Engine block question.......?

Greg Reimer 7376 · 09-19-2021, 08:11 PM

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 · 09-19-2021, 08:44 PM

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 · 09-19-2021, 09:08 PM

Quote:

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 itâ€™s a 402 casting. Too thin

Greg Reimer 7376 · 09-19-2021, 09:25 PM

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 · 09-20-2021, 06:55 AM

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

09-19-2021, 08:11 PM	#1
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,135 Likes: 172 Liked 704 Times in 218 Posts	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.

09-19-2021, 08:44 PM	#2
Tim H VIP Member Join Date: Jan 2007 Posts: 1,041 Likes: 1,068 Liked 481 Times in 158 Posts	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. Last edited by Tim H; 09-19-2021 at 08:53 PM.

09-19-2021, 09:25 PM	#4
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,135 Likes: 172 Liked 704 Times in 218 Posts	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.

09-20-2021, 06:55 AM	#5
Glenn Briglio VIP Member Join Date: Nov 2002 Location: Massapequa Park,NY Posts: 1,281 Likes: 1,892 Liked 969 Times in 307 Posts	Re: Engine block question.......? I"d still sonic test because it will then be a .060 over 396. __________________ 1989 Camaro Iroc-Z I/SA B&B Auto Machine Shop.