Questions about casting/machining on blocks at engine plants - Chevelle Tech
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post #1 of 16 (permalink) Old Apr 19th, 17, 3:14 PM Thread Starter
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Questions about casting/machining on blocks at engine plants

Over the years I've noticed that first generation small blocks which are the same (327, 350, SB400, etc) do not always have the same machining processes done to them. After casting, and after the molds are remove, how did the line workers know which holes to drill/tap and not to drill/tap on the SAME KIND OF BLOCK? For example, I just recently taken notice on some of my SB400 blocks that some holes are drilled/tapped and some are not-------------------and this is on blocks which have the same casting numbers! Below are 400 blocks which have the bosses cast for the clutch Z-bar (same on 327 and 350 blocks), but some are not drilled/tapped and some are not. What determines this? All small blocks also have the bosses at the front of the block, which were ORIGINALLY for attachment of 55-57 Chevy front engine mounts (ONLY years used for mounting up front). All subsequent blocks have these bosses, but some are drilled/tapped and some are not. SOME later blocks used these holes for mounting accessories such as pwr str pump brackets. ALL blocks have the boss for an oil pressure passage in the top-front of the block, but some have no hole drilled/tapped and some have the threaded hole, but have a plug installed. Any comments on this? Two SB400 blocks with no holes for the Z-bar stud. Two SB400 blocks with the holes drilled/tapped. This block had NO HOLES in the bosses on the left side, which I drilled/tapped for a pwr str pump bracket (the holes in the right bosses were already there). This is the front oil passage I referred to. All small blocks have the boss for the passage. Some blocks do not have the passage drilled from the front of the block down into the center oil galley and some do, and have 1/8in pipe threads and then a plug installed. On all of my engines that don't have the passage drilled/tapped, I do it and install an oil pressure gauge. I even did it on the 455 Olds engine in my Cutlass. Again, my question, why were some holes drilled/tapped on the same engines (even with the same casting number) and some not? How would the engine plant line workers know which to drill and which not to drill?

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post #2 of 16 (permalink) Old Apr 19th, 17, 11:49 PM
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Re: Questions about casting/machining on blocks at engine plants

It would be down to production planning just like some blocks are drilled (and machined) for 4-bolt mains vs 2-bolt mains.

As an aside, all 4-bolt blocks (small block) that I have seen have had the front oil port above the timing cover drilled and tapped with a plug in it. I have never seen a large-journal 2-bolt with that port present (small-journal - yes, large journal - no). Often a good visual clue on a 1970's motor.
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post #3 of 16 (permalink) Old Apr 20th, 17, 1:09 AM
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Re: Questions about casting/machining on blocks at engine plants

400s were not sold with manual trans that I know of, so probably not normally drilled. Production runs at a plant are probably the key.

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post #4 of 16 (permalink) Old Apr 20th, 17, 6:56 AM
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Re: Questions about casting/machining on blocks at engine plants

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Originally Posted by chrisstandring View Post
I have never seen a large-journal 2-bolt with that port present
Hate to burst your bubble but I have two of them sitting here in front of me right now.

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post #5 of 16 (permalink) Old Apr 20th, 17, 7:57 AM
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Re: Questions about casting/machining on blocks at engine plants

I believe the 400 small block could be had in 1970 with a four speed stick.

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post #6 of 16 (permalink) Old Apr 20th, 17, 8:05 AM
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Re: Questions about casting/machining on blocks at engine plants

Pretty sure the 400 small block was available in trucks with standard transmissions. The one I have on the stand was out of a mid 70's blazer and the boss needs drilled. Jim

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post #7 of 16 (permalink) Old Apr 20th, 17, 6:48 PM Thread Starter
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Re: Questions about casting/machining on blocks at engine plants

Look at the 2nd and 3rd pictures. On the top of the bell housing flange in the 2nd picture, the boss is NOT drilled/tapped for a spark plug wire bracket, but it is on the 3rd picture. Just another example of some blocks with holes and some not. Now, how would the engine plant line workers know that one block would get brackets for spark plug wires and another block would not?

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post #8 of 16 (permalink) Old Apr 20th, 17, 6:50 PM Thread Starter
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Re: Questions about casting/machining on blocks at engine plants

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Originally Posted by paul bell View Post
I believe the 400 small block could be had in 1970 with a four speed stick.
Many years ago, I saw a very plain 70 or 71 Monte with a SB400 and 4sp in Enid, OK.

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post #9 of 16 (permalink) Old Apr 20th, 17, 7:02 PM Thread Starter
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Re: Questions about casting/machining on blocks at engine plants

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Pretty sure the 400 small block was available in trucks with standard transmissions. The one I have on the stand was out of a mid 70's blazer and the boss needs drilled. Jim
I have seen a couple. Also, in Chevy parts books, they used to list a manual flywheel for a SB400. But, it's super easy to make your own using EITHER a 454 flywheel, or, a neutral balance 168 teeth manual flywheel. When having your machine shop balance the rotating assembly, the needed metal can be removed by either drilling or milling as needed for balance. I've had this done to 2 engines using a neutral balance flywheel and holes were drilled to remove metal. Below is a neutral balance 153 teeth flywheel which is on the 383 that I built for the 51 Chevy. You can see where metal was drilled for balance.

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post #10 of 16 (permalink) Old Apr 20th, 17, 7:34 PM
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Re: Questions about casting/machining on blocks at engine plants

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Originally Posted by paul bell View Post
I believe the 400 small block could be had in 1970 with a four speed stick.
1970-only, Monte Carlo was offered with an M20 Muncie. In 1971 in theory you could get a Caprice or Kingwsood Estate with a manual 400 (SAE specs call for a Saginaw, yikes!) I have serious doubts that any were built of the latter.
The 400 made it to the G (Chevyvan) & K series (4x4 models) trucks for 1975 through 1980. I have never seen an availability chart that shows the light duty trucks to be offered with a 400 / manual drivetrain, just the hydramatic.

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post #11 of 16 (permalink) Old Apr 20th, 17, 8:11 PM
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Re: Questions about casting/machining on blocks at engine plants

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Originally Posted by DZAUTO View Post
I have seen a couple. Also, in Chevy parts books, they used to list a manual flywheel for a SB400. But, it's super easy to make your own using EITHER a 454 flywheel, or, a neutral balance 168 teeth manual flywheel. When having your machine shop balance the rotating assembly, the needed metal can be removed by either drilling or milling as needed for balance. I've had this done to 2 engines using a neutral balance flywheel and holes were drilled to remove metal. Below is a neutral balance 153 teeth flywheel which is on the 383 that I built for the 51 Chevy. You can see where metal was drilled for balance.

The problem with doing it that way is that now you have a flywheel / rotating assembly that are married to each other.


The correct way to do it is to match your stick shift flywheel to a factory 400 flywheel or flexplate and then use it when balancing the assembly. That way if you ever need to replace the flywheel any flywheel or flexplate meant for a 400 will work.

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post #12 of 16 (permalink) Old Apr 21st, 17, 12:26 AM
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Re: Questions about casting/machining on blocks at engine plants

My 400 sb had a hole for the cross shaft ball stud, engine was original to the car and pulled from a 72 Impala with an auto trans.

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post #13 of 16 (permalink) Old Apr 21st, 17, 12:49 PM Thread Starter
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Re: Questions about casting/machining on blocks at engine plants

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The problem with doing it that way is that now you have a flywheel / rotating assembly that are married to each other.


The correct way to do it is to match your stick shift flywheel to a factory 400 flywheel or flexplate and then use it when balancing the assembly. That way if you ever need to replace the flywheel any flywheel or flexplate meant for a 400 will work.
Bill, That is exactly correct---------------------------provided you have a 400 flywheel available. In the case of the 153 teeth flywheel that I used for the 383 in the 51, there is no such thing as a 153 teeth flywheel for a SB400. Also, neutral balance 168 teeth flywheels are much more readily available than EXternal balance flywheels. I've never been lucky enough to run across a 400 specific flywheel, so I've used 454 flywheels for my 400s and had the balancing done as needed. Yep, I realize that the sum of the parts makes the rotating assembly unique and specific to that engine, but then again, I'm not tearing them down for a rebuild frequently. So I just roll the dice and have everything balanced together.

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post #14 of 16 (permalink) Old Apr 21st, 17, 6:28 PM
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On the "to drill, or not to drill question"....

I would suspect that each finish-machined block had a part number associated with it, and that the same casting was used for several finished parts. Machine shop likely had a drawing associated with the finished block part number that showed them exactly what to drill and not drill.
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post #15 of 16 (permalink) Old Apr 21st, 17, 6:31 PM
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Another thing... it costs money to drill and tap holes. I'm sure someone looked at this and eliminated unnecessary (for the application) holes as a way to achieve cost reduction goals. Every penny counts in a production environment, and nobody worried about what hot rodders might do with the block later.
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