66 BB GM Cam Surprise - NCRS Discussion Boards

66 BB GM Cam Surprise

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  • Peter M.
    Very Frequent User
    • February 1, 1984
    • 361

    66 BB GM Cam Surprise

    We disassembled my friends early 66 427/425 engine for a rebuild. This engine and the car - appear never to have been apart. When we pulled the cam shaft it was original GM issue but not a 143 but a 144 part # which is a 1965 396/425 cam. When we compared the specs to the 1966 427/425 143 unit they were quite different re lift, duration and even valve lash settings. Do you think this was an aberration or GM just used up internal parts inventories i.e. 396 crank, cam etc in the 427 engine.
  • Joe L.
    Beyond Control Poster
    • February 1, 1988
    • 43193

    #2
    Re: 66 BB GM Cam Surprise

    Peter-----

    The GM #3863144 was the CASTING number used for the GM PART #3863143 camshaft. This camshaft was used for BOTH the 1965 L-78 and 1966 L-72. Although some publications show different camshaft specs for the 2 different years, I believe that this is in error OR the specs were reported differently for the 2 different years. The camshafts, themselves, are the same. For one thing, GM camshafts of the same part number COULD NOT have different specifications. And. as far as I know, the GM casting #3863144 was used ONLY for the GM #3863143 camshaft.
    In Appreciation of John Hinckley

    Comment

    • Peter M.
      Very Frequent User
      • February 1, 1984
      • 361

      #3
      Re: 66 BB GM Cam Surprise

      Joe - The 144 I refer to is stamped in on the face of the rear of the cam - it reads 3144 - there is an H stamped as well. I can not find a full casting number but I can read a cast " GM 9 " between the 4th and the rear bearing journals. There appears to be a dab of green paint as well.

      Comment

      • Bill W.
        Extremely Frequent Poster
        • March 1, 1980
        • 2000

        #4
        Re: 66 BB GM Cam Surprise

        I think they had different specs. because they used different settings .

        Comment

        • Joe L.
          Beyond Control Poster
          • February 1, 1988
          • 43193

          #5
          Re: 66 BB GM Cam Surprise

          Peter------

          I can tell you this, for sure: there NEVER was a FINISHED camshaft of GM PART #3863144. Such a part NEVER existed.

          The difference in the valve lash settings for 65 L-78 and 1966 L-72 may or may not account for the difference in the REPORTED specifications of the camshaft. The camshafts, themselves, were the same.
          In Appreciation of John Hinckley

          Comment

          • Duke W.
            Beyond Control Poster
            • January 1, 1993
            • 15610

            #6
            Re: 66 BB GM Cam Surprise

            Gimme a cam, any cam, an I can come up with an infinite number of specification sets for it, and GM, to a lesser degree did the same. The problem with GM specs when it comes to timing points, duration, and centerlines is that they measured them in different ways as there were no cam specification standards when our vintage cams were developed.

            For example the "30-30" originally had a duration spec of 346 degrees. Now do you really thing that a cam with this much duration will work in anything approaching a street engine. Hardly!

            The Duntov cam events were specified at the "lash points" - the points were all the clearance is taken up with the valve set to OEM clearance spec and a 1.5:1 rocker arm and the duration is 287. The 30-30 cam was specified at some lift above the base circle, but GM never specified what is was and that 346 degrees duration spec includes a lot of the clearance ramps, but it's impossible to compare to any other cam. Later GM published different specs for the 30-30 cam, but they are just as confusing.

            Further confounding the situation is that some GM cams like the 30-30 and LT-1 have asymmetrical lobes so the "centerline" and the "point of maximum lift" are not the same, and finally, the rocker arm ratio is not really 1.5:1, but starts at about 1.37:1 at the lash points and maxes out at about 1.44:1 at maximum lift.

            The above also applies to the big block, but I don't know the details because I've owned a BB and never took the detailed measurements of a BB that one needs to sort out the valve timing and rocker geometry.

            A current SAE standard calls for duration to be measured at .006" VALVE lift, and this is what most aftermarket grinders use for "advertised duration", but then they use a 1.5:1 rocker ratio to get that .006" valve lift, so their duration numbers are in error due to the variance of actual rocker arm geometry.

            About the only consistent GM specification is lobe lift, and this is the maximum height of the lobe above the base circle including the ramps. It's specified in service manuals. The casting number and lobe lift are the only way to identify the cams, but in order to characterize them for comparison to other cams, you have to take a lift-crank angle diagram so you can determine actual timing points that can be compared to other cams.

            Duke

            Comment

            • Peter M.
              Very Frequent User
              • February 1, 1984
              • 361

              #7
              Re: 66 BB GM Cam Surprise

              Joe
              This is getting intetesting - I can email you super detailed pictures of this Cam if you are intestested to take a look. As mentioned - it has GM trademark and a 9 representing "equipment number" cast on the cam, has factory grooved rear oil journal and is clearly stamped with 3144 numbers.

              Comment

              • Joe L.
                Beyond Control Poster
                • February 1, 1988
                • 43193

                #8
                Re: 66 BB GM Cam Surprise

                Peter-----

                I don't think that the photo will help much; I'm pretty familiar with the configuration which you describe. Here's what I believe happened:

                In general, GM camshafts were/are ground from specific camshaft cores. These cores have a specific casting number which also serves to identify the FINISHED camshaft part number since, as I mentioned previously, usually only 1 finished camshaft part number is ground from a particular core. The reason for this is that machining operations are minimized if the camshaft core is cast very close to its final dimensions and configuration. In today's world of "lean manufacturing techniques" this is called "near-net-shape" casting or forging. In days of yore, they didn't call it this, but the principle was the same. High volume manuafacturing, as for OEM engine camshafts, is vastly more cost-efficient and productive if the machining operations necessary to finish the camshaft are minimized.

                Sometimes, for a variety of possible reasons, camshafts may be ground from a "generic" core. These cores are usually specific as to basic engine configuration (e.g. big block), but the as-cast lobes may be oversize and allow for many different lobe configurations to be ground from the same core. Reasons for this might include a shortage of specific cores or a low production camshaft. In 1965 and 1966, the 3863143 camshafts were likely very low production pieces in the context of GMs engine component operations. So, this COULD have been the reason for the use of "generic" cores, at least some of the time.

                In any event, since these camshafts contain no identifying casting number (or, if they do, this "generic" number is likely ground off in the machining operations to avoid confusion), the normal casting number (and camshaft ID number) for the camshaft is stamped into the end of the camshaft for ID purposes. That's how I believe that yours and other camshafts acquire these stamped in numbers. In your case, the "3144" staming means the same thing as another camshaft which has these numbers (or the full 3863143)cast between the journals. As I say, though, the 3863144 always identifies a GM PART #3863143 camshaft. I can find NO information that any other camshsaft besides a GM #3863143 was used for 1965 L-78 engines. Furthermore, as I also mentioned, it is just NOT possible that the 3863143 camshaft was produced with different specifications, depending upon year. If that had been done, I'm quite certain that a different part number would have been assigned.

                By the way, most aftermarket camshaft manufacturers who grind a large number of different camshaft configurations find it much more efficient, for their purposes, to grind camshafts from "generic" cores. For their purposes, having specific "near-net-shape" castings produced for each grind would be far more costly than the extra machining required to manufacture camshafts from "generic" cores. That's why aftermarket camshafts usually have the camshaft ID stamped into the end in the same manner as the GM cam you are looking at.
                In Appreciation of John Hinckley

                Comment

                • Clem Z.
                  Expired
                  • January 1, 2006
                  • 9427

                  #9
                  Re: 66 BB GM Cam Surprise

                  the specs i have for the 65 396 corvette cam,lash in .012,ex .018,in open 61 degrees 9 minutes btc,in closes 107 degrees 13 minutes 20 seconds abc,lift .497, dur 348 degrees 22 minutes 20 seconds. ex open 109 degrees 9 minutes bbc,ex closes 66 degrees 16 minutes 40 seconds atc,lift .503,dur 348 degrees 25 minutes 40 seconds,overlap 127 degrees 25 minutes 40 seconds,part # 3863144. specs for 1966 427 425 hp corvette cam,intake lash .024,ex .028, in open 54 btc,in close 102 abc,lift .5197,dur 336,ex open 102 bbc,ex close 54 atc,lift .5197,dur 336,overlap 108,part # 3863143. anyone with a computer cam program may be able to plug in the numbers and see how they compare if you change the valve lash

                  Comment

                  • Joe L.
                    Beyond Control Poster
                    • February 1, 1988
                    • 43193

                    #10
                    Re: 66 BB GM Cam Surprise

                    clem-----

                    I don't know where they came up with specs for a GM #3863144 camshaft; there never was any such FINISHED camshaft. GM #3863144 was the CASTING number for a raw, camshaft core which was used to produce the GM #3863143 FINISHED camshaft.

                    By the same token, IF GM #3863144 number which appeared on the part had been a part number for a finished camshaft, then the GM #3863143 must never have existed. I don't believe that you'll ever find a GM camshaft with the number "3863143" stamped or embossed on it anywhere.

                    I really believe that the differences in the specs for the 1965 L-78 camshaft and the 1966 L-72 camshaft had to do with the phenomenon that Duke was describing. Whether it related to just the valve lash differences or whether it related to some other and different way of measuring camshaft specs that was used for 1965 and 1966, I don't know.

                    Another difference in specs will be found between the GM #3863143 camshaft and the GM #3904362. However, I believe that the 3863143 and the 3904362 have, in fact, identical specs. The difference is that the 3863143 had the rear journal grooved as required for 65-66 engines. The 3904362, released for the 1967 model year, lacked the groove, since it was not necessary for 1967 engines. Somehow or another, the "specing system" used for the 2 camshafts was different so they received different specs, even though they were the same, in fact.

                    For many years, GM sold only the 3863143 to SERVICE all 65-71 SHP applications since this was the camshaft that would work perfectly well with either early or late engines and avoid "problems" created by the use of a non-grooved camshaft in an early engine. Later, the 3863143 was discontinued from SERVICE and was replaced by the GM #3904362. I don't know if the SERVICE 3904362 cams were modified to have the groove, or not.
                    In Appreciation of John Hinckley

                    Comment

                    • Bill W.
                      Extremely Frequent Poster
                      • March 1, 1980
                      • 2000

                      #11
                      Re: 66 BB GM Cam Surprise

                      Joe I looked at my orig.L78 cam & it is cast 144 . I have a new 4362 it does not have a grove but comes with a spec sheet to machine one. it does not have a 144 cast. the lobe size is close to the 144. Bill

                      Comment

                      • Clem Z.
                        Expired
                        • January 1, 2006
                        • 9427

                        #12
                        Re: 66 BB GM Cam Surprise

                        joe every GM BBC cam i ever looked at had a number stamped on the back of the rear cam journal and this 144 stamp my have been the cam # in 65 but the over the counter replacement part# was 143. i have a list of old BBC cams here one was stamped 605,do you have listing for a BBC cam ending with that number?

                        Comment

                        • Clem Z.
                          Expired
                          • January 1, 2006
                          • 9427

                          #13
                          Re: 66 BB GM Cam Surprise

                          bill,is there a # stamped on the back of the rear cam journal of either cam

                          Comment

                          • Joe L.
                            Beyond Control Poster
                            • February 1, 1988
                            • 43193

                            #14
                            Re: 66 BB GM Cam Surprise

                            clem-----

                            I don't doubt, at all, that GM camshafts may have numbers stamped on the end of the journal. What the significance of the numbers may be is another story, though. In the case of the camshaft originally the subject of this thread, from what was reported it did not carry the usual camshaft ID number cast between the lobes. However, it did carry the "3144" number stamped on the end of the journal. I interpret this to be a derivative of the camshaft ID number used for the GM #3863143 camshaft. That ID number, when cast between the lobes, is 3863144 or 3144. I can find no record, whatsoever, of a FINISHED camshaft part number of 3863144. However, as I say, we do know, for sure, that 3863144 was the ID number AND the casting number for the GM #3863143 FINISHED camshaft. That it could also be the PART number for a FINISHED camshaft is a virtual impossibility within the GM parts system. Plus, as I say, I can find absolutely no record of a finished camshaft of part #3863144 either used in PRODUCTION or available in SERVICE.

                            Also, I can find no record of any big block camshaft which either used an ID number ending in "605" or any finished camshaft PART # ending in "605". It's possible that it was truck-only or industrial engine-only camshaft as I may not have records of such pieces. However, I think that it's more likely that it has some other significance and is not related to a part number or camshaft ID number. I think that many of these cam-end stampings have significance other than a cam part number derivative or a cam ID number. However, I feel pretty confident that the "3144" stamped on the end of the above-referenced camshaft is a reference to the camshaft ID number which is otherwise absent on this particular camshaft.
                            In Appreciation of John Hinckley

                            Comment

                            • Bill W.
                              Extremely Frequent Poster
                              • March 1, 1980
                              • 2000

                              #15
                              Re: 66 BB GM Cam Surprise

                              no both ends are machined with no #s are stamps

                              Comment

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