Inliners International Forums General Discussion Engines Identifing a 261.

Hello Inliners, a new Inliner here.
I've recently acquired a complete 261 out of a Canadian 1961 GCM school bus. The engine has been completely dis-assembled and is ready to go to the rebuilder to be cleaned and verified.
Here is what’s puzzling me, the casting # on the block is 3769925, and from what I've seen listed here on Inliners (and elsewhere), that translates to a 1958 to 1962 261 block.
The date code cast on the block is "C 1 6", this suggests the block was cast either March 1st 1956 or March 1st 1966. How could that be if the block is supposed to be a 58 - 62 casting? The other odd thing with this block is that there is no engine id number stamped on the machined pad beside the distributor.
Any insight from the Inliners is appreciated.

Thanks,
Alan

No ID stamping "could" mean it was a replacement engine. It was called to my attention that a 261 was a common swap in when 216s gave up. They were typically made with the 54 style water pump mount to be a more direct swap. I have a 54 style 261 that has as I recall the correct casting number but a later date code and no ID stamping as you mentioned. You may find something in this photo album that helps. It shows 2 different and different style 261s. http://rides.webshots.com/album/578167968KpVMeA

Hi AINiPa . . .

As Greg has pointed out the lack of ID on the dizzy pad suggests a replacement part. And it is also important to keep in mind that the casting codes could 'hold over' into the next year or more until new tooling arrived at a particular plant - this is why one can encounter a date code that is much later then the casting code would suggest. For example in the webshots links (Greg posted) it shows a 3733950 casting with a 1956 date code. But many sources suggest that during 1955 the tooling was supposed to transition over to a 3737012 casting number . . . suggesting that these transitions are not firm.

Since your engine is likely a replacement part it is conceivable that it was in fact built in 1966. As far as I know casting 3769925 was the last version for a 261 . . . so if GM continued to pop out replacements for fleet service they would have been with this casting . . . but this is conjecture on my part.

regards,
stock49