Engine block question.......?

[Greg Reimer 7376]

Got a big block Chevy bare block, needs cleaning, kinda dirty, block number on back is 3969854.One part number decoder says 1969-1972 402. I took a cast crank out of it, it was a 3.76 stroke 402. One of our local big block Stock racers wound up with that, but the same decoder shows that same casting number as going with a 454 truck engine,70-73 vintage. Is this some kind of thick walled block for the 402 that could be decently sized out to 4.250" or is this a thin wall 402 block? The stamping on the passenger side deck surface in front of the right head says T 1118 TBG which indicated a 70 402 truck engine,310 horse. Any big block authorities think this might be some kind of thick-walled block that could go 4.250" bore size? Thanks in advance.

[Tim H]

I've never seen an "854" block in any OE displacement other than 402. Not aware of any successful 4.125 bore blocks living with an overbore to 4.250." At .060 over I would think the cylinder walls would be dangerously thin, because it is already .030 over from the factory.

[Glenn Briglio]

Originally Posted by Greg Reimer 7376

Got a big block Chevy bare block, needs cleaning, kinda dirty, block number on back is 3969854.One part number decoder says 1969-1972 402. I took a cast crank out of it, it was a 3.76 stroke 402. One of our local big block Stock racers wound up with that, but the same decoder shows that same casting number as going with a 454 truck engine,70-73 vintage. Is this some kind of thick walled block for the 402 that could be decently sized out to 4.250" or is this a thin wall 402 block? The stamping on the passenger side deck surface in front of the right head says T 1118 TBG which indicated a 70 402 truck engine,310 horse. Any big block authorities think this might be some kind of thick-walled block that could go 4.250" bore size? Thanks in advance.

If in question on cylinder wall thickness get it sonic checked. And yes it’s a 402 casting. Too thin

[Greg Reimer 7376]

Doesn't surprise me. Would that block be OK for non-racing use at 4.125+.030" if it is relatively free of core shift? I'm talking along the lines of a stock rebuild.

[Glenn Briglio]

I"d still sonic test because it will then be a .060 over 396.