold, carburetor and engine head.1
    2. Use a spray can of starting fluid (available at auto parts stores). Let engine idle, and lightly spray in areas of where air flow will let into the carburetor through.2
    3. If you have even a small vacuum leak the starting fluid will be pulled incorrectly into the engine combustion chamber. The engine RPM will instantly increase. Your engine problem has been found! A new gasket or insulator plate will usually make all well.3

Short Shaft Water Pump Discussion

Monday, March 17th, 2014


The revised Chevrolet 235 and 261 high pressure inline six cylinder engine (1955 through 1962) was given a much better cooling system than prior years. This was due to a big change in the water pump and how it attached the front of the engine block.
The prior 216 and early 235 design pulled coolant out of the engine block through two quarter size holes, into an exterior pump, then forced it through the lower radiator hose and back into the engine block. This system worked well for millions of Chevrolet cars and trucks for at least 16 years.
One of the difficulties began to develop as these vehicles became older and were exposed to faster speeds of more modern roads and radiator coolant water contained a high calcium content.
Calcium started to slowly accumulate inside the block but even more in the radiator cooling tubes. The coolant temperature would rise in the block due to slower water circulation.
This was first noticed in the low geared 1 ½ and 2 tons, even with their extra row of radiator cooling tubes. Local radiator shops would remove the top radiator tank and “rod out” the cooling tubes to restore most of the original radiators ability.
With the introduction of 2 new Chevy six cylinder in 1955, General Motors made a change in the water pump that would at least postpone this over-heating problem for many more years than the earlier engines.
Now, the water pump propeller actually was inside a 4” hole in the front of the block. It could move a higher volume of coolant through the block. Chevrolet cars and trucks could now be used so many more miles before this rodding of the tubes was necessary.
With General Motors wisdom, they designed their new high pressure 235 and 261 engine to easily fit in the place of a failing earlier 216 engine. The main problem with this engine exchange was the longer length of the new water pump shaft.
Local mechanics would then either cut some metal from the upper and lower air dam to move this radiator forward a few inches or shorten the pump shaft to provide radiator clearance for the fan on a new 7” pulley.

The word spread quickly that the shaft could be cut and the 4” diameter pulley from a 1953-1954 would press in the proper position. (Most shops could find one of these pulleys on a nearby used engine)
All fit well but the rotating RPM speed of this small 4” pulley turned the fan and pump 20% faster at the same vehicle speed. Because of the low engine gearing of the larger 1 ½ – 2 ton trucks we have heard owners feel their water pump experienced “cavitation” (the fan is turning so fast water flow will almost come to a stop). It may not boil the coolant but it just might! At slower road speeds the water temperature returns close to normal. A small 18” fan from an early 216 donor engine was also required to prevent contacting the lower radiator tank.

NOW enters another modified water pump that has a much flatter 7” diameter pulley. This lowers the fan speed to the correct RPM that GM intended to be used on ½ ton up to the 2 tons. It was a one size fits all!
It is the other short shaft pump design! You can easily install this modified 235 and 261 engine in the 1953 and older truck (and cars). It is strongly recommended that you use this pulley pump for Chevy trucks rated over ½ tons!
It requires the correct wider four blade 235 fan, however the blades must be bent slightly forward to miss the lower radiator tank.

Therefore, if you want to operate your 235 and 261 engines water pump at a slower speed as GM intended, the 7 inch pulley design is the way to proceed. It will cool ¾ to 2 tons with lower differential gearing at high speeds with no boiling, just as the vehicles were designed. Yes, Jim Carter Truck Parts has the new updated pump assemblies available at a price of $159.00 (a used original wide blade fan is by another order).
A small 4 inch diameter pulley water pump have been placed on a 235 or 261 engine since they were first introduced. They usually work well with vehicles with clean radiators on cars and ½ ton light vehicles that have been given a higher speed differential. Not recommended for larger trucks as water temperature will raise at higher speeds! We have these that operate well (without add-on air conditioning) at our company at $130.00.
As the owner of Jim Carters Truck Parts, I can assure you we have sold over 500 short shaft water pumps with 4 inch pulleys in the last 10 years. Return rate is about 4%. I suspect it is rarely due to an inefficient pump but rather the new customer not aware of the difference between a 216 and later 235 six cylinder. Maybe a few were using them on a low differential ratio ¾ to 2 ton truck.
Does the 4 inch pulley cool as well as the 7 inch design? Probably not on larger trucks! In some situations, if your radiator has calcium build-up, the coolant flow can be so restricted, your temperature gauge will show an increase at highway speeds. The 4 inch pulley turns the water pump much faster than GM intended!
With the low differential gearing (as in the ¾ ton to a 2 ton) plus driving higher speeds, the increase engine RPM will definitely cause temperature increase. It can go so far at very high speeds causing the water to cavitate and the coolant circulation will almost come to a stop! It may not boil the coolant but it just might!

testtest
4 inch pulley

testtest
7 inch pulley

1955-59 GMC Front Motor Mount

Friday, January 24th, 2014

1937 Chevrolet Lower Bar
1937 Chevrolet Lower Bar

 

1960-66 GMC V-12 Engine

Monday, July 2nd, 2012


1960-66 GMC V-12 Engine

Forgotten by most is the gasoline V-12 engine made by the GMC Division of General Motors in the mid 1960’s. This very large one piece engine block was made for GMC’s largest trucks. Examples of these vehicles were water carrying fire truck, and off road vehicles such as quarry trucks which hauled tons of rock. As can be imagined, the pulling power of these trucks must have been at the top for GMC’s fleet.

Unfortunately, due to the weight of the truck and engine, most were sold to metal recyclers when their working days were over. Most of the few remaining V-12 engines are in fire trucks that have been used only during fires or fire training.

The attached photos show a ½ ton 1964 GMC with one of these V-12’s made to fit for display at shows. Owner unknown. What a mechanical project to fit it into a small ½ ton.

As far as gas mileage, we suspect they almost have to pull a gasoline trailer to keep the engine supplied!

1960-66 GMC V-12 Engine 1960-66 GMC V-12 Engine
1960-66 GMC V-12 Engine 1960-66 GMC V-12 Engine

1955-59 GMC Heater Control Panels

Tuesday, June 5th, 2012


For the first time in truck manufacturing General Motors made a heater available at the factory for Task Force trucks in the 1955-59 years. Yes, the dealer could still add a heater if you requested after the new truck purchase.

Here, we feature the GMC heater dash panel for these years. In the photo, the deluxe fresh air controls have chrome die cast housing, temperature control and defroster levers plus the fan speed switch. You could even adjust for inside or outside air intake.

The recirculator heater control also has a very interesting control panel installation. A hole is punched in the heater blank-out plate. A double switch is pulled to allow more water flow into the heater core. The same knob can be turned to operate the fan motor speed. See the photos with the remaining screen printed lettering on the plate. Very ingenious.

Another interesting photo is a GMC blank-out plate with the round heat knob. Here, the owner used the punched hole and an aftermarket switch. Of course, this is for fan speed and the water in the core is not regulated.

Note: The shape of the two heater inserts in the photo look as though they have a different bend, however this is only the angle of the photo!

Plaid Valve Covers

Thursday, February 11th, 2010

Strange but true, 305 V-6 valve covers on 1963 GMC 1/2 ton pickups came with a red, yellow, and black plaid design. The red color was used on the remainder of the engine without the yellow and black markings.

These photos are of an original untouched V-6 GMC engine. At this time, we are unsure why GMC used this appearance. (Maybe Scottish plaid implied good fuel economy.) Whatever the reason, it will be almost impossible for most perfectionists to restore a pair of the valve covers with the correct plaid appearance!

plaid valve cover 1

plaid valve cover 2

GM Vintage 1950 Overdrive

Thursday, February 11th, 2010

Chevrolet’s 1/2 ton and car overdrive 3 speed transmission was optional equipment installed on the assembly line during the 1950’s. The reduction of engine RPM’s in high gear resulted in less wear on the drive train as well as additional speed on level roads. Today, this is still important but of increased importance is better fuel economy.

The standard 3 speed transmission gives a 1 to 1 ratio in high gear. The overdrive is rated .7 to 1. The case and main gears are identical in both transmissions. The difference is in the rear extension tail. Here, the Borg-Warner gears electrically drop the RPM’s in the output shaft. GM’s wisdom created the 3 speed overdrive to be the same overall length as their standard transmission. This makes transmission exchanges very uncomplicated. There is no modification in the shift linkage rods or drive shaft.

With several basic tools a person can remove a standard 3 speed and add his overdrive in an hour! No problem if you don’t have the factory dash levers. Simply connect two insulated wires from the solenoid to a small dual position flip switch you add to the end of the shift lever. (It can be bought tat a local auto parts store and taped in place.) The driver can then shift in and out of overdrive using his thumb.

These overdrives were Chevrolet optional equipment from 1955 through the early 1960’s. Though they are becoming difficult to find, they do surface at swap meets, older salvage yards, and from owners totally modernizing their older vehicle. Find one and give your car or ½ ton a different personality!

Exploded View of GM 1950 Overdrive Transmission…PDF Click Here

First Year Oil Filter

Thursday, February 11th, 2010

It’s the first year for the successful Chevrolet V-8. (This basic small block design continues even today over 50 years later.) One very unique characteristic of this first year V-8 is the lack of a traditional block connection for a positive flow oil filter. For this one year, this 265 engine carried the by-pass oil filter system much like the standard 235 six cylinder. It was dealer installed!

The filter canister has a welded on right angle bracket that is secured under the thermostat housing at the front of the engine. The supply and drain lines are small like the 235. If the filter becomes clogged and the oil stops flowing into the cartridge, the engine continues to run with good lubrication. These photos show an excellent example of the 265 V-8 accessory oil filter system, with it being a dealer accessory, it probably was placed on few engines when they arrived at the dealership.

first year oil filter

1963-1966 Power Steering

Thursday, February 11th, 2010

1963-1966 Chevrolet Power Steering

Chevrolet linkage-type power steering is now available optionally on Series C10, 20, 30 models. This was formerly a dealer installed item. The equipment consists of a hydraulic pump, power cylinder, control valve, relay rod and hoses.

The power cylinder is mounted to the frame and is connected to the control valve through the hoses. The control valve is mounted on the steering drag link between the knuckle arm and the steering arm and it serves to control the flow of pressurized power steering fluid to either side of the power cylinder piston. This in turn pushes or pulls the tie rod as required for easier steering.

Power steering helps to combat driver fatigue and aids maneuverability. It also dampens road shocks and vibrations at the steering wheel and provides extra comfort and ease of handling.

1963-1966 Chevrolet Power Steering 1

1955-1959 Fan Shroud

Thursday, February 11th, 2010

1955-1959 Chevrolet Fan Shroud

By 1958 the Chevrolet V-8 fan shroud (not GMC) changed to the more traditional round design. During the V-8 beginning years in 1955-1957, it was little more than four pieces of custom sheet metal that helped pull air through the radiator core.

The enclosed pictures are of an original fan shroud for a 1958-59 Chevrolet 283 V-8. It fits only these two years of light trucks. Dimensions of the barrel is 19 inches in diameter and 20 inches deep.

The other shroud is from a 1958-1959 1 1/2 and 2 ton with V-8. There is a big difference. Be sure you purchase the correct design for the truck you have.

1958 1959 Chevrolet fan shroud 1

1958 1959 Chevrolet fan shroud 2

1958 1959 Chevrolet fan shroud 3

1958-1959 Pick Up (above)

1958 1959 Chevrolet fan shroud 4

1958-1959 1 1/2 – 2 Ton (above)

1955-1959 Starters

Thursday, February 11th, 2010

Two totally different 12 volt starters were used on the 235 six cylinder Chevrolet light trucks during 1955-1959. They attach to different bellhousings and are not interchangeable.

1955 1959 starters 1

As shown in the photos, the Hydramatic transmission starter has three bolt holes for securing it to the bellhousing. A solenoid on top reacts to the drivers key switch in the dash.

The starter for the 3 and 4 speed transmission has a top mounted foot start switch. It attaches to its bellhousing with two bolts

1955 1959 starters 2

1955 1959 starters 3

1955 1959 starters 4

1955-1959 Power Steering

Thursday, February 11th, 2010

Chevrolet’s linkage-type power steering is available as an RPO (Regular Production Option) on all models except Forward Control Chassis. New ease and fingertip steering control are provided because up to 80 percent of the steering work is done by hydraulic power. Maneuvering a heavily loaded truck in a small space becomes much easier, and straightaway highway travel is less fatiguing. In addition, power steering effectively damps road shock and vibration at the steering wheel.

A hydraulic pump, driven by an extension of the generator shaft, provides hydraulic pressure of 750-900 pounds per square inch. (A 30-ampere or heavy-duty 40-ampere generator is included with the power steering option.) The control valve on the Pitman arm reacts to movement of the steering wheel and regulates the flow of fluid to the power cylinder.

This valve directs fluid under pressure to either the left or right side of the piston in the power cylinder, thus providing assistance for both left and right turns. Manual steering, in case the system is inoperative, is always available.

1955 1959 power steering

1955-1957 Radiator Shroud

Thursday, February 11th, 2010

1955-1957

With the introduction of the new small block V-8’s in 1955 Chevrolet trucks, modified sheet metal was created to help in cooling. The new truck design came standard with the proven 235 inline six cylinder but when an optional V-8 was added, cooling modifications were necessary.

The short length V-8’s cooling fan was too far from the radiator and could pull air from above and below the engine and less through the core. To prevent this, all V-8 trucks came with an upper and lower metal baffle plate to help better pull air through the radiator.

These metal plates have become very difficult to locate in recent years. The lack of these two plates on (restored?) V-8 trucks are usually a strong indication the vehicle has been converted from an original six cylinder. The mechanic was either not aware these plates existed or had no idea of where to locate them.

During 1958-1959 the shroud was redesigned. It became a more traditional metal circle as is found on more modern vehicles. This allowed even more air to be pulled through the radiator core.

The following photos show original Chevrolet radiator cooling sheet metal from 1955-1957 V-8 trucks. The dark lines on the drawing relates to how these plates fit in the original vehicle.

1955-1957 Chevrolet Radiator Shroud

Speed Up 1948-1959 GM Pick Up

Thursday, February 11th, 2010

1948-1959 GM Pick Up

We often get requests for a formula to make the Advance Design pickups more freeway friendly. Their original ring and pinion gears were created to make the truck’s six cylinder work well with a load and also keep up with the 1950’s traffic on gravel roads and two lane paved highways.

Though a higher speed reproduction ring and pinion was introduced several years ago, some owners still ask for another alternative to get in the “fast lane”. One method has been used successfully for several years and requires most parts from local salvage yards. Obtain the Borg-Warner 5 speed overdrive transmission from an S-10 pickup. It must come from an earlier model with a mechanical speed sensor (on the side of the case). It can not have the more high tech electronic speed sensor as used on the later S-10 pickups with computers.

This transmission will bolt against the original bellhousing of a 1948 and newer (a nice surprise). The clutch shaft which extends out of the front of the transmission is usually too long to allow the ears to bolt flat and secure to the bellhousing face. Therefore, if this occurs, shorten the tip of the shaft about a half inch and all will fit together. This is a must. Otherwise you can even break off a transmission ear when you begin tightening the four attaching bolts.

The ears that attach the transmission to the bellhousing are usually drilled for a metric bolt. They will need to be enlarged for a standard 1/2 inch bolt as is threaded into the bellhousing.

The V-8 Camaro 5 speed transmission is also similar to the S-10. It is said to not be as low geared and this makes it more desirable. The Camaro shift lever is too far back for the 1948-59 pickup. The bench seat is in the way. To correct this, use the S-10 tail shaft housing and case top cover. This will allow the vertical lever to come through the original floor in the correct position.

The input shaft of the 5 speed will have either 14 or 26 splines. Therefore, the clutch disc must match the transmission and not the 10 splines from the original 1948-1959 truck.

The attractive S-10 boot is still available from GM and the shift knob of choice is from a late model 5-speed Jeep. It screws on perfectly and looks great! The S-10 shifter clears the seat cushion and looks like it was installed by GM.

The next step is the differential. An open drive shaft style will be necessary to match up with the 5-speed but this is a subject for an totally different technical article.

The result of this change is lower RPM’s and speed to keep up with traffic flow on most modern highways.

Casting Numbers

Thursday, February 11th, 2010
Casting Number Make Year CID
1970 Chevrolet 1964-1967 292
2135412 GMC 1946-1954 248,270
2193980 GMC 1952-1954 302
2324003 GMC 1955-1963 270
2324004 GMC 1955-1962 302
2404929 GMC 1955-1963 270
2192402 GMC Military 302
289890 Chevrolet 1963-1977 292
328575 Chev/Buick/Olds/Pontiac 1968-1984 250
328576 Chev/Buick/Pontiac 1968-1976 250
328880 Chevrolet 1963-1977 292
329990 Chevrolet 1963-1977 292
358825 Chevrolet 1966-1976 250
3629703 Chevrolet 1950-1952 235
366855 Chev/Buick/Olds/Pontiac 1966-1984 250
3692703 Chevrolet 1950-1952 235
3692708 Chevrolet 1950-1952 235
3692713 Chevrolet 1950-1952 235
3693374 Chevrolet 1942-1949 235
37001481 Chevrolet 1953-1955 235
3701946 Chevrolet 1953 235
3703414 Chevrolet 1954-1956 261
3733340 Chevrolet 1955-1957 261
3733813 Chevrolet 1958 261
3733946 Chevrolet 1954-1955 235
3733949 Chevrolet 1953-1955 235
3733950 Chevrolet 1954-1955 261
3737012  Chevrolet 1955-1957 261
3738307  Chevrolet 1958-1962 235
3738365 Chevrolet 1960-1962 261
3738476 Chevrolet 1958-1962 235
3738813 Chevrolet 1955-1963 261
3739365 Chevrolet 1958-1962 261
3739716  Chevrolet 1958-1962 235
3759365  Chevrolet 1959 261
3764476  Chevrolet 1958-1962 235
3769716  Chevrolet 1958-1962 235
3769717  Chevrolet 1959-1962 261
3769925  Chevrolet 1958-1962 261
3773949  Chevrolet 1954 235
3782856  Chevrolet 1962-1967 194
3782858  Chevrolet 1962-1967 194
378307  Chevrolet 1960-1962 235
3783949  Chevrolet 1953-1954 235
3788378  Chevrolet 1962-1974 292
3788406  Chevrolet 1962-1969 230
3788514  Chevrolet 1962-1970 153
3788813  Chevrolet 1955-1959 261
3789404  Chevrolet 1963-1976 292
3789412  Chevrolet 1963-1966 292
3789716  Chevrolet 1963-1972 292
3792852  GMC 1962-1966 194
3792858  Chevrolet 1962-1967 194
3821970  GMC 1967-1972 292
3833057  Chevrolet 1962-1970 191
3833067  Chevrolet 1963-1970 194
3833340  Chevrolet 1955-1957 261
383340  Chevrolet 1955-1957 261
3835253  Chevrolet 1942-1953 216
3835309 Chevrolet 1942-1949 235
3835335  Chevrolet 1942-1949 235
3835353 Chevrolet 1948-1952 216
3835363  Chevrolet 1954 235
3835374  Chevrolet 1942-1949 235
3835491  Chevrolet 1954 235
3835497  Chevrolet 1942-1953 216
3835527  Chevrolet 1951 216
3835692 Chevrolet 1950-1952 235
3835794  Chevrolet 1942-1953 216
3835846  Chevrolet 1953 235
3835849  Chevrolet 1942-1953 216
3835894  Chevrolet 1953 216
3835911  Chevrolet 1953-1955 235
3835917  Chevrolet 1954-1955 235
3835946  Chevrolet 1953 235
3835949  Chevrolet 1954 235
3836012  Chevrolet 1955-1957 261
3836223  Chevrolet 1955-1957 235
3836233  Chevrolet 1955-1957 235
3836340  Chevrolet 1955-1958 261
3836386  Chevrolet 1955-1957 235
3837004  Chevrolet 1955-1957 235-261
3837012  Chevrolet 1955-1957 261
3843363  Chevrolet 1953-1955 235
3850817  Chevrolet 1962-1978 230-250
3851656  Chevrolet 1963-1972 292
3851659  Chevrolet 1963-1976 292
3851859  Chevrolet 1963-1972 292
3854036  Chevrolet/Olds/Pontiac 1962-1976 230-250
3855914  Chevrolet 1963-1966 292
3855987  Chevrolet 1963-1971 292
3855991  Chevrolet 1963-1970 230
3856233  Chevrolet 1955 235
3858190  Chevrolet 1954-1955 235
3877178  Buick/Olds/Chev/Pont/GMC 1962-1978 230-250
3879875  Chevrolet 1962-1970 194
3886061  Chevrolet 1963-1966 292
3890011  Buick/Chev/Olds/Pontiac 1968-1972 250
3890013  Chevrolet 1968-1972 250
3892858  Chevrolet 1964-1967 194
389770  Chevrolet 1942-1951 216
3897702  Chevrolet 1942-1953 216
3921770  Chevrolet 1966-1976 292
3921967  Chevrolet 1964-1969 230
3921968  Chevrolet 1964-1976 230-150
3921970  Chevrolet 1963-1976 292
828575  Chevrolet 1972-1977 250
837751  Chevrolet 1942-1949 235
839770  Chevrolet 1942-1953 216
8397715  Chevrolet 1942-1949 235
839910  Chevrolet 1942-1951 216
839931  Chevrolet 1942-1949 235
8994256  Chevrolet 1964-1977 292
9890043 Pontiac 1968-1969 250

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

 

Muffler Tech

Thursday, February 11th, 2010

muffler tech

Prior to about 1962, Chevrolet trucks were equipped with round straight through mufflers. These units reduced back pressure and allowed the engine to breathe to its full potential. This caused a little extra exhaust noise in comparison to the larger more engineered oval car mufflers but trucks were for work and power.

About 1950 truck mufflers were given slightly larger inlet and outlet pipes. This allowed increased air flow which related to the slightly larger carburetor installed that year.

During the late 1960’s the Chevrolet truck Master Parts Catalog no longer listed mufflers. It appears they discontinued these units and left them to be provided by auto parts stores. By about 1995 the larger 1950’s straight through muffler was the one style available and any remaining older pipes were modified to fit 2″ inlet and 1 7/8″ outlets. Length is about 20 ½ inches.

The cars were lower to the ground and thus, required an oval muffler.  This oval shape allowed it to be higher and less likely to hit an object on the road.  Trucks were high and a round muffler was satisfactory.

Correct copies of these mufflers are available from Jim Carter’s Classic Truck Parts and a few other full stocking GM truck dealers.

 

Original Engines Must Breathe

Thursday, February 11th, 2010

Before the modern Positive Crankcase Ventilating System (PCV) most automotive engines breathed externally and removed their excess products of combustion into the atmosphere. It was a standard of the industry!

The lower end of the engine (below the pistons) had an attached draft tube that extended outside and below the block. It released blow-by from worn piston rings and other pollutants created from the crankshaft turning in hot motor oil.

The upper end of the overhead valve engine also must breathe. On early Chevrolet and GMC inline six cylinder engines, the venting is usually in the valve cover through factory slots. When an add-oil cap exists on this cover, it seals tight. It does no breathing.

On 1955-62 Chevrolet 235 six cylinders the valve cover slots were illuminated. It is assumed badly worn engines at high RPM leaked oil at these slots. The venting requirement was now moved to the oil cap. These redesigned caps have two features. They cover the add oil hole and vent the upper end of the engine. Their disadvantage is their internal filter can clog with oil vapors and dirt from a badly worn engine. This type venting cap must be kept clean!

The following photos show venting methods on early Chevrolet and GMC engines. Note the oil and breathing cap on the later six cylinder Chevrolet engines.

original engine 1

1937 through 1953 216 sealed oil cap (above)

original engine 2

216 valve cover vent slot (above)

original engine 3

1954 Chevrlot Vents (above)

original engine 4

1955-1962 non vented cover (above)

original engine 5

1955-1962 vented oil cap (above)

original engine 6

1963-1972… 230 and 250 with PVC system (above)

Venting the Differential

Thursday, February 11th, 2010

Sometimes overlooked by mechanics and restorers is a small vent in the rear axle housing. This part is necessary to keep internal pressure equal to the outside atmosphere. Thus, as the internal temperature of the differential warms during use, any expanding heated air is vented and no pressure occurs. This saves wheel and pinion seals from leaking.

Check for this vent in your truck. From years of abuse many vent assemblies are missing. A sliding log chain wrapped around the axle housing for pulling is a way many vent assemblies were accidentally removed. The owner usually didn’t know the damage has been done or that a vent ever existed. Now, the small hole that once held the vent assembly is able to take in water. This will certainly cause long term damage to differential parts.

Differential Vent 1

Differential Vent 2

1946-1972 3/4 Ton and 1 Ton Ring and Pinion

Thursday, February 11th, 2010

One series of the famous “drop out” GM differentials was used between 1946 and 1972 on 3/4 and 1 tons. The complete assembly (often called a pumpkin) will interchange during these years with no alteration.

The highest gearing in this series is the 4.10 ratio and is found in most 1967-72 3/4 tons with automatic transmissions. Therefore, those “low gear blues” often associated with 3/4 and 1 tons during the late 1940’s and 1950’s can be greatly improved with no visible exterior changes. Originally these older trucks had a ratio of 4.57 in the 3/4 tons and 5.14 in the 1 tons.

Once a 4.10 pumpkin is located (usually in a local wrecking yard) it is a basic interchange requiring little more than new gaskets and gear grease. Your truck’s personality is now changed!

This interchange will fit perfectly if the “complete” pumpkin is used.  The 1963-1972 carrier is necessary and it will be part of this total assembly.  The change-over will not work if you only use the ring and pinion.

The only negative to this changeover is if you are hauling a ton of gravel up a mountain road with the original smaller six cylinder!! In this example a lower geared differential is best.