327 Engine Questions

[Joe Fisher]

I just aquired a 327 short block. The casting number is 3782870, date code is L112. But the front pad has no numbers stamped on it. The deck has no milling marks and appears to be untouched. Could this be a replacement block, and did they come with blank pads? If this block was restamped with the correct numbers, would it pass judging? Also the crank number is 3782680, pistons 3795337 and the balancer has R42, 6966, 01M4. Can you help me identify these items.

[Joe L.]

Re: 327 Engine Questions

Joe-----

The block which you have is likely a replacement block that was purchased "over-the-counter" either as a bare, fitted, or complete short block. In general, these blocks do not have any numbers stamped upon the engine pad. However, the engine pad is a "virgin" pad (unless the engine was previously decked) and is exactly the same as the pad which the engine and vehicle assembly plants stamped on the pad for PRODUCTION engines. Presumably, with the correct stamping equipment, one could duplicate an original stamping. Just how detectable and/or acceptable that such an effort might be I'll leave to others.

Your crankshaft is a forged steel unit as originally used in 62-67 Corvette and other Chevrolet 327 cid applications except special high performance and FI. This casting was known by several part numbers, the last one being GM #3889304.

I believe that your casting #3795337 pistons are GM part #3799491. These were cast aluminum pistons used for many 62-68 327 cid applications except special high performance. If I am correct, they should be of "flat-top" configuration with 4 eye-brow shaped valve reliefs. With 64 cc cylinder heads and stock, shim-type head gaskets, these pistons will produce a compression ratio of about 10:1.

I can't ID the balancer based upon the information which you've provided. However, I expect that it's a either a GM #3861970 which is 4-1/2" in diameter or a GM #3896903 or 904 which are 6-1/8" diameter and 3/4" thick.

[Joe Fisher]

Re: 327 Engine Questions

Joe, Thanks for the info. The pistons have a raised dome, not flat. They appear to be forged by the looks of the underside of the pistons.

[Joe L.]

Re: 327 Engine Questions

Joe-----

If the pistons are domed and are original GM pistons as evidenced by the casting numbers, then they must be the 62-68 special high performance pistons used with 340, 350, 360, 365, and 375 hp engines. Those are the only pistons with GM casting numbers that are of the configuration which you describe. And, as you surmise, those are forged pistons. In fact, the 1962 Corvette with 340 and 360 hp engines were the first GM small blocks to use forged pistons; all earlier 283 engines, regardless of horsepower rating, used cast aluminum pistons.

There were several iterations of the SHP 327 pistons used from 62-68, but the differences are relatively minor and, as far as I know, all are interchangeable.

To be honest, I'm a little surprised that your engine has these pistons given the crankshaft with which it is equipped; I don't think that these pistons were ever used with that particular crankshaft forging. So, that may mean that this engine was built up from a bare or fitted block using other GM parts.

By the way, what is the size of the balancer which is on the engine? This part would have been purchased seperately and installed since short block assemblies which GM sold in those years were rarely supplied with balancers "out-of-the-crate".