The Stovebolt Site Forums The Shop Area Engine Shop 59' 261 oil pressure

Hi, I am a newbie so I hope I am posting this in the right place. I just purchased a 1940 Chevy pickup with what I believe is a 1959 261 replacement block in it ( I pulled all of the numbers off of it that I could find and have been cross referencing) I have no idea what particular transmission I have. Transmission is a 5 speed manual. Weird thing is there is a circular gas pedal centered on the transmission directly in front of the stick shift. This is a restore project that was painted, and reassembly was started but never finished. The engine already had fresh oil in it. They were in the process of converting to 12 volt. It has new wiring harness and an alternator. I squirted some oil into the cylinders since it's been sitting for several years and turned it over with the spark plugs out to see what it would do. It turns over, and it is pumping oil into the external filter housing but the oil gauge registers no pressure whatsoever. I am assuming that they wouldn't have gotten this far into the restore with a motor that was no good, but I don't want to mess anything up before I get very far. My question is, will I register oil pressure when cranking or does it need to run to generate enough pressure to register? The second question involves the crimped oil tube that comes up to the rocker assembly. Someone previously JB welded the oil tube to the rocker cam? I plan on removing the JB weld to see what exactly I am dealing with. I am worried that I have a 235 head on a 261 block and that I am going to have issues with sufficient oil depending upon whatever work has already been done to this engine. Any help with identification of head vs block would be greatly appreciated.

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The casting number is indicative of a 261 head. Casting date looks like 62. Block looks like 61. So here is the deal with the rockers. 55-58 motors used a slightly different oil system and thus used a slightly different rocker arm. If you pull a rocker arm off one of these motors and look inside, you will see a groove that directly intersects the dribble hole. In 59, the oiling system changed a little and became sort of a pressurized system with some volume and pressure improvements. One of those changes was that the rocker arm assembly connector was now pinched off as opposed to the open end loop style of the 55-58. Also, if you look at a 59-63 rocker arm, the groove is now offset from the dribble hole to keep the rockers from spitting over the rocker arm and coil spring with the higher pressure. So given a 61 block and a 62 head, you would use a pinched off connector and offset grove rocker arms. The connector on your motor has been messed with and looks to be an earlier style connector that had the loop cut off and then cracked when the installer tried to make the lower part of the tube fit the head. You could clear off the jb weld and have someone braze it closed (the damage). And I would probably clean up the other end and crimp tight. That or source a proper replacement.

Also, if you look closely, you can see the connector is missing one of the spacers that keeps the spring in place. Replacements can sometimes be hard to come by so a good alternative is a valve spring shim. One other thing, and without having the rockers in front of me, at least one has been damaged a little, and a few look like someone may have enlarged the spit holes, at least on some of the rockers. If that turns out to be the case (and I cant really tell for certain looking at the photo so if you could use a drill bit and see if you can suss out what size the holes are and if they are all the same size, I can dig out one of my rocker sets and compare), you might consider getting another set of rockers. New Sealed Power units for 59 and up still turn up here and there. Otherwise, get a used set (make sure its complete) and send them to Rocker Arms Unlimited in California. They are the best in the biz and will rebuild them to perfection.

As an aside, that valve cover is the one year only 54 cover with the four vent slots. The slots were eliminated in 55.

I would suggest removing the distributor and spinning the oil pump with a 1/2" drill motor to see if oil pressure develops. Use a piece of 1/2" round rod with a flat ground into the end of it, or a large-bladed screwdriver bit cut off and ground to fit the slot in the pump drive. Spin the pump clockwise and watch the pressure gauge. I'd expect to see at least 30 PSI with that procedure, and 40 or more would not be unusual. As the engine warms up and the oil thins, the pressure will drop. 15-30 PSI at a hot idle would be normal for a relatively new engine or a recent rebuild. Max pressure at cruise RPM on a hot engine will depend on the tension of the oil pump relief spring.
Jerry

Flux,
Looks like someone enlarged the hole in some of the rocker arms. Maybe camera angle? Where is the line to your pressure gauge connected on the engine, don't see it in the pictures. The circular gas pedal is the original starter button, you stepped on that to start the engine. looks like you have a later starter that will work from the key switch. Spinning the engine with the starter you should see movement on your gauge. I have a 59 261 in my truck.

You Guys Rock! Thanks for the input. I'll look into the size on the holes in the rocker arms. I hadn't noticed that. The line to the pressure gauge comes off a tee right out of the block. I'll post a pic. So far, moving the engine with the starter I haven't see the oil pressure gauge move.

Thanks for all the input Dragsix. It looks like the engine is a hodgepodge thrown together from what was laying around? 61,62,64? A couple of my buddies were thinking the block was a 54 or 55. The cast date ending in 9 by the starter had me thinking 59' but the 3733950 is supposedly a 54'-55' 261?

I'll take a look at the rocker arms and see if the internal grooves are centered or offset. Given all the variables I was worried it was a mix of 235 and 261 and that the oil wasn't moving properly.

Good grief, I missed the 9! Yes, 59. I don’t think you will see much movement on a couple of bursts of the starter. Do the preoil as discussed above if you want to see some pressure at the gauge. Btw, a hodgepodge is just fine if it runs well, lol. My motors are frequently hodgepodge, lol.

Thinking 1962 was the last year for that generation engine.

The 261 was available on at least one Chevrolet truck in 1963.

3733950 was used from 1955-1957 (and, maybe in late 1954).

Find and post the codes found in 1, 2, 3, 6, 7, shown on this page.

You might as well ID what you have?

As far as I know yes for the 261, a little later for the 235 which one 4x4 truck application used the 235 motor for 63. That being said, I assume you might find blocks with casting dates later then 62 (service replacement) although the latest I have ever had is a 61 261 block.

I think the 261 was an option on the 4x4 in 1963.

That information from the 1963 Specifications Manual has been posted in the past.

That doesn't surprise me Tim. Common for GM to offer old engines in the next year models until they have depleted stock. They did the same thing in 1965 with the SS Impalas, offering the 409 until mid January when stock ran out and they started offering the mark4 396 engines afterward.

That could very well be. I always thought it was limited to the 235 motor and speculated that it had something to do with the design of the front 4x4 differential and frame and GM not having a replacement designed in time to use the then new style 6 motors. I will have to go dig around in my literature and see if I can find something.

I cannot find the 1963 info about a 261 being an option in a K-series truck.

Here is an old post.

Chevrolet Technical Service Bulletin .........plus
1963 passenger & truck ID info.

K10-20 engine suffix - J with a 235
K10-20 engine suffix - LB with a 261

235 & 261 on Page 8

1963 Truck 235 & 261 Power Trains

Thanks, Tom

I had mistakenly thought my memory was, as usual, playing tricks on me.
Documentation is the best cure.

Many thanks for digging that up! Always nice to learn something new.

Beautiful truck! Congrats.

Re-visiting this 6 month old thread. I think the 235 and 261 continued into 63 4X4 trucks only because of the frame. The K trucks had ladder frames and C trucks starting in 60 had X frames. The design of 4X4 frames with side engine mounts and trans crossmember mounts lagged behind the design of 4X2 frames... maybe.
Make any sense?