The Stovebolt Site Forums The Shop Area Engine Shop Deciphering my Chevy stovebolt

Deve,

Thanks. You refer to "later castings". Which date code/codes are they?

Three 261 engines?

L 17 4 = 1964 replacement engine - has "ports" for both filtration systems.

G 2 2 = 1962 - no small port (no accommodation for by-pass filter)

G 8 1 = 1961 - no small port (no accommodation for by-pass filter)

My guess is the 1964 replacement engine was cast to accommodate either type of filter.
Is the water pump still mounted on that block?
High or low water pump on that block?

Thanks,

The 1962 is the other 925 and has the small port. Anecdotally, I have seen many more 261's with the small port than without. Before today, I didn't even know there was a casting without. Looks like the 717's will not have the small port but otherwise the same in function.

All of the later 261's had the lower waterpump as far as I know. All three of these and the seven 235's (all 1958-62) are low until I put Daves adapter on them.

The casting number below the distributor will be the first and most important number on the block. It would determine the features each part has. I learned all of this working at Midway Chevrolet in Moundridge, KS as a parts teenager when in High School. There may be exceptions, but for the most part if someone says they have a 717 casting, all 717's will have the same features regardless of the year or application. It would be really cool to have a list of differences in each casting for these years.

All 58-62 261's have the dowel and can be configured for either bypass or full flow. Never seen a 58-62 without the dowel.

It looks like the "717" casting (3769717) has been found a 1957-62 261 blocks.

Other 261 casting codes between 1958-1962 are (supposedly):
3769925
3769923
3836340, 3739365 (by Jim Carter?)

I show the 717 starting in 58. Do you have evidence they started in 57? That would be the first block pre-58 to have the Dowel then.

I have never seen the Jim Carter numbers or the 923 but that doesn't mean anything. Which ones do you have or have actually seen Tim? We should keep an eye out for people with 261's and see what they have.

Pic of 717 without small plug.

Casting lists drive me nuts.
There were so many changes between 1958 to 1962 that Chevrolet would not have carried the same casting number for all.

Yup. So far Dave we are all on the same page. That's three 717's without the small port. What bothers me about the list that Inliners has on its site, and they got that list from Jim Carter who gave me one of his original copies in the early 90's, is that it is very inaccurate. As I prove each one or changes need to be made, I make the changes on my site, but there is room for improvement for sure. Tim's efforts have really helped to sort things out as well. We should have a thread that asks for peoples casting numbers so we can confirm their existence.

Yes, if people with 261s would post the following information, it would be real nice:

1. Engine Serial Number (on pad to the rear of the distributor)

2. Block casting code (below/between the distributor and road draft tube)

3. Block date casting code (lower-left of the distributor side of the block - 1299 on this block) - (I 29 9)
I = 9 = September
29 = 29th
9 = 1959

4. Is there a small square-head pipe-plug to the left of the left oil-line port?
top of blue line is the pipe-plug

For the block in the images above, the info would be:
1. FO930LB (LB indicates a 1960 or later 60 series truck)
2. 3769717
3. I 299
4. yes, the little pipe-plug is there

Hello again gentlemen, I have a quick question. My truck (261 engine with Rochester carb) is giving me around 10 miles to the gallon combined. About 14 mpg freeway. I feel it's a bit on the low side. What do you gentlemen get with your 261's? Do the single barrel Rochesters have adjustments? It doesn't smell like it's running rich and it runs excellent. Any ideas?

What transmission and rear end in your truck?

What is your average speed on the freeway?

What year 261?

All of them would have had a single barrel Rochester.

It has a mixture adjustment screw (here is the simplest technique, without any other gauges/testers/equipment):
- run it until warmed up at idle
- adjust the idle speed to a slow but steady idle (500 rpm)
- adjust the mixture screw inwards until the engine gets rough
- adjust the mixture screw outwards until there is no change in engine smoothness
Step 1 and onwards at the lower right of this page.

That gets you a rough carburetor adjustment.

If you have a vacuum gauge, you can attach it on the port on the side of the intake manifold under the carburetor. Loosen the collar on the carburetor and rotate it until you obtain maximum vacuum. That gets you a rough timing adjustment.

Thanks Tim. I'll try that. It's the 1956 261. 4 speed. Don't know my rear end but I'm going 50 usually' my speedometer shows 45 with 6.00 16 tires. What kind of mpg do you usually get? What did they get stock? Thanks

They were stock only on big trucks (6000 series or 60 series, depending on year).

I'd get about 18 mpg at 50 mph in my 1954 1/2 ton Suburban.
I get around 12 mpg at 65 mph.
(3.55 rear-end and 31.5" diameter tires)

I see, so it looks like my engine is not tuned to its best performance. It's not too far off though. I'll have to tinker with it. Thanks for the help Tim.

How are you checking your speed and miles traveled? If you're actually doing 50 when your speedometer shows 45 then you're actually travelling 11% more miles than your odometer shows. That's not going to be a big difference but every little bit helps.

Thanks jfnar, that is something to keep in mind.