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1" Bore x 1" Stroke Vertical i.c. Engine

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  • My theory about this debacle is this---If, in setting up to cut a 50 tooth gear I went one hole too far each time, then the spaces between the teeth will be a very small amount larger each time I cut a space. This means that there will eventually be less room on the gears pitch diameter for teeth than was intended---but it's damned odd that it worked out so evenly to 48 teeth, and that it still meshed with the 25 tooth gear.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • your center to center distance must be an error, presumably.
      Was there not a recent thread about differing gear counts (pitch?) on the same C to C distance?
      Can an error be transcribed from that thread?
      just thinking out loud here,,,

      Comment


      • When using the plates on your rotary table or dividing head you count spaces not holes. I’ve made the same mistake. I’m amused that the gears meshed properly even though they didn’t have the right number of teeth. Funny how things work out sometimes.

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        • A small error would slightly change the width of the tooth, but since neither the depth of the tooth nor the blank diameter were changed, it is no surprise that the C-C distance was still OK.
          2801 3147 6749 8779 4900 4900 4900

          Keep eye on ball.
          Hashim Khan


          It's just a box of rain, I don't know who put it there.

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          • After much head scratching and reading the responses on three different forums, I come up with this. The math appears to be correct. On the first gear I cut which ended up with 48 teeth and not the 50 I was aiming for, I was going one space too many before each cut.
            What I have shown here is what the correct set-up should have been to get 50 teeth.
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

            Comment


            • I have to ask, how come this problem has not appeared before with one of the many other engines you built? I am pretty sure you customarily make your own gears each time. I am less confident but think that the 25/50 ratio is one you have used in the past as well. Bottom line, why have you not ran into the problem with other valve gear trains you made in the past?

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              • This is interesting. I would like learn the final answer.
                I have to ask, if the C-C distance is correct, and the blank dia is correct, and the 25T mesh properly, then where did the extra 2-tooth space go?

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                • I’m still thinking on this by my calculations when you got to the last tooth, the error would have been big enough to be easily seen. On a 48 tooth gear, the tooth spacing should be 7.5 deg. One turn and 17/20 holes is 7.4 deg. So 0.1 deg off times 48 puts your last cut off by 4.8 deg, more than half a tooth spacing off. Based on the work I’ve seen you do, I’m sure you would have caught that size of error.

                  When you cut the gear did you cut full depth in a single pass, or did you make multiple rotations around the gear blank until you got to full depth? Multiple rotations might smooth out the error.

                  Any chance you used the wrong set of holes in your dividing plate? One turn and 16/18 holes would give you 7.56 deg spacing (only a 0.05 deg off from the correct spacing for a 48 tooth gear).

                  When I get Time... I'll...

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                  • As far as I know, I made this gear using exactly the same math inputs as all my other gears. I didn't end up with any half teeth or unusually thick teeth. That's why it is such a puzzler. I have made many, many gears and never had a problem. I made this exact same gear for the Rockerblock engine and it has the correct number of teeth. If I made any mistakes with this gear it was probably from using one space to many on the divider plates. I'm going to make it again this afternoon using the information in the drawing I posted. I will let you know how that turns out.---Very, very weird!!!
                    Brian Rupnow
                    Design engineer
                    Barrie, Ontario, Canada

                    Comment


                    • Okay--Here we go, second time around!!--And this time it has 50 teeth, and it meshes fine with the 25 tooth gear on the engine, at the correct centers for a 25 tooth and a 50 tooth gear. Why did the other (first) 50 tooth gear end up with 48 teeth?---I have absolutely no idea. The blank size was the same, the material was the same. I must have set the sector arms at one hole more than they should have been set at on the 20 hole divider plate. That is the very first gear that I've made that didn't come out right---I've cut about 40 gears prior to the bad one. We'll remember that gear forever now, and double check my machine settings before I make any more gears.
                      Brian Rupnow
                      Design engineer
                      Barrie, Ontario, Canada

                      Comment


                      • Well, I am not a gear expert at all, but, may I assume that IF, for example, you had about .003 thou error on each tooth, you wouldn't see it by naked eye.
                        multiply .003 thou times 48teeth and the error is .144 thou. or perhaps 2 teeth.
                        The error got gradually consumed on each tooth a couple thou at a time, so you never saw it, no ?

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                        • Ringo--It's not so odd that I make an error once in a while. What is really odd is that the gear still meshed properly with it's 25 tooth mate. I would have expected at least one unusually wide space between teeth, or to be left with half a tooth after finishing the gear cutting. When cutting teeth on a gear (actually you cut the spaces between the teeth) the spaces are cut one at a time and the blank is indexed into position for the next cut. If you screw up, then when you index into the last position plus one, if the gear is good then you shouldn't be cutting any metal. If you somehow lose count of what you are doing, then you will be cutting metal, and that is a clear signal that you messed up. In this particular case, that didn't happen, so I seen nothing wrong with the gear.
                          Brian Rupnow
                          Design engineer
                          Barrie, Ontario, Canada

                          Comment


                          • Just a note on cutting gears. To avoid rounding errors its always better to leave the ratio as a fraction. In your case 90 tooth on the dividing head, cutting 50 tooth gear so 90/50= 1-40/50 or 1-4/5. so you need to turn 1-4/5 turns of your handle per tooth. You can use any hole circle divisible by 5. For example 1 full turn plus 16 spaces on a 20 circle or 20 on a 25 or 28 on a 35 etc.

                            I'm glad you were able to get it figured out. Looking forward to first run video.

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                            • Engine is reassembled and almost ready to go. Today I took a bit of time and made an adapter with 1/4"-32 threads on the end, which will screw into the sparkplug hole. It is hollow, and has an airline attached to it. I will screw it into the sparkplug hole tomorrow and hook a regulator onto it and apply some air pressure. This will let me see if I have any leaks in the intake or exhaust valve or around the ring.
                              Brian Rupnow
                              Design engineer
                              Barrie, Ontario, Canada

                              Comment


                              • That air adapter, if you made up a check valve and gauge to go with it would double up as a compression tester. Wouldn't it be nice to have the ability to get real compression readings for verification and troubleshooting?

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