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RE: [AirVW] reducing stroke to 50mm

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  • Bruno De Michelis
    If you will remain below or at 2000 r.p.m. the stroke can be fairly long, but you do not wish to reach a very vibrating result. ... From:
    Message 1 of 15 , Aug 3, 2013
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      Message
      If you will remain below or at 2000 r.p.m. the stroke can be fairly long, but you do not wish to reach  a very vibrating result.
      -----Original Message-----
      From: AirVW@yahoogroups.com [mailto:AirVW@yahoogroups.com] On Behalf Of Rogelio Serrano
      Sent: 04/ 08/ 2013 1:34 PM
      To: AirVW@yahoogroups.com
      Subject: Re: [AirVW] reducing stroke to 50mm




      On Sun, Aug 4, 2013 at 11:00 AM, Bruno De Michelis <msmprod@...> wrote:
       

      I think you will need a custom one and then, if your purpose is to increase
      the engine's r.p.m., you better re-calculate your piston's linear speed.
      Make sure that the custom crank assembly is well balanced.



      yes.

      im not going for crazy high rpms. its more for reducing the loads on the "bottom end". it will be used with a psru. prop will be run at less than 2000 rpm.

      maybe a longer rod will be needed. with a much lighter piston. im looking at forged racing motorcycle pistons.  

      thanks
       

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    • garywolf@rogers.com
      From a practical point of view, many VW 1200 engines spin to 7000 rpms regularly without ring or other component failure, and the 1600 s do 6200 rpms using
      Message 2 of 15 , Aug 4, 2013
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        From a practical point of view, many VW 1200 engines spin to 7000 rpms regularly without ring or other component failure, and the 1600's do 6200 rpms using only stock rotating and reciprocating parts that have been balanced. Formula Vee auto racing has shown this.

        Gary Wolf



        --- In AirVW@yahoogroups.com, "Bruno De Michelis" <msmprod@...> wrote:
        >
        > I think you will need a custom one and then, if your purpose is to increase
        > the engine's r.p.m., you better re-calculate your piston's linear speed.
        > Make sure that the custom crank assembly is well balanced.
        >
        > -----Original Message-----
        > From: AirVW@yahoogroups.com [mailto:AirVW@yahoogroups.com] On Behalf Of
        > Rogelio Serrano
        > Sent: 04/ 08/ 2013 12:35 PM
        > To: AirVW@yahoogroups.com
        > Subject: [AirVW] reducing stroke to 50mm
        >
        >
        > hi,
        >
        > im looking for a crank for a type 1 or type 4 engine with reduced stroke.
        > does such a thing exists? do i need a custom billet crank?
        >
        > a shorter conn rod would be needed also but thats for later.
        >
        > thanks
        >
        >
        > ------------------------------------
        >
        > Yahoo! Groups Links
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        >
        >
        >
        >
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        > No virus found in this message.
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        > Version: 2013.0.3392 / Virus Database: 3209/6549 - Release Date: 08/03/13
        >
      • Rogelio Serrano
        ... can they sustain that for several hours?
        Message 3 of 15 , Aug 4, 2013
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          On Sun, Aug 4, 2013 at 7:47 PM, <garywolf@...> wrote:
           



          From a practical point of view, many VW 1200 engines spin to 7000 rpms regularly without ring or other component failure, and the 1600's do 6200 rpms using only stock rotating and reciprocating parts that have been balanced. Formula Vee auto racing has shown this.

          Gary Wolf


          interesting ill check out formula vee auto racing then.

          can they sustain that for several hours? 
           


        • Rogelio Serrano
          ... I was led to believe that it can only be done for short periods. And its going to shorten the life of the engine to a few hours.
          Message 4 of 15 , Aug 4, 2013
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            On Sun, Aug 4, 2013 at 7:47 PM, <garywolf@...> wrote:
             



            From a practical point of view, many VW 1200 engines spin to 7000 rpms regularly without ring or other component failure, and the 1600's do 6200 rpms using only stock rotating and reciprocating parts that have been balanced. Formula Vee auto racing has shown this.

            Gary Wolf



            I was led to believe that it can only be done for short periods. And its going to shorten the life of the engine to a few hours.
             


          • mict04
            Hi Rogelio, First I am not an expert so these are just my thoughts, I hope some help. Second, I do not have a case or block in hand so my ideas are just
            Message 5 of 15 , Aug 4, 2013
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              Hi Rogelio,

              First I am not an expert so these are just my thoughts,
              I hope some help.
              Second, I do not have a case or block in hand so my ideas are just innitian thoughts from memory that might not work.


              If you are using stock or near stock case you will need longer rods when shortening crank stroke (the circle).
              You will also want to make sure head to piston TDC stays the same so you dont affect compression to much, (or is it compressed volume).

              This crank stroke reduction may present an opertunity if you have access to a lathe. As you may be able to cut down the base of cylinder by ammount reduced in stroke or there abouts. This would save some weight.

              I have heard of people cutting down crank shaft bearing surface were rods go in order to reduce stroke a little bit. But then you have the problem of finding bearings and rods to match, could be hard to find unless you make. You also end up with a weeker crank shaft but we are talking low power/low RPM.

              All this said; if it were my project I might be looking rather at going high stroke and small piston diameter. The stroke would give you the torque to turn big propeller without Reduction drive but the small piston diameter would keep the HP down to were you want it to be, and adjusting prop pitch to match. I don't know if there is a weight savings going to smaller cylinders and pistons other then the simplicity of the drive, but at least most parts are available off the shelf. But you would have to do the math to make sure volumes and compressions are ajusted to keep you out of high compression specialty gas.
              You would need to make on a lathe some donuts type of washer/shim/insert to site cylinders on base tight and on head tight so they are not loose and centered properly. But that is simple to make.
              If you use heads that cane with case bolts will fit with room to spare around cylinders. If instead of using shims/donuts you try to use heads from smaller cylinder engine to match cylinders you will run into headacks trying to match case bolts into head, might not work.
              The bigger heads are better anyway, more mass more cooling ability.

              Your case and crank would be so over strong you may have a very long lasting engine.

              Michel






              --- In AirVW@yahoogroups.com, Rogelio Serrano <rogelio.serrano@...> wrote:
              >
              > hi,
              >
              > im looking for a crank for a type 1 or type 4 engine with reduced
              > stroke. does such a thing exists? do i need a custom billet crank?
              >
              > a shorter conn rod would be needed also but thats for later.
              >
              > thanks
              >
            • Bruno De Michelis
              Correct! 7 to 8 hours, in most cases. ... From: AirVW@yahoogroups.com [mailto:AirVW@yahoogroups.com] On Behalf Of Rogelio Serrano Sent: 04/ 08/ 2013 10:05 PM
              Message 6 of 15 , Aug 4, 2013
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                Message
                Correct! 7 to 8 hours, in most cases.
                -----Original Message-----
                From: AirVW@yahoogroups.com [mailto:AirVW@yahoogroups.com] On Behalf Of Rogelio Serrano
                Sent: 04/ 08/ 2013 10:05 PM
                To: AirVW@yahoogroups.com
                Subject: Re: [AirVW] Re: reducing stroke to 50mm




                On Sun, Aug 4, 2013 at 7:47 PM, <garywolf@...> wrote:
                 



                From a practical point of view, many VW 1200 engines spin to 7000 rpms regularly without ring or other component failure, and the 1600's do 6200 rpms using only stock rotating and reciprocating parts that have been balanced. Formula Vee auto racing has shown this.

                Gary Wolf



                I was led to believe that it can only be done for short periods. And its going to shorten the life of the engine to a few hours.
                 


                No virus found in this message.
                Checked by AVG - www.avg.com
                Version: 2013.0.3392 / Virus Database: 3209/6549 - Release Date: 08/03/13

              • garywolf@rogers.com
                I am not saying that the entire engine can sustain this for hours at a time, but either the ring floats or it does not. Piston acceleration and ring mass
                Message 7 of 15 , Aug 4, 2013
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                  I am not saying that the entire engine can sustain this for hours at a time, but either the ring floats or it does not. Piston acceleration and ring mass determine whether this will occur. Again, read Jennings.

                  A VW direct drive will not likely be revved past 3600 rpms because it is prop limited. The available redrive is 1.6:1 and does not require the engine to rev higher than when in direct drive, the reason being that they want to turn a larger diameter prop.

                  I can easily state that at 6200 rpms the stock rings do not float because I have several seasons of this rpm on a 69mm stroke engine.

                  Gary Wolf




                  --- In AirVW@yahoogroups.com, Rogelio Serrano <rogelio.serrano@...> wrote:
                  >
                  > On Sun, Aug 4, 2013 at 7:47 PM, <garywolf@...> wrote:
                  >
                  > > **
                  > >
                  > >
                  > >
                  > >
                  > > From a practical point of view, many VW 1200 engines spin to 7000 rpms
                  > > regularly without ring or other component failure, and the 1600's do 6200
                  > > rpms using only stock rotating and reciprocating parts that have been
                  > > balanced. Formula Vee auto racing has shown this.
                  > >
                  > > Gary Wolf
                  > >
                  > > interesting ill check out formula vee auto racing then.
                  >
                  > can they sustain that for several hours?
                  >
                • Rogelio Serrano
                  ... im trying to optimize the engine power and efficiency within the limits imposed by the case. i dont want to exceed the design piston thrust at TDC becauses
                  Message 8 of 15 , Aug 5, 2013
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                    On Mon, Aug 5, 2013 at 12:00 AM, mict04 <andre04@...> wrote:
                     

                    Hi Rogelio,

                    First I am not an expert so these are just my thoughts,
                    I hope some help.
                    Second, I do not have a case or block in hand so my ideas are just innitian thoughts from memory that might not work.

                    If you are using stock or near stock case you will need longer rods when shortening crank stroke (the circle).
                    You will also want to make sure head to piston TDC stays the same so you dont affect compression to much, (or is it compressed volume).

                     
                    im trying to optimize the engine power and efficiency within the limits imposed by the case. i dont want to exceed the design piston thrust at TDC becauses it causes fatigue cracks in the case, maybe even exceeding the capacity of the bearings. the only way is to go higher rpm and there are well known ways to do that safely nowadays. the case is simply not strong enough to take the increased strain of increased displacement for a reasonable fatigue life.

                    i want to reduce the combustion chamber volume by half. this will cut the surface area for heat absorption. i also want to increase the fin area by the fat fin mod. this will allow me to use the miller cycle and drop the EGT down to diesel levels. diesel variable geometry turbos are common nowadays.

                    running on the miller cycle should improve fuel efficiency by 50% at least. that's already worthwhile in my opinion.

                    running WOT at 6000 rpm for 250 hours with even less strain than the stock engine is possible.
                     

                    This crank stroke reduction may present an opertunity if you have access to a lathe. As you may be able to cut down the base of cylinder by ammount reduced in stroke or there abouts. This would save some weight.


                    im going to use stock 126mm rods. going to 100mm rods will have benefits because i can cut down the barrels and the pushrods. there are many ways to reduce the stock rod weight. the rod big end will be reduced in width by 2mm on both sides. thin the web in the shank. and take off material from the top and stepping the width of the small end and bottom of the bottom end. the compression is more or less double the tension in the rod.

                    i going to use the cutaway piston design too. im targetting a weght of about 3/4 the original assembly.

                    I have heard of people cutting down crank shaft bearing surface were rods go in order to reduce stroke a little bit. But then you have the problem of finding bearings and rods to match, could be hard to find unless you make. You also end up with a weeker crank shaft but we are talking low power/low RPM.


                    i want to maintain the 55mm diameter in the rod journals. i want to narrow down the rod journal so i can use bigger fillet radii and thicker webs in the throws. the only way to go is custom crank and more advanced engine oil.
                     

                    All this said; if it were my project I might be looking rather at going high stroke and small piston diameter. The stroke would give you the torque to turn big propeller without Reduction drive but the small piston diameter would keep the HP down to were you want it to be, and adjusting prop pitch to match. I don't know if there is a weight savings going to smaller cylinders and pistons other then the simplicity of the drive, but at least most parts are available off the shelf. But you would have to do the math to make sure volumes and compressions are ajusted to keep you out of high compression specialty gas.
                    You would need to make on a lathe some donuts type of washer/shim/insert to site cylinders on base tight and on head tight so they are not loose and centered properly. But that is simple to make.
                    If you use heads that cane with case bolts will fit with room to spare around cylinders. If instead of using shims/donuts you try to use heads from smaller cylinder engine to match cylinders you will run into headacks trying to match case bolts into head, might not work.
                    The bigger heads are better anyway, more mass more cooling ability.

                    Your case and crank would be so over strong you may have a very long lasting engine.

                    Michel



                    --- In AirVW@yahoogroups.com, Rogelio Serrano <rogelio.serrano@...> wrote:
                    >
                    > hi,
                    >
                    > im looking for a crank for a type 1 or type 4 engine with reduced
                    > stroke. does such a thing exists? do i need a custom billet crank?
                    >
                    > a shorter conn rod would be needed also but thats for later.
                    >
                    > thanks
                    >


                  • Rogelio Serrano
                    On Mon, Aug 5, 2013 at 5:21 AM, Bruno De Michelis ... why is that? the bearings main failed? the case cracked? the rods broke?
                    Message 9 of 15 , Aug 5, 2013
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                      On Mon, Aug 5, 2013 at 5:21 AM, Bruno De Michelis
                      <msmprod@...> wrote:
                      >
                      >
                      >
                      > Correct! 7 to 8 hours, in most cases.

                      why is that? the bearings main failed? the case cracked? the rods broke?

                      > -----Original Message-----
                      > From: AirVW@yahoogroups.com [mailto:AirVW@yahoogroups.com] On Behalf Of Rogelio Serrano
                      > Sent: 04/ 08/ 2013 10:05 PM
                      > To: AirVW@yahoogroups.com
                      > Subject: Re: [AirVW] Re: reducing stroke to 50mm
                      >
                      >
                      >
                      >
                      > On Sun, Aug 4, 2013 at 7:47 PM, <garywolf@...> wrote:
                      >>
                      >>
                      >>
                      >>
                      >>
                      >> From a practical point of view, many VW 1200 engines spin to 7000 rpms regularly without ring or other component failure, and the 1600's do 6200 rpms using only stock rotating and reciprocating parts that have been balanced. Formula Vee auto racing has shown this.
                      >>
                      >> Gary Wolf
                      >>
                      >>
                      >
                      > I was led to believe that it can only be done for short periods. And its going to shorten the life of the engine to a few hours.
                      >
                      >>
                      >>
                      >
                      > No virus found in this message.
                      > Checked by AVG - www.avg.com
                      > Version: 2013.0.3392 / Virus Database: 3209/6549 - Release Date: 08/03/13
                      >
                      >
                    • Bruno De Michelis
                      Internal combustion engines overheat when overworking. That is the main cause of various mechanical failures and that is also why most engines are today liquid
                      Message 10 of 15 , Aug 6, 2013
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                        Internal combustion engines overheat when overworking. That is the main
                        cause of various mechanical failures and that is also why most engines are
                        today liquid cooled, maintaining more easily a constant temperature.
                        Air cooling can be effective to a certain extent because the boundary layer
                        can act 'till a certain speed, or viceversa can act against the optimal
                        engine running temperature if the finning is excessive.
                        I can clearly remember an instance, in the '70s, in which the engine of a
                        500cc GP Kawasaki seazed at the end of the straight, on Monza circuit,
                        because the area of the cooling fins was excessive and the cyliders
                        literally schrunk.

                        -----Original Message-----
                        From: AirVW@yahoogroups.com [mailto:AirVW@yahoogroups.com] On Behalf Of
                        Rogelio Serrano
                        Sent: 06/ 08/ 2013 3:24 PM
                        To: AirVW@yahoogroups.com
                        Subject: Re: [AirVW] Re: reducing stroke to 50mm


                        On Mon, Aug 5, 2013 at 5:21 AM, Bruno De Michelis <msmprod@...>
                        wrote:
                        >
                        >
                        >
                        > Correct! 7 to 8 hours, in most cases.

                        why is that? the bearings main failed? the case cracked? the rods broke?

                        > -----Original Message-----
                        > From: AirVW@yahoogroups.com [mailto:AirVW@yahoogroups.com] On Behalf
                        > Of Rogelio Serrano
                        > Sent: 04/ 08/ 2013 10:05 PM
                        > To: AirVW@yahoogroups.com
                        > Subject: Re: [AirVW] Re: reducing stroke to 50mm
                        >
                        >
                        >
                        >
                        > On Sun, Aug 4, 2013 at 7:47 PM, <garywolf@...> wrote:
                        >>
                        >>
                        >>
                        >>
                        >>
                        >> From a practical point of view, many VW 1200 engines spin to 7000
                        >> rpms regularly without ring or other component failure, and the
                        >> 1600's do 6200 rpms using only stock rotating and reciprocating parts
                        >> that have been balanced. Formula Vee auto racing has shown this.
                        >>
                        >> Gary Wolf
                        >>
                        >>
                        >
                        > I was led to believe that it can only be done for short periods. And
                        > its going to shorten the life of the engine to a few hours.
                        >
                        >>
                        >>
                        >
                        > No virus found in this message.
                        > Checked by AVG - www.avg.com
                        > Version: 2013.0.3392 / Virus Database: 3209/6549 - Release Date:
                        > 08/03/13
                        >
                        >


                        ------------------------------------

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                      • racerjerry2
                        ... A `perfect racing crankshaft would theoretically be balanced at EACH JOURNAL. Production crankshafts are statically and dynamically balanced by
                        Message 11 of 15 , Aug 6, 2013
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                          --- In AirVW@yahoogroups.com, Rogelio Serrano <rogelio.serrano@...> wrote:
                          >
                          > On Mon, Aug 5, 2013 at 5:21 AM, Bruno De Michelis
                          > <msmprod@...> wrote:
                          > >
                          > >
                          > >
                          > > Correct! 7 to 8 hours, in most cases.
                          >
                          > why is that? the bearings main failed? the case cracked? the rods broke?

                          A `perfect' racing crankshaft would theoretically be balanced at EACH JOURNAL. Production crankshafts are statically and dynamically balanced by adding/subtracting weight at each end, but because of economic and manufacturing difficulty, they usually have no center counterweights. Because of this, at high RPM's, the crankshaft tends to bow in the middle. Presuming you have a good oiling system, main bearing problems generally appear at the center main. The bending forces increase to the square of RPM's, so at the lower operational speeds of aircraft engines (limited by propeller efficiency), problems such as this are rarely encountered.
                        • Rogelio Serrano
                          ... counterweights? what causes them to fail? besides cooling? not enough oil to the heads i guess. how powerful and reliable are engines with counterwieghts
                          Message 12 of 15 , Aug 6, 2013
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                            On Tue, Aug 6, 2013 at 8:21 PM, racerjerry2 <gki@...> wrote:
                             



                            --- In AirVW@yahoogroups.com, Rogelio Serrano <rogelio.serrano@...> wrote:
                            >
                            > On Mon, Aug 5, 2013 at 5:21 AM, Bruno De Michelis
                            > <msmprod@...> wrote:
                            > >
                            > >
                            > >
                            > > Correct! 7 to 8 hours, in most cases.
                            >
                            > why is that? the bearings main failed? the case cracked? the rods broke?

                            A `perfect' racing crankshaft would theoretically be balanced at EACH JOURNAL. Production crankshafts are statically and dynamically balanced by adding/subtracting weight at each end, but because of economic and manufacturing difficulty, they usually have no center counterweights. Because of this, at high RPM's, the crankshaft tends to bow in the middle. Presuming you have a good oiling system, main bearing problems generally appear at the center main. The bending forces increase to the square of RPM's, so at the lower operational speeds of aircraft engines (limited by propeller efficiency), problems such as this are rarely encountered.

                            thats true for non counterweighted cranks. how about the those with counterweights? what causes them to fail? besides cooling? not enough oil to the heads i guess.

                            how powerful and reliable are engines with counterwieghts and hvx mods?

                            most probably heat related. dropped valve seats. revmaster pioneered the high temp valve seats. and we have the fat fin mods.

                            anybody tried all those together yet?
                             

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