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Dwell? Should I Fix?

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  • #16
    I’m a little bit confused, ok a little bit more than normal. If dwell decreases as gap increases, shouldn't the point gap be set at the high end of the range to compensate for a little wear on the point block of a new set? Doesn’t the point gap decrease as the block wears on a new set? Shouldn’t the dwell be at the lower end of the range on a fresh set of points?

    regards,
    Jay

    Comment


    • #17
      Originally posted by IMJ View Post
      I’m a little bit confused, ok a little bit more than normal. If dwell decreases as gap increases, shouldn't the point gap be set at the high end of the range to compensate for a little wear on the point block of a new set? Doesn’t the point gap decrease as the block wears on a new set? Shouldn’t the dwell be at the lower end of the range on a fresh set of points?

      regards,
      Jay
      My humble attempt to describe/explain "dwell"...think of bucket (coil) and a garden hose (your 6 or twelve volt power supply). You are needing to dump a large volume of water (electrical current) quickly. To accomplish this, you take your garden hose (compare that to the electrical current... the primary electrical circuit flowing through your points) and fill the bucket. The time it takes to fill that bucket, is your "dwell" time. Once you have the required water in the bucket (your coil)...you put down the garden hose (open the points), grab the bucket, and quickly dump the entire volume of its contents!(that fires your spark plug!) If you don't fill the bucket (your coil), the content is less, and probably dumped too soon.

      I like to think of the process of setting the point gap, as a "gross" ballpark setting. Precise setting is possible with a feeler gauge, but a dwell meter is the best way I know of "confirming" the setting. You can't really measure it as "time," but in terms of angle. Since the true time varies with RPM...mechanical angle stays the same, regardless of speed. Thus...DWELL ANGLE.

      "Time," is compensated by (I think) the relationship of a coordinated combination of vacuum advance, centrifugal weights, and carburetor accelerator pump, to adjust in anticipation of demand variations.

      All of the above, may not be completely accurate. Feel free to correct, expand, and expound at will.
      John Clary
      Greer, SC

      SDC member since 1975

      Comment


      • #18
        This has been discussed numerous times on the forum over the years.
        You are correct. The things that 'wear' are (a) the rubbing block, and (b) the point surface itself.
        The point wear will increase the gap (but it is never an 'even' wear).
        The rubbing block wear will decrease the gap (thus increasing the dwell)
        My experience has been that the rubbing block will wear faster than the points will erode.
        So, I always set my dwell on the low range of the suggested dwell range.
        That way the dwell will work it's way up through the suggested range and the tune up will last longer.



        Originally posted by IMJ View Post
        I’m a little bit confused, ok a little bit more than normal. If dwell decreases as gap increases, shouldn't the point gap be set at the high end of the range to compensate for a little wear on the point block of a new set? Doesn’t the point gap decrease as the block wears on a new set? Shouldn’t the dwell be at the lower end of the range on a fresh set of points?

        regards,
        Jay
        HTIH (Hope The Info Helps)

        Jeff


        Get your facts first, and then you can distort them as much as you please. Mark Twain



        Note: SDC# 070190 (and earlier...)

        Comment


        • #19
          I am a true back yard mechanic. A previous vehicle I once owned, a 6 cylinder had an assigned point gap of .018 -.020. I would always set the gap to .020 first then set the timing with a light bulb (static) turn the fan until the light comes on and check the timing mark. I would repeat the process until the timing mark and the light were in line. When the timing was locked up it never had to be touched again. The telltale that the points (dwell) was out of wack would be incipient slight pinging. I would either reset the points back to .020 or replace them. It was usually easier to pull the distributor when replacing the points for this work and therefore the timing would require to be reset. If just resetting the points, the timing did not have to be touched.

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          • #20
            That's how they (used to) set the timing on all the top fuel dragsters and funny cars (even though they had magneto's).
            Very sound method.


            Originally posted by altair View Post
            I am a true back yard mechanic. A previous vehicle I once owned, a 6 cylinder had an assigned point gap of .018 -.020. I would always set the gap to .020 first then set the timing with a light bulb (static) turn the fan until the light comes on and check the timing mark. I would repeat the process until the timing mark and the light were in line. When the timing was locked up it never had to be touched again. The telltale that the points (dwell) was out of wack would be incipient slight pinging. I would either reset the points back to .020 or replace them. It was usually easier to pull the distributor when replacing the points for this work and therefore the timing would require to be reset. If just resetting the points, the timing did not have to be touched.
            HTIH (Hope The Info Helps)

            Jeff


            Get your facts first, and then you can distort them as much as you please. Mark Twain



            Note: SDC# 070190 (and earlier...)

            Comment


            • #21
              I haven't seen any mention of distributor cam lubrication. Be sure to lube the rubbing block to prevent wear, or at least slow it down as much as possible. I like to give the cam a light coating so it doesn't rust from condensation. Also make sure the grease or oil cup is filled with lubrication every so often.

              While on a day tour one guy's distributor seized and broke the tang of the shaft because he wasn't aware of the oil cup on the distributor. Three of use stayed behind to get him back on the road, but it was too late for the tour, so we just drove home.

              Comment


              • #22
                [QUOTE]install a new set and set to the highest recommended dwell to account for wear in of the point block./QUOTE] ???

                [QUOTE][/I’m a little bit confused, ok a little bit more than normal. If dwell decreases as gap increases, shouldn't the point gap be set at the high end of the range to compensate for a little wear on the point block of a new set?]

                [QUOTE]So, I always set my dwell on the low range of the suggested dwell range.
                That way the dwell will work it's way up through the suggested range and the tune up will last longer.

                /QUOTE]
                Last edited by IMJ; 06-23-2016, 04:41 AM.

                Comment


                • #23
                  Yes, you should use a small amount of cam lube to slow the rubbing block wear.
                  If your block wears (faster then the points themselves) then the gap will be decreasing as the block wears.
                  If the gap is decreasing, then the dwell will be increasing.
                  So... If you set the dwell the the low range number, and the dwell will be increasing due to the gap decreasing then your tune up should last longer.



                  [QUOTE=IMJ;997786][QUOTE]install a new set and set to the highest recommended dwell to account for wear in of the point block./QUOTE]

                  [QUOTE][/I’m a little bit confused, ok a little bit more than normal. If dwell decreases as gap increases, shouldn't the point gap be set at the high end of the range to compensate for a little wear on the point block of a new set?]

                  So, I always set my dwell on the low range of the suggested dwell range.
                  That way the dwell will work it's way up through the suggested range and the tune up will last longer.

                  /QUOTE]
                  HTIH (Hope The Info Helps)

                  Jeff


                  Get your facts first, and then you can distort them as much as you please. Mark Twain



                  Note: SDC# 070190 (and earlier...)

                  Comment


                  • #24
                    Just install Pertronix, and forget all the hassle of points. You will still need to put a few drops of oil on the felt beneath the rotor button, and in the outside oiler though, now & then.

                    Comment


                    • #25
                      Correct me if I am wrong, but I always thought that timing effects dwell, but dwell does not affect timing. After reading this tread, I don't think that has been clearly stated. I always set the timing first, then set the dwell, but after a couple of strokes and a seizure, I may be wrong in my memory. The medications I take and rehab has brought me back to 90 percent but sometimes I don't trust my memory.

                      Bob Miles
                      Tucson AZ

                      Comment


                      • #26
                        Originally posted by JoeHall View Post
                        Just install Pertronix, and forget all the hassle of points. You will still need to put a few drops of oil on the felt beneath the rotor button, and in the outside oiler though, now & then.
                        Well...that depends...on the Pertronix working correctly, installed correctly, and the owner understanding it. We've seen several threads of problematic component failure and conversions here. Personally, I have zero experience with a vintage distributor converted to electronic. The SDC member, who comes to my mind, as the "go-to guru" for electronic distributor conversion, is Dave Thibeault. Not only does he modify, service, and sell them, but a "true believer," in his product. So much so, that while talking personally with him at the South Bend Swap meet, he explained the way they operate in clear, understandable terms. In fact, it made so much sense, I was ready to convert all my Studebakers, my 8N Tractor, and a couple of lawn mowers! It was when he gave me a price...that this ol' hillbilly's wide eyed excitement immediately, returned to my natural "cheapo" reality. I decided even the ECM controlled ignition system in my Dodge Ram...all those great features of an electronic system...still couldn't get me the more than six hundred miles home, without enough gas money.

                        Originally posted by 6hk71400 View Post
                        Correct me if I am wrong, but I always thought that timing effects dwell, but dwell does not affect timing. After reading this tread, I don't think that has been clearly stated. I always set the timing first, then set the dwell, but after a couple of strokes and a seizure, I may be wrong in my memory. The medications I take and rehab has brought me back to 90 percent but sometimes I don't trust my memory.


                        Bob Miles
                        Tucson AZ
                        Bob, sorry about the health issues. We never know when the next physical "ambush" will happen, but a risk we all face. Regarding timing...I think it is a subject we often conflate.(So,please, don't take this as a put-down condescending post. I'm as guilty, as anyone, of losing focus, and confusing the two)

                        In our engines, there are two cams involved in timing. While both are related, and one affects the other, there's "Valve" timing, and "ignition" timing. First, the valve timing, a purely mechanical function, has to be performed. Once the main engine cam by way of proper cam gear/crank gear, is properly set in place, it is further adjusted by "valve" adjustment, and those related components.

                        Once the "mechanical" components are set...comes "ignition timing." Here, we encounter the second cam, the distributor cam. As I posted earlier, this is where electrical meets mechanical. So, "Mechanical timing" & "Ignition timing." The distributor (ignition) cam, something that is usually so reliable, that it can lead to all sorts of trouble and confusion if ignored.

                        A good example, is my 1951 Land Cruiser. I acquired it in 1988. It had sat for years. In 1971, the car had less than 51,000 miles. In 1988, 56,000 miles. When I got it, there was a skip in the engine. New ignition points, rotor, condenser, spark plugs, distributor cap, and plug wires, and it still had the skip. Finally, off with the valve covers, and a mechanical valve adjustment....and the skip remained.



                        Like the previous owners, I parked the car, moved on to other things, and would occasionally, fire up the car, take a short drive, but totally disgusted with the mysterious skip. Then one day, while pilfering through a "bulk buy" I had made on a stash of Studebaker parts, I discovered a NOS distributor. Almost as an afterthought, I installed it in my Land Cruiser. To my surprise, it solved the skip. Apparently, the original distributor had a bad distributor cam lobe. I've often wondered, if that one overlooked problem, was what saved this car from being used up, worn out, and discarded. I suppose we'll never know.
                        John Clary
                        Greer, SC

                        SDC member since 1975

                        Comment


                        • #27
                          Thanks John. I am doing great really and not worried about what the next ambush may bring or if even I have another one. After surviving nightly mortar attacks plus the constant small arms fire when I was out of the base area while I was TDY in Saigon in 1973, I always try to take everything in stride.

                          Thanks for the refresher on timing. Having either a Studebaker six or eight in tune is a joy to hear and drive.

                          Bob Miles
                          Tucson AZ

                          Comment


                          • #28
                            Originally posted by 6hk71400 View Post
                            Thanks John. I am doing great really and not worried about what the next ambush may bring or if even I have another one. After surviving nightly mortar attacks plus the constant small arms fire when I was out of the base area while I was TDY in Saigon in 1973...
                            Bob Miles
                            Tucson AZ
                            Understand that Bob...I was there for the little dust-up known as "The Tet Offensive". We got it while "in base" area...the "mortars" lobbed at us, were actually 122mm rockets. A few weeks before I finished my tour...I was ordered to fill in the elaborate "fox hole" I had dug next to my barracks. I got so fed up with all the choking dust (and subsequent sore throat) stirred up when we had to scramble to our bunkers, that I spent several days, digging my personal hole in the ground. I scrounged up an old chair to sit in, and I even stored some spare C-ration kits, so I could have a snack while waiting for the "all-clear" signal. A few weeks before my time to leave, we had some of those monsoon gully washer rains that flooded my sanctuary.
                            I think they were afraid someone would inadvertently stumble in and drown. Filling that hole back in, while enduring the tropical heat, was much easier that digging it. Knowing that, by then, I was a "short timer" helped as well.
                            John Clary
                            Greer, SC

                            SDC member since 1975

                            Comment


                            • #29
                              Originally posted by 6hk71400 View Post
                              Correct me if I am wrong, but I always thought that timing effects dwell, but dwell does not affect timing. After reading this tread, I don't think that has been clearly stated. I always set the timing first, then set the dwell, but after a couple of strokes and a seizure, I may be wrong in my memory. The medications I take and rehab has brought me back to 90 percent but sometimes I don't trust my memory.

                              Bob Miles
                              Tucson AZ
                              =============

                              Hi Bob,

                              If I change the dwell very much with the distributor installed in the engine, the ignition timing will change too.
                              I think it's about 1 for 1, since the dwell angle is the total "time" the points are closed, so an extra degree of dwell adds 1/2 degree to each end of the points closed period.
                              BUT the spark happens on the end when the points open so is only affected by the 1/2 degree added there.
                              HOWEVER since the distributor turns at 1/2 engine rpm, 1 distributor degree = 2 crankshaft degrees, which is how ignition timing is referenced.

                              So, set the point gap, check the dwell, then finally check the ignition timing.

                              Oh, and then with the vac advance plugged on the carb,I rev the engine up looking for a smooth ignition timing increase/decrease as rpms change to be sure the centrifugal advance is actually working.
                              If it ain't, then I'm going to have to go back into the distributor to fix and clean, so the points dwell will have to be checked again.

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