The Stovebolt Site Forums The Shop Area Engine Shop GMC 228 Confusion

Hey all, here's a fun one! I have a 228 that I have torn down. I know its a 228 because it says it right there aft of the distributor. I took it to the shop and was suprised when they called me back saying its a 248 with .040 overbore! Sure enough, cylinder diameter right at 3.74, not 3.6. Has anyone heard of this? Is the block on the 228 truly identical to the 248 so that this jump is possible?
Also looking for points of oppinion here... if it says 228 on the side, but is bored to 248, are we stock enough to be happy? I think im almost there myself. Im hoping to go as stock as possible, but I already know that the 47 has a 51 rear end.
Thanks!

How about block casting numbers? It's hard to imagine that an engine could handle a .140" overbore without developing a serious overheating problem due to thin cylinder walls, but it is possible that a replacement engine might have had the original ID number stamped to match the title of the vehicle. Maybe one of the GMC gurus can come up with some casting numbers to share with us. My father used to bore flathead Ford racing engines .250" oversize, but that required some very sneaky machining procedures, and they weren't expected to last very long- - - - -"Go fast- - - -turn left- - - -blow up frequently!"

Edit: Yahoo search is your friend- - - -one search, 15 seconds' worth - - - -

http://www.oldgmctrucks.com/Photos/GMC_Numbers.htm

228 block casting number: 6107326

248 block casting number: 6107328 or 2324002

I've also encountered a "256" GMC engine that has a 270 bore and a 248 stroke. It's Canadian military surplus, and doesn't usually get included in the USA engine size charts.

If you've got a 228 casting, it's probably way too big, bore-wise, to be reliable.
Jerry

All the replacement GMC six blocks that I have seen were stamped from the factory with the three displacement digits.