The Stovebolt Site Forums The Shop Area Engine Shop Correct Oil Pump for a 1956 261

Hey guys. Tring to find the correct oil pump part number for a 1956 261.
The pump that came out of the engine is GM 3701562, which checks out for a '54 261. However it is much longer than everything I'm finding at the various parts places.

Thanks!

deleted my post...due to me miss reading the OP question...

Mike B

That (oil pump) casting number/code number was/is for 1954/55st car, truck, and Corvette 6 cylinder engines.

He said oil pump.

The Melling M-45 pump fits all 235 and 261 engines, and with a little tweaking of the plumbing it might work on a 216. There are usually several M-45's on Ebay at reasonable prices. I'm working on an adapter to fit the oil pump for a 250 or 292 Chevy six to the early stovebolt engine- - - -it has bigger gears and more volume than any of the original equipment pumps.
Jerry

That is the number on the pump I pulled out of the engine. Which is why I'm double checking.

I only found one thread on VCCA w the part number and "261" ...so "checks out" was prob the wrong wording to use. lol.

Your wording worked for me.

Sorry, I miss read your original post, I had Fuel Pump on the brain...edited my post to prevent further confusion.

Mike B

The M-45 is much shorter than what I pulled out so the rest of the system doesn't really fit if adapted to one. That said, I'd rather use whats correct.

GM 3701562 brings up the '53 corvette mostly, which is why I looked into it possibly being incorrect for the bigger 261.

Is there a "better" pump than the M-45 for the 261?

That's the tech info I found too, also why I looked into it possibly being incorrect for the 261.


The M-45?

The 250 or 292 pump. I have machined an adapter that allows it to be mounted to the bracket for the OEM pump and driven by the distributor, but that procedure isn't for someone who thinks OEM is the be-all and end-all in every application. I'm more concerned with results than being obsessed with correct part numbers. The 250 pump also costs less than half the price of a numbers-correct pump. I've also adapted a small block Chevy water pump to an early Chrysler hemi engine, the one that's virtually nonexistent for the original application.

The Melling M-45 we put on John's 261 ran 40+ PSI at warm idle, and much more at highway speed.
Jerry

So the M-45 should be more than adequate for a 261, correct?
Any idea where I can pick up the rest of the system? Everything I pulled out of mine is set up for that other pump so it won't fit the M-45.

All it takes is some copper or cupro-nickel tubing and a bender. Once the pump is in place, make the lines fit the pickup and the pressure port in the block. The OEM tubing is 7/16" OD, which is extremely scarce, so upsize to 1/2" OD tubing and adapter fittings. You can use either inverted flare fittings or compression type with the slip-on ferrules over the tubing. Compression fittings are easier to use, but double-flared tubing and the appropriate fittings are better on the pressure side. Make sure the new lines don't contact the crankshaft, connecting rods, or oil pan.
Jerry

It's the pickup tube/screen I need. The one I have will sit too high with the shorter pump.

Without seeing the engine, I can't advise you about what you need. I've been fabricating appropriate parts for special applications so long that it never occurs to me not to just make something fit that's probably better than original. baffled high-capacity oil pans with special pickups for round track racers, for instance.

Why are you changing pumps? Is the original one that fits worn out or damaged? In 60+ years of engine building, I've seen fewer than 10 oil pumps that actually needed to be replaced. Most of them were badly scored from ingesting metallic debris.
Jerry

My builder says it could use a rebuild, says the housing where the shaft goes through is pretty worn, and in looking for a rebuild kit it's looking like it is the wrong pump. With no info on the pump that should be in there, we weren't sure if the one w pulled out (GM 3701562) would even work correctly.

The engine is a 1956 261 from a 3800 and the pump is a GM 3701562, which appears to be from a 1953 Corvette 235.

I found pics of a 55-57 235/261 pump w pickup and they look really similar to the Melling 45S2 pickup for the '58 235/261

What dimension of the pump you have is longer: the entire pump body? The tower? The actual gears?

The shaft and shaft housing are quite a bit longer. The input and output line sizes and locations are different too - the M-45 replacement in/out are side by side, where as the GM 3701562 are almost stacked and at a bit of an angle from each other.

Comparison pic: https://flic.kr/p/2jiJQkM

The one on the left is the GM 3701562, and the one on the right is the Melling M-45 replacement for the 235/261.

Since they all turn at the same speed, the pumping capacity is determined by the diameter and height of the gears.
The M-45 gears ar 1.00" tall by 1.50" OD, with seven teeth on each. It's the largest pump that fits directly that I know of, and is quite sufficient for a 261.

Cool. Thanks, panic (and Hotrod Lincoln)! At this point I'm going w the M-45 and just trying to find a suitable pickup for it.
I assume someone previously fixed the 261 I'm building with whatever they had access to, hence the '53-54 corvette 235 pump.

BTW, I added a comparison pic to my previous post.

The pump I just took out of a late-1940's 216 looks identical to the one with the taller mounting shank in your picture. I don't think I've ever seen a 235 or 261 with that pump as original equipment. The pickup in the oil pan on the 216 was bolted to one of the main bearing caps, with a tube running to the pump inlet. Since I'm going to be modifying that 216 engine extensively, I plan to fabricate a different pickup housing and screen, and run the 292 oil pump. It's also getting an increased-stroke 235 crankshaft, aluminum pistons, NASCAR connecting rods, and a few other modifications. The end result will be an engine that looks like a 216 from the outside and has 260+ cubic inches and full pressure oiling.
Jerry

So after checking my storage unit I'm pretty sure the tall pump (GM 3701562) that is on my buddy's bench is from my '54 261 block (no captain's bars) that was too far gone. The pickup is the "tub" type that bolts to the main cap rather than the disk type that screws into the pump.

The tub type pickup that bolts to the main cap and taller pump can be seen in the Installing The Oil Pump section of stovebolt's own 261 Rebuild page.
https://www.stovebolt.com/techtips/engines/261%20rebuild/lower-end.html

The Filling Station also sells the taller type pump for all '53-'54 cars and trucks and the shorter type for later 235/261s, if that means anything.



The disk type pickup that fits the Melling M-45 pump looks to be Melling part 45S2.

Have you been able to locate one of these pickup tubes ?

I would definitely run the M-45 pump and the tub pickup, and fabricate a custom line from the pickup to the pump. The M-45 gears are MUCH taller and flow more volume than the earlier pump.
Jerry

The pickups are generally set up for a particular pan. The best example I can give is the passenger cars. 55-57 pickup is slightly different then a 58, and the 59-63 is different then the 55-57 and 58 pickups. So the question is how positive are you that your block is a 56 production block? Any chance its a 54 early 55 style block cast in 56 as a service replacement? Any idea of what pan you are using? The 54-early 55 pans are slightly different then the later pans, and I am not sure of all of the variations of truck pans, if there are variations, from late 55 through 63.

Yes.

Is there a benefit to the tub type over the later disk type pickup? It'll be more work to make it fit at the correct depth so I don't really want to go down that road unless there's a benefit. Plus the 45-S2 is $3.99 so trying it out is a no brainer. We could always thread an extension on if needed.

No clue. lol. The numbers show it to be a '56 from a 6400. The pan came with the engine, which was still painted it's original yellow color, and has a variation in its side that my '54 261 did not have. From what I've seen the '58 pan matches this variation (an angle in the mounting surface only) which I assume was intended to keep people from mixing up pans with no other obvious differences.
Additionally, I've found nothing available from any vendor that is listed as fitting '56 specifically, just the '58, and we already know the M-45 pump fits both the Melling pickup and my block. In fact, I've found more info suggesting the 55-57 is the same and photographic comparisons that suggest the '58 pickup is similar to the '55-57 pickup. I can upload and post links to my comparison pics if anyone is interested.
Worst case, the 45-S2 pickup for the '58 261 can be easily manipulated to get to the correct depth.

I seem to remember a "floating" pickup screen on some late model engines that's pivoted at the end with the round screen on it instead of being rigid. No matter which one you use, be sure to measure the vertical distance from the pan rails and compare it to the depth of the pan so the pickup stays submerged below the "add oil" mark on the dipstick. The custom fabricated pans and pickups we used on the round track cars had swinging one-way doors and a pickup mounted so the engine wouldn't get starved for oil in hard left turns. Obviously, that's not a concern on the street.
Jerry

I ended up using the Melling M45 pump and Melling 45-S2 pickup for a '58 261. We had to bend it slightly to get it to sit flat and at the correct depth but it's gonna work perfectly and it was WAY easier than manipulating the 54's bracketed pickup.

Thanks guys!

I have a pump with a floating pickup. So far as I know it's a stock pump and I've never changed it. I'm interested in the idea of a M-45 pump as a rebuild is coming up in the next year or so. Will the floating pickup fit the M-45 pump?