The Stovebolt Site Forums The Parking Lot Big Bolts Block s/n 55F1017N: what's it tell me?

That about says it. My '48 2 ton Chev has, I know, a later engine, which last year I thought I had identified here as a 261. It does have Captain's Bars on the right side, low and to the rear of distributor. But now I read that a 261 also must have the same bars on the left side, center area near the top of the block. That's right under the exhaust manifold; I can't see anything that way. My head casting, (just under and inside rocker cover, left side), reads CONN12 and a little toward the rear, " J 10 6 " (Year code I think, but can't be sure meaning. I don't see the six digit casting number I read here is on 261's. I did search here and there are a lot of commentaries but I always seem to get confused.

From my serial number, above, what have I got??? Oh, that number is from the machined ledge on the right side of block, near bottom rear. Stamped in. The only part of it that was hard to read was the first 3 characters. But I'm pretty sure I got it right.

Enginew has a bent push rod, and I haven't tried to start it yet. Need to find a push rod and I've been dribbling light oil down the push rod holes. Rocker, etc., look nice and oily, but truck hasn't run for at least 7 years.

Comments appreciated, Dennis

55F1017N does not match the format for a car code or for a truck code. Someone will correct me, if I am wrong.

You might have a replacement engine that someone put an odd code on.

Find and post the casting codes and date codes: here are locations.

Thanks, TC:
Went back to look. Using your link to his 7 photos, I'll refer to each item by his photo number.
#1: block casting, found between dist. and road draft tube, inside 3 cast, "lobes." Nothing whatsoever on mine. In fact, there are no 3 lobes, but 2 lobes, down just a bit lower. NO number.
#2: Block date, right side, toward rear along with and just under captains bars. I have captain's bars, with, " CON 4," a little space, and, " 1 27 6 "
#3: s/n for engine on machined ledge, right side, as before, " 55F1017N
$4: Odd cast on number, right side, high on head between 2nd and 3rd spark plug: B46 848
850
#5: Head casting: I found it: 3836850 Also, "GM 1."
#6: Head date code, just inside valve cover:
J 10 6
#7: Head date, see No. 7.

On door post: 6RW K 3844, which is for the truck, not engine.

This help??? So, now...what have I got??? Why no engine casting number found? Somewhere else? Did find a lot of blue paint. Valve cover is held with the typical 4 quarter-inch slot head screws over tear-drop tabs. Breather is on front of VC.

??? Thanks, everyone. Dennis

Having written the above, I went back to try to help myself a little and found, apparently, that my head casting number is for a 261, built between 1958 and 1962. (Memory from what I just read a minuted ago) SO....now all that is missing is true identification of the block....

OK so far?
Dennis

Another possible spot for engine block casting number is to the right of the fuel pump.

If engine is in the truck it is kind of hard to see.
It is under a ledge, I stuck my camera down in the area and took a blind shot. Picture

I have also seen the engine block casting number where it says GM in the above picture.

On the surface one could read you number as.

55 = year
F = Flint
10 = Month
17 = Day
N = Engine 6000 Series HD (261)

But as TC said that's not the format used in 1955 1st or second series.

Then throw in the date code of Jan 27, 6 ...is this 1956 or 1966???

IF your block is a replacement the format is correct for 1966 (F1017N) except for the 55 prefix. Could this be a 1966 cast replacement 1955 model block and Chevrolet added the 55 to identify the model year and N to identify it as a 261?

Thinking out loud here...

Mike B

The way to identify it for sure is to pull the cylinder head and measure the bore size. A 261 will have a 3 3/4" bore and small holes drilled beside the cylinders on top of the block with corresponding holes in the cylinder head. A 235 will have a 3 9/16" bore, and will not have the steam holes.
Jerry

I'm starting to believe the folks who have posted the decoding info have it wrong. I have the same scenario for my 6400. The date code doesn't match up. Do you have a number cast into the block, on the passenger side toward the front, just above the pan rail? That seems to be the only consistent number that proves you have a 261. The list of 261 casting numbers is posted all over the internet.

distributor guy,

Do you have documentation regarding what is right?
What wrong information has been posted above?

The Engine Serial Number, 55F1017N, does not match the format of a GM code (links to GM codes for 1955 cars/trucks are given in a post above).

3836850 is a 1956-1963 261 head code. Here is one of the lists of 261 casting codes on the Internet.

As posted by others above, we need the block casting code to confirm a 235 or a 261. Locations have also been posted above.

I'm just saying the date code system seems to not be correct. I don't have proof of it, but my own engine and this engine are both anomalies. Mine quite honestly looks to have never been removed from the truck, yet the date code seems impossible. The casting number however is correct. I thought the end of US production 261 blocks was 1962. Am I wrong?

From what I understand, they produced 235 and 261 blocks up to 1976 in the US, most of them for export use in South America.

jorb: I tried everything I can think of to examine this left, rear block area just above the pan line and so far cannot see any numbers. That said, it is, indeed, very hard to see. My camera wouldn't do much as there are vacuum lines in the way of getting it in there. The other idea of pulling the head and measuring the bore is a great idea, but at my age and bad back, that's a tough way to go at it. I think this has been a very helpful thread so far, and I hope it assists others as it has done for me. This coming weekend I'll be tied up with other things for several days, so cannot pursue it until next month. Dang. Wish I could confirm block as a 261. Maybe someone else will chime in with more insight as to the 55 number in the serial number. Still hoping.... Dennis

Hope we are on the same page.
The location that I mentioned is to the right of the fuel pump.
Front of block area.
Under a ledge. Example: 3703414 Note: The white background where it says ENGINE CASTING NUMBER is covering ledge.
Might be covered in grease/dirt.

Yes, right front block area, not left rear. Passenger front. Like this photo in front of the fuel pump, toward the radiator:
http://photobucket.com/images/1954%20chevrolet%20261%20serial%20numbers

I have read that the 261 was also a factory option in some 1963 4x4 Chevrolet trucks. However, I cannot find that in the 1963 Specifications Manual.

This non-GM reference states 261s were available in 1963 4x4s until they ran out.

BINGO. Thanks to you all, I found the block casting number right where you said it, "could," be: Right side, far forward, way down and under ledge below the, "GM," cast letters. Lots of wiggling under the truck this morning. Took your suggestion and used my digital camera. Tight spot, but it captured the number:
3733950, which under another chart in another site, corresponds to 1954 or 1955 production 261.

SO - with that, any last ideas on where/what this danged engine, "55xx," serial number comes from??? 1955?

Thanks again; you all made the difference and I hope the thread helps someone else too.
Dennis

To review your numbers,

55F1017N..... Stamped on flat machined boss to left of distributor.

3733950....... Block casting number Right side, far forward, way down and under ledge.
1954-55 261 cubic inch

3836850....... Head casting number
1954-63, 261 cubic inch

J 10 6.......... Head date
1 27 6.......... Block casting Date,------ Is that a one (1) or the letter (I) or (L) ? It should be a Letter.
A = Jan.
B = Feb.
C = Mar.
D = April
E = May
F = June
G = July
H = Aug
I = Sept. 27, 195(6)
J = Oct. 10, 195(6) Head
K = Nov.
L = Dec. 27, 195(6)

6RW K 3844...Vehicle Serial Number drivers side body hinge pillar.
Serial #..... : 6RWK3844
Mfg Date... : November,1948
Model....... : 2 ton
Wheelbase. : 161 inches
Plant........ : Oakland, CA

jorb:
Thank you for the nice review. It all ended up great information. Regarding the month indicator, it must be an, "L," lower case, as the other doesn't make sense. Which, virtually, completes the information except the odd 55 prefix to serial number.
Again, thanks to all.
Dennis