I went today to look at an engine that is for sale and said to be a 261. With confidence, cash in my pocket, and my casting #s from here I headed out. The # on the block is not on our list. It is 3738004. I find 3838004 (235) & 3837004 (235). Does anyone have any info on this #?

Check for the captains bars cast into the side of the block (pretty good sign of a 261), I can't find the number either check with the Larowwes, these engines are their specialty.

'59 amd later 261s also had the big fittings and plug for the full flow filter system on the oil gallery (drivers side).

Did they make a claim as to what year it was supposed to be? "54 had the old style water pump, laters all had the long shaft pumps.

Another reason not to trust casting numbers (gig-gig). They can be helpful I admit.

It had a long water pump. I'll check the oil fittings. Captain's bars? Where are they? It has been sitting in a shop for a long time. Never outside. The stamped # by the distributor is F903B. There is rust in at least one cylinder from condensation I think. There was a wasp nest in the top radiator hose and one in the valve cover. The next time I go we will pull the head and have a look inside. There is also a two 1bbl Ellis manifold marked 270H. I'll get that.

Take a look here, scroll sdown for pictures., http://www.1954advance-design.com/Web%20images/261-engine/index.htm

if you get the head off: 3-9/16" bore is a 235, and 3-3/4" bore is a 261. Both have 3-15/16 stroke.

Just because the block has captains bars does not mean it is allways a 261. I have had several 235's with the bars.

Once we pull the head the bore and steam holes will tell for sure. It must be a '54 because the casting # is in front of the fuel pump. I'll try to get there Friday. Thanks for the help guys.

If its '54 then it has to have the early style short shaft water pump- a '55 or later pump has a deep tapered water pump pully, the '54 and earlier short shaft pumps have a shallow stepped pully-they can be swapped for the early 216 pullys that have the wide belts (and give a bored out 261 the outward appearance of a simple 216). adapt a fullheight 216 sideplate, the wide belt pulleys, adapt the 2-bolt valve cover, grind off the "captains bars", and it will take real expert to nail it as a 261. The early and late waterpumps wont swap, so you cant be too sneaky with a '55 or later block (235 or 261) but a '54 261 can be a stinker to catch.

Did I ever mention I dont trust casting/serial numbers?

The F903B serial number may be for a 1957 or later 235 with Powerglide, made in Flint, September 3, according to the Resto Pack information. What is the casting date code? It is located near the starter, as shown in this photo.

As edski said, the casting and serial numbers are just evidence, not proof, of what the engine really is. I have four 261s in my shop and only one of them has all numbers consistent with a 261. Factory replacement blocks can have casting codes or dates not consistent with the model year, and the serial number can be whatever the purchaser wanted to be stamped on the pad.

my new friend -thank you

Here is a few pics of 2 different syle 261 blocks that I have. Maybe they will show the water pump difference. They will also show that the date code does not really reflect the block style. In the case of my 54 block, it was a replacement motor cast in the 54 style but with a later casting date. http://rides.webshots.com/album/578167968KpVMeA

I also have a 1954 261 with the 3733950 casting number, same as that of Greg_H54's 54, and mine has a date code of F128, June 12, 1958. This date is probably correct, as the block was purchased, new, from a Chevrolet dealer in August of 1958.

The proof is in the pudding (whatever that means) - measure the bore and see the steam holes and siamesed cylinders.

GMCs are a lot easier! The 3837012 has the # in the same location as the one I'm looking at. I'll get all numbers next time plus pull the head. This is interesting to me. Thanks.

It's a 235. But the manifold turned out to be a Nicson GMC 302/270H. Sometimes you win and sometimes you win!

Sounds like a pretty good score.