When Did Broach Marks Stop? - NCRS Discussion Boards

When Did Broach Marks Stop?

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  • Terry M.
    Beyond Control Poster
    • September 30, 1980
    • 15601

    #16
    Re: When Did Broach Marks Stop?

    When the Small Block was introduced by Chevrolet the broach machine (Made by what was then called Cincinnati Milling Machine) was heralded in a press release for the flat plane of the surface as well as the surface finish; as a means of ensuring sealing between the cylinder case and the head surface. What we evaluate as "broach marks" are the surface finish referred to in that release. I wish I had access to that release, but I do not have a copy. I have seen it, but can't remember where or when. Perhaps someone with access to the Heritage Center may be able to hunt it down.

    As an ancillary question: How were the 6-cylinder stamped surfaces machined? Not being part of a sealing surface makes the quality of the surface is less relevant, but I still have to ask.
    Terry

    Comment

    • Cecil L.
      Very Frequent User
      • May 31, 1980
      • 449

      #17
      Re: When Did Broach Marks Stop?

      The W (348/409) blocks wouldn't fit the broaching machines due to the 74 degree deck angle so they were milled with circular marks.

      Comment

      • Mike M.
        NCRS Past President
        • May 31, 1974
        • 8385

        #18
        Re: When Did Broach Marks Stop?

        Terry: u have a pm. merry Christmas, mike

        Comment

        • Patrick B.
          Extremely Frequent Poster
          • August 31, 1985
          • 1995

          #19
          Re: When Did Broach Marks Stop?

          Originally posted by Steven Brohard (5759)
          and the 1969 aluminum blocks, how were they done?

          Comment

          • Dave P.
            Very Frequent User
            • June 30, 1991
            • 192

            #20
            Re: When Did Broach Marks Stop?

            This is an early 2nd gen LT1, but Flint was still using the horizontal surfacing machine in October 1991. (Open pic in new tab and Ctrl + + to expand). The broach marks are a little faint, but they are definitely there.

            Another production change around the same time is that the blocks were painted prior to machining. All machined surfaces are paint free.

            IMG_4488.jpg

            Comment

            • Mark F.
              Extremely Frequent Poster
              • July 31, 1998
              • 1527

              #21
              Re: When Did Broach Marks Stop?

              Originally posted by Dave Perry (19643)
              This is an early 2nd gen LT1, but Flint was still using the horizontal surfacing machine in October 1991. (Open pic in new tab and Ctrl + + to expand). The broach marks are a little faint, but they are definitely there.

              Another production change around the same time is that the blocks were painted prior to machining. All machined surfaces are paint free.
              Hi Dave,

              Seems a very odd automotive engine plant production sequence to me (painting a casting as large as this before machining).
              Yes, I know smaller parts were done like that (caliper halves; master cylinders; etc.)

              I assume the cutting "oils" (really, fluids w/ many chemical additives BTW) were all water-based at that time, but even taking that into account, after those machining steps the block would have to be cleaned somehow to remove the residual cutting fluids off the engine block paint, right ?

              Any idea why this sequence was changed this way compared to how it was done previously ?
              thx,
              Mark

              Comment

              • Michael W.
                Infrequent User
                • July 14, 2020
                • 9

                #22
                Re: When Did Broach Marks Stop?

                broach.jpgNot a very good photo, but here's the broaching tool.

                Comment

                • Harry S.
                  Extremely Frequent Poster
                  • July 31, 2002
                  • 5302

                  #23
                  Re: When Did Broach Marks Stop?

                  Better picture and read.

                  https://www.forums.ncrs.org/showthre...broach+machine


                  Comment

                  • Owen L.
                    Very Frequent User
                    • September 30, 1991
                    • 868

                    #24
                    Re: When Did Broach Marks Stop?

                    BlockBroach.jpg

                    It appears to me the left-hand broaches are the oil pan and crank mains while the right-hand broaches are for the cylinder head deck and intake?

                    As I understand broaching (of keyways), it's a set of progressively deeper cuts to yield the final dimension. If the block enters from the foreground end of the pic and is pushed to the background, was it finished at this point or was there another set of broaches like those shown that the block was moved under?

                    How likely is it that the engines before and after mine ended up in Corvettes? The broach marks within a sequence of blocks should have the same sort of "fingerprint", yes?

                    Comment

                    • Terry M.
                      Beyond Control Poster
                      • September 30, 1980
                      • 15601

                      #25
                      Re: When Did Broach Marks Stop?

                      Originally posted by Harry Sadlock (38513)
                      Nice search Harry. Well done.

                      I almost began to weep at the names of those posters. A large number of my best friends posted there. I tried to count those who are deceased, but couldn't get to all of them. It is a shame the skill and knowledge we have lost.
                      Terry

                      Comment

                      • Terry M.
                        Beyond Control Poster
                        • September 30, 1980
                        • 15601

                        #26
                        Re: When Did Broach Marks Stop?

                        Originally posted by Owen Lowe (20119)
                        [ATTACH=CONFIG]124607[/ATTACH]

                        It appears to me the left-hand broaches are the oil pan and crank mains while the right-hand broaches are for the cylinder head deck and intake?
                        Yes Owen your observation is correct.

                        As I understand broaching (of keyways), it's a set of progressively deeper cuts to yield the final dimension. If the block enters from the foreground end of the pic and is pushed to the background, was it finished at this point or was there another set of broaches like those shown that the block was moved under?
                        Regardless the posts on the linked thread the Cincinnati built machines I saw at both Flint and Tonawanda (and I didn't see all the broach machines at either location) locked the cylinder cases and the broaches moved. There is not enough perspective in the photo shown for me to determine whether we are looking at the finish cutters or the rough cutters. Someone who has more time and experience in these kinds of production environment might be better able to answer your question.

                        How likely is it that the engines before and after mine ended up in Corvettes? The broach marks within a sequence of blocks should have the same sort of "fingerprint", yes?
                        The machining and assembly transfer lines had some sequence to them, but there were numerous operations that resulted in a loss of this sequence. There was no effort to retain the sequence. The steel stamp operation is more sequential but there is no sequence to the racking and shipping of the completed engine assemblies. There is also no sequence to the engine install at St Louis (or Bowling Green). You are better off buying a lottery ticket. ;-)

                        See my comments in the quote above. I hope doing it this way is clear. I tried to make my remarks a different color, but I failed. If one of you high tech folks can do that for me it might be helpful.
                        Last edited by Gary C.; December 23, 2024, 07:58 AM. Reason: changed Terry MC's text to blue
                        Terry

                        Comment

                        • Dave P.
                          Very Frequent User
                          • June 30, 1991
                          • 192

                          #27
                          Re: When Did Broach Marks Stop?

                          Originally posted by Mark Francis (30800)
                          Seems a very odd automotive engine plant production sequence to me (painting a casting as large as this before machining).

                          Any idea why this sequence was changed this way compared to how it was done previously ?
                          Look at the pad on my Oct 1991 LT1 again. (The 'black' is the original prior to cleaning painted surface.) The surface outboard of the pad is lower than the finished deck height, so the paint on that area remained after surfacing. It's apparent that the pad and deck wasn't masked prior to painting, it was machined after paint was applied.

                          It may be "odd", but my observations on iron V-configuration blocks (V6-90, Mark V, Mark VI, my 92 LT1) from the early '90s onward show that this was what they did. No machined pad or surface is painted. There is no paint in any threaded hole. The pan and timing cover gaskets have no paint on the exposed surface. The oil pans and timing covers are a different gloss of paint or plastic (1996 onward). The pan and timing cover fasteners are black phos, but not painted.

                          I have not a clue as to why the engine paint process was changed, but here's some thoughts: Perhaps not wanting to have to mask aluminum components like cyl heads, valve covers and plastic timing chain covers? Keep paint out of threaded holes? Not have to elevate completed engines for paint application to the bottom of oil pans?

                          Comment

                          • Terry M.
                            Beyond Control Poster
                            • September 30, 1980
                            • 15601

                            #28
                            Re: When Did Broach Marks Stop?

                            Originally posted by Dave Perry (19643)

                            I have not a clue as to why the engine paint process was changed, but here's some thoughts: Perhaps not wanting to have to mask aluminum components like cyl heads, valve covers and plastic timing chain covers? Keep paint out of threaded holes? Not have to elevate completed engines for paint application to the bottom of oil pans?
                            DAVE
                            I asked that question.
                            They wanted to get the emissions from painting out of the engine assembly plant. The painting process is outsourced. I don't know if the casting plant paints the cases or if there is a stop along the way between the casting plant and the assembly plant.
                            Last edited by Terry M.; December 23, 2024, 11:24 PM. Reason: typo correrction
                            Terry

                            Comment

                            • Dave P.
                              Very Frequent User
                              • June 30, 1991
                              • 192

                              #29
                              Re: When Did Broach Marks Stop?

                              Originally posted by Terry McManmon (3966)
                              DASVE
                              I don't know if the casting plant paints the cases or if there is a stop along the way between the casting plant and the assembly plant.
                              Thank You. Now I have a clue. Where were the cases machined? Casting plant, Assembly plant, or an intermediary "Machining plant"? Regardless, they were painted before machining.

                              Another trivia tid-bit which sometimes comes up in discussion: Are the engine and accessory fasteners SAE or Metric? I forget where I read this (perhaps on here?), but my empirical observations concur. If the threaded hole is in the case, cyl head or some other component (intake manifold) that was threaded in the engine plant, it is SAE. If the threaded hole is in an accessory or bracket that was not machined in the engine plant, it is Metric. I'm pretty sure this convention held to the end of production of the V8 and 90 deg V6 at both Flint and Tonawanda. (Disclaimer: The 8.1 was produced at Tonawanda. The 8.1 resembles a Gen VI big block, but there are a lot of nuances and differences between an 8.1 and a 7.4. The 8.1 could be Metric, but I don't know for sure.)

                              When working under the hood of any '80s - '90s era GM with a V8 or V6/90, keeping this in mind helps to select the correct socket or wrench from the roll-away.

                              Comment

                              • Terry M.
                                Beyond Control Poster
                                • September 30, 1980
                                • 15601

                                #30
                                Re: When Did Broach Marks Stop?

                                Originally posted by Dave Perry (19643)
                                Thank You. Now I have a clue. Where were the cases machined? Casting plant, Assembly plant, or an intermediary "Machining plant"? Regardless, they were painted before machining.
                                Dave
                                I can only speak to iron blocks. The ones that were painted after assembly were shipped to Flint as raw castings and machined and cleaned at Flint Engine Assembly.

                                I would guess those that were painted before machining were cleaned before painting. I know that painting was outsourced from Flint. I failed to ask where they were painted. I do have a means of asking these questions, but I am loth to bother my contact on a family Holiday week. I'll try next week and post the results.

                                Merry Christmas to one and all
                                Terry

                                Comment

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