[Gusjohns]

My sbc casting # is 3932371, it shows a 69/73 307, but the block has a 4" bore and 4 bolt mains. Was the casting # also used for 350 4 bolt blocks?

 

[BogiesAnnex1]

No, that block was not used by the factory for 4 inch bore engines. But it is a time when 307s would tolerate a bore to almost 4 inches and it was popular to build 302’s (actually 299’s to 301’s) on that block but that doesn’t leave any meat in the walls for another bore job.

Four bolt mains are most likely aftermarket as well.

Bogie

 

[Gusjohns]

No, that block was not used by the factory for 4 inch bore engines. But it is a time when 307s would tolerate a bore to almost 4 inches and it was popular to build 302’s (actually 299’s to 301’s) on that block but that doesn’t leave any meat in the walls for another bore job.

Four bolt mains are most likely aftermarket as well.

Bogie

That's interesting, if it's a 307 block, then the 4 bolt main caps look factory, complete with GM casting #s. It's a 4" bore that just needs cleaned up. Thanks for the insight.

 

[Gusjohns]

 

[Gusjohns]

It's a 307 block with what looks like factory 4 bolt mains, the bore is 4 inches, but needs a cleanup, can it be safely honed/bored .030? I would like to use this block since I already have it. The bore has pitting in it.

 

[RWENUTS]

Where’s the pic of the casting number?
And the suffix code pad?

 

[BogiesAnnex1]

The only things I can say is one of the most prominent things about GM block castings is their attachment to finish bore size. GM and everybody else does not include more cylinder wall thickness than necessary, they sell this as weight reduction but it’s really about saving money on raw materials. Every reference to the casting number you sight says this is a 307 block which uses a 283 bore of 3.875. Now the literature may all come from copies of the same original place so if that was wrong then everything in the known universe is wrong. I used to have a factory engineering book of GM casting numbers at the shop but it “disappeared” about 10 years ago but it settled these kind of discussions.

Now GM first and foremost feeds the assembly lines and back before thin wall casting was applied to the SBC lots of people built 302’s out of 283 and 307 blocks, and even the factory is said to have made some 327’s on this block. But that takes a eight inch over bore, try that on thin wall block! Neither 283’s nor 307’s got 4 bolt mains. Few factory 302’s got 4 bolt mains (only1969). Rumor mill says there were no 4 bolt main 4 inch bore 327’s, but there are other persistent rumors that some were built as to whether they ever got to line production is unknown and probably unlikely.

All I can say is I had a cross bolt Ford 390 which the popular literature says never existed, yet there it was. By this I don’t mean a destroked 427 which was a popular race team build back in the day, several NASCAR Fords advertising a 427 under the hood actually ran with a 3.5 inch stroke crank for a wild big bore 394 inch engine.

If this has a code on the right front pad it might offer some idea of where this was installed originally.

They also make a lot of customized industrial and marine engines and back then those COPO versions that dealers could order up, so there was a lot of crazy going on.

Bogie

 

[Gusjohns]

Where’s the pic of the casting number?
And the suffix code pad?

Where’s the pic of the casting number?
And the suffix code pad?

 

[Gusjohns]

Possible that this is a 307 block that was bored to 4" and a 4 bolt conversion? Interested to know if there is enough meat for a clean up hone or rebore.

 

[BogiesAnnex1]

The HK suffix on the engine build code says this is a 68 327 or a 60 350. The stamped code is the definitive answer so I for one an notating my notes.

If it’s 327 it will stroke at 3.25 inches if a 350 that will measure 3.48 inch.

The long series of smaller stamped code is the partial VIN that if you can crack it will tell what vehicle the engine mated with.

Thanks you made us all a little smarter.

Bogie

 

[cozwurth]

Shouldn't there be something to index the main caps? Looks like the cap is just sitting on the main web of the block, not notched in to index it. Or is the index the same on the block, and covered by the extra material on the cap? I'll have to go over to dad's shop and look at mine.

 

[RWENUTS]

HK shows up here.
If it’s a 327 it could be worth a bunch.

Decoding small block Chevy engine suffix codes and stamped numbers DTR - HQ

Decoding small block Chevy engine suffix codes and stamped numbers: DTR - HQ.

nastyz28.com

 

[BogiesAnnex1]

I should have read my previous entry the HK code is 68, 327 as stated but the 60, 350 should read 69, 350.

Bogie

 

[Gusjohns]

Shouldn't there be something to index the main caps? Looks like the cap is just sitting on the main web of the block, not notched in to index it. Or is the index the same on the block, and covered by the extra material on the cap? I'll have to go over to dad's shop and look at mine.

They are notched in, just difficult to see. It appears that this block is a 69 350 4 bolt, a good score as it has original bore