Mechanical

1954 Chevrolet Hydramatic Transmission

Monday, April 22nd, 2013


The first year of the Chevrolet pickup with a Hydramatic transmission was 1954.  Though it did not find a large percentage of buyers, this truck did open the door for an increasing number of this transmission in the coming years.

When sitting in the 1954 Chevrolet truck cab with this new option, some changes are immediately noted. To operate the starter motor on the original six cylinder, a button is pushed with the driver’s thumb just above the headlight switch.  The ignition switch still has 2 positions as earlier years.


The truck with a Hydramatic has an automatic choke on the carburetor, there is no need for manual pull choke.  Thus, GM installed a small blank out plug in the hole where the choke lever is usually found (at the left of the radio position).  At the right is another plugged hole which is usually for a throttle lever.

Of course, the main focal point is the Hydramatic shift selector attached on the column below the steering wheel.


For the new owner not acquainted with a Hydramatic, a paper sheet is slid over the sunvisor pad.  It lists the instructions for successfully operating those types of transmissions.


An interesting feature on the Hydramatic:  Turn off the engine while stopped in reverse and the transmission is in park!

Chevrolet Engine Oil Pump Screens

Thursday, October 27th, 2011

In the days when car and truck owners as well as mechanics did maintenance, GM made these responsibilities much less complicated.  An excellent example was the screen below the engine oil pump.

Due to no oil filters and no detergent additive in the motor oil (to keep dirt in suspension), the oil pump screen was necessary.  Tiny dirt particles settled to the bottom of the oil pan as was expected.  The small dirt particles finally became dirt chunks stuck to the bottom of the oil pan.

GM wanted no chance that a chunk or clot of dirt might be drawn to the pump.  Thus, oil pulled into the pump had to pass through this screen.

These photos show several early screens used by various Chevrolet six cylinder engines.  Note the used screen on the 1937-53  216 engine.  Its rounded screen is held in place by a single wire.  The wire can easily be unhooked from the housing.  The screen then drops out for easy cleaning.

Chevrolet Engine Oil Pump Screens
1929-36
Chevrolet Engine Oil Pump Screens Chevrolet Engine Oil Pump Screens
1937-53 wire holding screen 1937-53 wire unhooked to remove screen

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.

New 1952 Vacuum Advance

Thursday, February 11th, 2010

On the new 216 six cylinder engine, introduced in 1937, the vacuum advance was placed on Chevrolet trucks and cars at the right side of the engine below the distributor. A small metal vacuum line across the front of the engine connected to the carburetor base.

This vacuum advance design continued on trucks through the end of this family of six cylinder engines in 1962, however, on cars a change occurred in 1952. For cars, their engines began with new side motor mounts, not at the front of the block. For the vacuum line to get around this side mount the advance assembly changed position. See photo.

Note: When you see a parts book showing the vacuum advance changes in 1952, they are describing a car not a truck.

Using the 1952-1962 car vacuum advance on a truck will require modification on the vacuum line to a different bend. It will definitely not look correct!

new 1952 vacuum advance

1937-1951 Car and 1937-1962 Truck (left) | 1952 -1962 Car – (right)

GMC 302 Install in Old Chevrolet

Thursday, February 11th, 2010

The Trials and Tribulations of Installing a GMC 302 engine into a 1950 3/4 ton Chevrolet Pick Up

by Joel Baumbaugh

Background: About 5 years ago I “upgraded” the engine in my truck from a 216 to a 235. Lately I have felt that I wanted/needed a little more torque (especially while the bed is full of something heavy) and while one option was to rebuild and re-cam my 235 and another was to install a Chevy 350/400 (or 700R), the “popular” literature said that I could also install a GMC 270 or 302. Just to be “different”, I decided to go the latter route.

The Source: I wanted a “running” engine that I could just drop in with a minimum of trouble. The engine I found for my project was a 1959-1962 GMC engine from a School Bus. The bus had been converted into a “camper” and had then caught on fire and burned beyond repair. At first glance, the outside of the engine looked kind of rough. I checked the compression (all cyls. were at 160 lbs./sq.in), looked at the plugs (all light brown), listened to it run (no strange noises) ‘ the oil pressure was 55-60 lbs./sq.in. at idle and the rocker arms/valve area was pretty clean of sludge. Short of pulling the pan, this was as far as I could go. I bought it, brought it home and cleaned it up.

Problems/Solutions: The engine had a LOT of bus-type accessories that I did not want/need. The “massive” front Crank Pulley (the damper pulley assay) had a three-groove pulley ‘ “way” too long! After careful measurement I found that I was able to replace it with a single groove pulley off of a 235 (I replaced the front seal at this time). The water pump shaft was “very” long as well and sported a 2-groove pulley. I removed the pulley and ground/cut the pulley shaft back. The water pump on this engine did not seal against the block and/or head. This one was bolted to a thick steel plate which held a tensioner (for a double groove pulley) which weighed about 30 lbs. (weight I did NOT want) and was bolted to the front of the block. I found a rear plate (and gaskets) for the water pump from a place here in town that rebuilds water pumps. Bolting the water pump directly to the block saved me another ½ inch in engine length. The owner also sold me a flange to press on to the shaft so that I could bolt a new water pump pulley onto the pump (the original Chevy is shaft diameter is ½ inches and the 302 is 3/l8 inches). To find a pulley which would align with the bottom crankshaft pulley required a number of trips to local junk/wrecking yards. I finally found one that was the perfect depth (I’m not sure if it was originally from a Chevy or not). I had to enlarge the center hole to make it fit the GMC shaft.

The 302′s “bus” generator weighed about 80 lbs. I found that the 235′s generator mounting flange’s bolt-holes fit perfectly! However, I “did” need to reverse it and then elongate the mounting holes so that I could slide it forward to align the generator pulley groove with the crank and water pump pulleys.

The carburetor that came with the engine was a joke. It even had a governor on it. I had the option to purchase a better 2-barrel carburetor or to step up a little bit and buy a 4-barrel manifold. I did the latter. I had a (gasp) Ford ‘Autolite’ carburetor in my garage (about 400 CFM) from a ’289′ which I bolted up to the manifold and it works GREAT! – Especially with the stock low-performance camshaft. I also at this time “upgraded” my carburetor linkage. I went to an off-road dune buggy place and purchased a new accelerator pedal and a push-pull cable. Configuring the carburetor linkage from the stock pedal to the new manifold/carburetor would have been a nightmare otherwise.

Radiator: The 302 engine “is” 1 1/2 to two inches longer than the 325 (which is longer than the 216). This means that the radiator no longer fits into its original location. I tried to modify the radiator mount to put the radiator inside. Don’t even try. The radiator needs to mount on the front of the mount. This means that you will have to borrow your neighbor’s “Saws-All” with a metal cutting blade and cut away the top and front cross bracing on the radiator support, the lower front wind deflecting metalwork at the bottom (behind the grill) and drill 6 new holes in the mount for the radiator. The upper support that contains the hood latch will need to have a rectangle cut in it to fit the top of the radiator in it as well. I now have about 2 inches clearance between my water pump pulley and the radiator. I use an electric thermostatically controlled (pusher) fan in front of my radiator. It’s quieter, doesn’t rob the engine of power (better mileage) and the water pump may last longer without the fan blades. Note: My friend and neighbor has a 1951 GMC. I have measured his engine compartment. From his bellhousing to the radiator flange he had 4 more inches to play with, so I’d bet that he originally had a longer GMC engine (he runs a Chevy 235 now), and that he could make the conversion to a 270 or 302 without any cutting being necessary.

Front Mount Yes the 302 engine “is” 1 1/2 to 2 inches longer than the 235. The front mount on the Bus’ 302 was a weird set-up which caused the engine to sit at an angle (like a Chrysler slant 6). This saved some height in the bus’ engine compartment. However, after removing the bus setup spacers, I found that the two bolt holes on the mount (on the bottom of the timing cover/block) were at right angles to the block and aligned perfectly with my truck’s original 216 mount so I was able to exchange them and everything was level ‘ no oil pan removal required! I then drilled two (new) holes through the truck’s cross member, put in longer frame-mounting bolts and added some extra rubber padding (cut from a truck mud-flap) to keep the mount from rubbing on the frame and so far its worked ok.

Rear: The bus engine I purchased was coupled to an automatic transmission. That meant that it had a flex plate (that the converter bolted to) instead of a flywheel. The flex-plate (with the old ring-gear) was MUCH larger than the flywheel I would need. I found a flywheel from a GMC 270 that fit. Although the flywheel’s diameter and the number of teeth are the same as the 1955-1959 Chevrolet, the crankshaft bolt pattern is different between the GMC’s and the Chevrolet’s. The flywheel bolts are different as well (1/2 inch dia. instead of 3/8′s”). Although I tried using an impact wrench, a gorilla on steroids must have put on the old flywheel bolts. I broke a socket and finally had to remove 3 of them with a chisel. The 3/8″ GMC flywheel bolts are not available ANYWHERE. I went to an industrial bolt supply place and bought six more grade 10 bolts. I had the heads machined thinner (like the originals) as otherwise they protrude into the pressure plate/clutch plate area and will cause binding problems. I then carefully shortened the bolts (watch those threads ‘ I put a tap on the inside of the bolt and then backed it off to remove the burrs) to match the original length as they otherwise hit the block behind the flywheel (close tolerances here…).

The pressure and clutch plates and throw-out bearing match those of a Chevy 1955-1959 10- inch set. The 302 had a roller bearing pilot bearing instead of a oillite bronze bushing. I replaced it with another roller bearing and the transmission (its a Saginaw off of a 1969 Camaro) fit in just fine.

I used my original bellhousing off of the 1950 Chevy. The old GMC one was slanted to match the front motor mount. The starter location in the GMC bellhousing was for a larger diameter flexplate and would not work. The GMC starter had the wrong number of teeth to work on the 10″ flywheel. The starter which (I found) works, was a 12 volt 9 tooth (for a 164 tooth flywheel) from a 1955 Chevrolet and works great.

Oil and Water lines: There is an oil line on the front of the block up to the head. This supplies the oil to the rocker arms. Leave it alone. I tied (T’d) into it and put on a 100 PSI oil pressure gage as my Chevy gage only goes to 30 lbs. This engine NEEDS an oil filter. If you block off the oil supply line on the driver’s side of the block you will not get ANY oil pressure in the engine. I “T’d” into the pressure side and connected up my original oil pressure gage (it’s a stretch, but it reaches). Yes, it’s always pegged on 30 lbs., but gives me a warm fuzzy feeling when I look down. The head has an external water line that goes to the thermostat housing. Leave it alone. You can put a “T” in and hook up your temperature gage (with an adapter), but I put mine further down on the block (there’s a fitting there), because it was always showing “cold” on the gage. Be careful of that temperature gage line. It cost me close to $50.00 the last time I had to replace it. The radiator hoses clamped right up although the GMC diameter on the lower radiator hose is one step smaller.

The 302′s distributor had a governor on it and was centrifugal advance only. The bottom of the distributor was different than the Chevy, but my Chevy distributor “guts” bolted right in. I was able to put in a spring kit (the GMC centrifugal advance springs were so thick that they could have been used for front struts on a Honda) and I now have vacuum advance as well.

The GMC fuel pump leaked so I replaced it with a Pep Boys electric fuel pump. I couldn’t find a replacement anywhere locally, so I guess I’ll have this one rebuilt for a “spare”.

I had a split cast-iron exhaust manifold on the Chevy 235. I “may” get a header for this motor in the future, but in the mean time I had the muffler shop split the 302′s three-inch header pipe into the two existing exhaust pipes.

And, how is it?

Well, pretty good. I have a LOT more torque. This means that I can get up to freeway speeds without wishing for bike-pedals for a little more push. I have 36″ tires on 6″ Chevy rims on the back so I’m only turning 2,800 RPM at 60 mph. The larger tires had made the truck a little “logy” getting started with the 235 ‘ now it “steps right out” from a light. I haven’t checked the gas mileage yet. I was getting 17 mpg City and 20 mpg highway with the old 235. I’d guess that I’ve lost about 2 mpg with this engine/carburetor combination.

Future When this old engine is due for a rebuild, I’ll probably buy some “lighter” pistons and a little hotter (than stock) cam. The pistons will help the engine “rev” faster, be easier on the bottom end and will probably result in higher gas mileage due to their weight difference and the higher compression. The cam will help volumetric efficiency and give me a little more torque and higher end. Of course I’ll have everything balanced ‘ IMHO it’s worth the extra money.

I hope that this story helps someone else. Remember the 270 and 302 are “basically” the same engine so I imagine that your situation will be pretty similar to mine no matter what you find. It took “6 hours” using hand tools to remove the old engine and 4 days to put back in the new.

Joel

UPDATE

Since the project above, I decided to rebuild the 302 as it was burning a little oil. I bored the cylinders out .125 thousands (it’s now 320 cubic inches), put in a “Patrick’s” M4F camshaft, and put in “Venolia” 10.5×1 forged pistons. I had everything balanced of course. I had to find and purchase another head as the old one had a crack in it (hence the oil burning). When I got the new (used) head, I pulled out the valves and cleaned/smoothed up the intake and exhaust ports/passages which were pretty rough castings, and then put in new late-model exhaust valves (I went to 1.5″) and hardened seats for unleaded gas, and I’m using Chrysler “440″ valve springs. I’m now running a “Holley” 600 CFM carburetor (vacuum secondaries) with “Fenton” cast-iron headers. When first started up on a dyno (and not really broken in yet) it recorded 286 hp and 362 ft/lbs torque; not bad for a “street” engine; At this time I also put in a T-5 GM transmission from a ’91 V-8 Camaro (the V-8 transmission has better bearings to handle the torque) with a tail-shaft from a S-10 Pick-up (the shifter was almost in the same place) – so now I have a 0.74 overdrive. At 75mph (a fender-slapping speed for the old pick-up) I’m only turning 2,100 RPM; I had a new driveshaft made as the transmission yoke splines on my old one looked worn.

So far, I’m pretty happy with my set-up. Happy “wrenching” everyone;. ..jb

Joel Baumbaugh

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

1947-1955 Air Filter

Thursday, February 11th, 2010

During the Advance Design Truck years, two air filters were available when an order was sent to the factory. The base air filter (no extra cost) was the oil-wetted design from earlier years. The owner was expected to place a thin layer of motor oil on the filter media. Dirt particles would be caught by the oil as it passed through the mesh material. This metal mesh looks much like the material in a kitchen pot and pan copper scraper. The owner was reminded to clean the mesh every 2000 miles for it to be effective.

For an extra $5.00 an improved oil bath air filter came with the new truck. Most everyone who used their GM truck for work duties chose this filter. It required less maintenance and was more forgiving if neglected. GM recommended cleaning in kerosene each 100 hours or 5,000 miles minimum. Part of the filter media actually sets in an oil reservoir that has a pint capacity. The oil is slowly drawn up into the filter material and collects dust particles as the air travels to the carb. * NOTE: For best results use non-detergent oil. Dirt is not held in suspension with non-detergent oil and it settles on the bottom of the reservoir. At the same time held particles slowly sink toward the oil reservoir and accumulate at the bottom. Thus, this filter is always effective due to the oil upward movement. When the oil is changed in the filter pan or reservoir the dirt is also removed.

As with other manufacture’s air filters, they will cause fuel mixture problems when not maintained. A very dirty air filter will restrict air flow into the carburetor and result in increased fuel consumption.

1947 air filter 1

1947 air filter 2

Oil Wetted (above)

1947 air filter 3

Oil Bath (above)

1947 oil filter 4

Oil Bath (above)

1947-1948 Accelerator Rod

Thursday, February 11th, 2010

1947-1948 GM

By January 1949 GM realized there was an engine noise in the new late 1947 Advance Design cabs that needed correction. If a truck customer complained, the dealer was given a solution by modifying a part from a Chevrolet car.

The problem was engine noise entering the cab through the horizontal accelerator rod where it touched the floor hole. On many early Advance Design models there was not yet a pocket to hold a felt floor seal and insulate this rod. Metal to metal contact was inevitable.

The enclosed article is from a GM product service bulletin issued January 31, 1949. It was sent to all dealers.

Note: It is doubtful if all this work required of the dealer in the bulletin was ever very successful. The real noise problem was actually from attaching the back of the accelerator pedal to the accelerator rod. Metal contact here brought noise into the cab and then to the floor where the accelerator pedal made connection. By 1951 a new pedal to rod connection was used (like the car) and the problem was corrected.

1947 GM accelerator rod 1

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! This 261 was available only in 2 ton (6000 or C60 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 37369717 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

 

Closed Drive Shafts

Thursday, February 11th, 2010

Occasionally we hear owners condemning the closed drive shaft system used in the 1/2 ton trucks prior to 1955. After questioning the negative comment, we almost always discover the real criticism is the low gearing of the ring and pinion in the differential. Yes, this lower gear ratio was created more for slower roads of year gone by, but it is by far not a poorly designed system. In fact, it is questioned if there has ever been drive shaft and u-joint combinations that exceed the durability of this GM quality engineered closed unit.

Over 50% of the surviving older 1/2 ton pickups continue to use their original closed systems. Of these, the majority have had little or no servicing other than keeping lubrications in the transmission and differential.

Consider this when you realize the last GM closed drive shaft system was produced in 1954. Many others have been in irregular service prior to the 1920′s. Also remember that many 1/2 ton pickups were often given abuse far in excess of the manufacturer’s recommendations.

What modern open drive shaft system has been able to compare with this unsurpassed record? None!! Sure, the newer open u-joints are easier to change. They better be. They require attention or replacement so much more frequently!

Another Example of GM Quality!!!

We recently received the following comment from John Berkeley Ball. He also confirms the quality of the General Motor’s 1/2 ton closed drive shaft and differential.

Dear Jim Carter

Thanks for your excellent articles. One very pertinent point I feel that you should mention about closed drive shafts is their absolute impervability to rear spring wind up. Used on the farm over soft ground with heavy loads, you could not afford to send your rear end into drive breaking pulsations every time you lost traction, whether the shocks were worn out or not (some were single action any way). What a huge advantage over the Hotchkiss rear end! this is an often unknown design attribute that Chevy engineers were unfoundedly maligned for – at least by today’s city slickers…

John Ball

You may relate comments to this web site or Mr. Ball direct at john_ball@telus.net.

216 Oil Leaks

Thursday, February 11th, 2010

And now we’ve seen it all! A real example of American ingenuity.

Designed by an aftermarket company to keep an over tightened valve cover from leaking motor oil down the engine sides.  A metal band is pushed over and around the base of the valve cover.  Brass U-brackets are then secured by the two valve cover studs.  This creates equal pressure around the valve cover perimeter to stop the leaks down the side of the engine. 

Scott states he has seen these brackets on another 216 engine. Maybe a company in that area once offered them at local auto parts stores.

This photo was taken by Scott Golding, a resident of Western Nebraska.


216 Oil Leaks

E-mail scottandbetty@hotmail.com. Scott states he has seen these brackets on another 216 engine. Maybe a company in that area once offered them at local auto parts stores.

Your opinion is welcomed.

 

1938-1953 Clutch

Thursday, February 11th, 2010

Chevrolet introduced their basic nine inch single disc clutch and corresponding diaphragm pressure plate in 1938. This pair was used in their cars and most 1/2 ton pickups with three speed transmissions through 1953. With about one million of these vehicles sold annually, one can quickly realize the high numbers of this clutch system that was at one time on the highway.

Even in 1954 with the introduction of the larger ten inch clutch disc and modified pressure plate on the new 235 six cylinder, the original design continued to sell very well as aftermarket replacements. Today, they still have a strong demand even though the majority of these over fifty year old vehicles are history. Most auto part stores now keep a pair in inventory for their walk-in customers.

1938-1953 Clutch

To add even more validity to this clutch’s durability, GM reintroduced it in the late 1960′s. General Motors was a major producer of full size passenger buses and the demand for most having the optional air conditioning was becoming strong. Almost all new buses would now be equipped with the option. The original small nine inch clutch was combined with the newly engineered large bus AC compressor. Once again, this proven clutch was serving automotive needs!

Therefore, if you find a source for new or core clutch assemblies used from the late 1960′s to at least the mid 1970′s in GM buses, they will also fit 1938-53 cars and small trucks.

Motor Oil in Old Engines

Thursday, February 11th, 2010

Prior to the mid 1960′s, motor oil did not have the modern detergent additive. Therefore this type engine oil didn’t keep dirt particles in suspension. Foreign material would slowly settle to the bottom of the oil pan and on other flat surfaces such as the valley of the head.

If you ever removed an oil pan from a 50 year old engine that has been setting, chances are good there can be up to 1/4 inch of sludge in the bottom. This is not a bad thing! The non detergent oil has allowed the dirt to settle. As most 60 year old engines did not have an oil filter, this dirt settling was what should happen to increase the engine life.

The problem begins when a new owner wants to get his old vehicle running. He installs plugs, points, back-flushes the cooling system and changes oil. Oops, he probably adds detergent motor oil! The dirt deposits now begin to slowly go back into suspension. Unfortunately with no oil filter the dirt stays in the oil and shortens the remaining life of the engine.

Moral: Add non-detergent oil if the engine has no oil filter.

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.

 

Okie Bushing Installation (Just Before Installing)

Thursday, February 11th, 2010

okie bushing

The Problem

The closed drive shaft ( on GM 1/2 ton, 1937-54) is supported at the front by two bushings. As these wear egg shaped over many miles, the drive shaft begins to move up and down. This ruins the grease seal and causes the u-joint to begin rubbing the “bell”. Thus noise and vibration!

Finally, with a bad seal, the differential fills with transmission grease running down the drive shaft starving the shifting gears. Then, the rear wheel seals leak, the brake shoes become oil soaked, and finally the u-joint flies apart from rubbing the bell.

The Solution

Catch the developing problem early and save much expense and down time. Install what is sometimes called an “Okie Bushing”, an aftermarket, non-GM repair. This is a quick, permanent fix that does not require tearing down the differential!

Instructions

Remove the u-joint bell retainer and slide this bell back, exposing the u-joint assembly. Disassemble the u-joint by removing the four bolts. The rear u-joint yolk can now be slid off the 17 drive shaft splines, exposing the grease seal in the drive shaft.

Pull out this seal and the front egg shaped bushing from the torque tube. Sometimes this bushing is difficult to remove and special pullers can be rented. Otherwise, call Jim Carter’s Truck Parts at (800) 842-1913.  They have these pullers made.

Press in the long Okie bushing – seal first. Placing a wood block over the bushing end and tap into the drive shaft housing (torque tube) with a hammer.  This action will then press the other original rear bushing back out of position. The new Okie bushing will now hold the drive shaft in perfect alignment, as when the vehicle was new.

They used to advertise this as a permanent half-hour fix.  This is optimistic but so much easier than disassembling the differential as the Chevrolet dealers did 50 years ago.

 

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)

Sloppy Floor Shift Lever

Thursday, February 11th, 2010

sloppy floor shift lever

Problem: Slop in the shift pattern on 1937-47 Chevrolet 3 speed transmissions.

When shifting into 2nd gear finds your knuckles contacting the glove box door, repairs are needed

Repairs:

Chevrolet did not plan on these 3 speed transmissions to be in use over 50 years so repairs in this area were not often discussed by GM. You can fix it anyway!

Remove the flat plate with the shift lever from transmission by taking out the 4 retaining bolts. (Be sure to replace this plate with cloth or cardboard so no foreign object falls inside.) Take the shift tower from the flat plate top by removing four retaining bolts. The shift lever and its 2 1/4 inch tension spring can now be taken from the tower.

Inside the top of the tower is the worn brass bushing causing most of the shift lever slop. A replacement with tension spring can be obtained from Jim Carter’s Truck Parts and most of their full stocking dealers.

1937-1947 3 Speed Shift Repair

Shift Pin

Sorry, exchanging the brass bushing will not solve all the problem. The long horizontal pin, through the shift lever ball, needs to be replaced. The pin will probably be worn on each end and needs replacement.

Using a drill bit is a good option for a new pin. If a 1/4 inch drill bit easily moves into the shift lever ball, move up to the next size. (Maybe as much as 9/32 inch drill bit). Use it to drill the hole oversize, then use this same drill bit as the new pin. After drilling, remove the drill portion on the bit, and you have a nice hardened pin! Note: do not cut the drill bit until you know the exact length needed. Get a correct size by turning the shift tower upside down and measuring the distance between the two notches to the tower walls.

Timing Gear

Thursday, February 11th, 2010

About 10 years after the introduction of GMC’s new inline six cylinder engine in 1939, General Motors issued a ‘Product Service Bulletin’ in regards to a recommended improvement on the 228, 248, and 270. It appears the manufacturer discovered a weakness that shortened the life of the engine timing gears. This recommendation was made for enlarging the oil supply hole leading to the meeting point of the two gears. The attached dealer bulletin was issued January 31, 1949.

This is especially interesting considering over a million GMC trucks with these engines had been built prior to this. The number includes the five years of military large trucks that were used during WWII under very abusive off road conditions!

tming gear

Water Pump Modification

Thursday, February 11th, 2010

If you use a recently manufactured 216 water pump and combine it with the optional larger OEM radiator fan, a slight modification is necessary. The fan rivets will not clear the edge of the pulley hub. You must cut four notches in the hub for rivet clearance. Water pumps in the last five years appear to lack these notches.

Note: These larger fans, 18″ long, were optional on smaller trucks and always came on the 1 1/2 ton’s. It is the 15″ fan that will usually be on small trucks and passenger cars.

Comments courtesy of:
Bob Adler, Stephentown, NY.
bobadler@nycap.rr.com

water pump modification

Notice the four notches cut on the outer rim of the hub. (above)

water pump modification

Hub and Fan. (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 is certainly not good for the internal differential parts.

Differential Vent 1

Differential Vent 2

1946-1972 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.

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