We are currently haveing a discussion around 2 and 4 bolt mains and how to identify them. I have also found an interesting thread ona similar topic in "the other forum"

Pierre Lafontaine "Chevrolet Small Block V-8 ID Guide" - says:
One of the most sought-after engines is the 350ci four-bolt. In 1968, when the 350ci was introduced, the four-bolt was born. Thid block is m0ost desirable for any high-performance application. This block has been used in trucks, Z-28s (Camaros), Corvettes and marine applications. There are a few identifying marks on the block that are apparent from the outside, even when the engine is completely installed. The only block to have the oil pressure take-off drilled and tapped at the front of the block is the four-bolt 350ci. The exact location of this pressure feed is just above the timing-cover slightly to the passenger side. The pressure feed has been used on trucks to supply oil pressure to asseccories, such as power take-off. On the Corvettes, it has been used for the oil pressure sensor (GM felt there was no sufficient room at the back for the sending unit). In most cases, the 1/8in pipe thread hole is plugged with a square head pipe plug. Although having a block with this plug in the front almost guarantees it of being a four-bolt, many four-bolts were not drilled.

Alan L. Colvin "Corvette by the numbers 1955-82" writes mainly the same.

What about this plug in the 327´s blocks....we know these are 2 bolts....when did the General introduce these oil pressure drillings ? Was it also in the smaller and older blocks like the 283 ?

Creates a little confusion....can someone enlighten us ?
:cheers:


[Modified by Mikey1, 11:05 AM 9/11/2003]

 

The 1/8" NPT square-head pipe plug at 11 o'clock just above the timing cover has nothing whatsoever to do with any oil pressure fittings, nor does it have anything to do with 2-bolt vs. 4-bolt configuration. Flint Engine had a different machining process than Tonawanda, and required that hole for gun-drilling an oil passage at the front of the block; the hole was then tapped and the plug was installed. Tonawanda's machining process didn't require the hole, so you won't find it on any Tonawanda blocks.

Urban legends die hard - there are no external indications of any kind that differentiate a 2-bolt from a 4-bolt small-block; the only difference is extra main cap bolt holes in the #2-#3-#4 bulkheads on a 4-bolt - there is no difference at all in the castings - the same castings were used for both - only the machining for the extra six holes was unique. :thumbs:

 

Thanks John !!