Engine block question.......?
 

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.

Re: Engine block question.......?
 

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.

Re: Engine block question.......?
 

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

Re: Engine block question.......?
 

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.

Re: Engine block question.......?
 

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