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Re: Technical question about heat side fairings vis inside engine covers...

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  • The Model Citizen
    Hi Gavin From experience (several non faired dukes and a DB1) it makes no difference to the belt performance. The thing to remember is that the belts are
    Message 1 of 17 , Nov 1, 2011
      Hi Gavin

      From experience (several non faired dukes and a DB1) it makes no difference to the belt performance. The thing to remember is that the belts are uncovered/ventilated they can allow in dirt and water which will affect belt and pulley life.
      Modern belts are of much better construction now as well, that's if you can still get the tooth profile.

      The only problem I had with a belt is when a tensioner roller bearing seized. This DID overheat the belt and it failed after 1000 km. Mid corner at about 175kmh! I still remember the "tink" sound when the valves touched the piston. Luckily for me the valves closed, it didn't lock up and I just limped away on one.

      Richard



      On 01/11/2011 03:46, Gavin Bedggood wrote:
       

      On a fully faired air cooled bike like a Bimota DB1 (750 Ducati Pantah with full flow oil cooler) is it better for belt life and "general engine cooling" to put some air holes on the belt covers to get some air flow through them???  Or would it just let in even hotter air from inside the fairing coming off the header pipes etc???
       
      Opinions anyone?
       
      Regards
      Gavin



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    • Rick Hammond
      Gavin, Richard, I know lots of auto belts live quite sealed up.. I suppose there could be an effect over time though. That said, Ducati has been ducting on
      Message 2 of 17 , Nov 1, 2011
        Gavin, Richard,
        I know lots of auto belts live quite sealed up..  I suppose there could be an effect over time though.
        That said, Ducati has been ducting on the Streetfighter and 1198 motors;
        http://jemblankz-info.blogspot.com/2011/07/ducati-2009.html   (scroll down)
        The other thing; look at the idlers.  Larger diameter?  Makes sense to me.

        Ok, we measure tension by 'twang' (frequency) these days.. wonder how the tension changes when hot?
        Cheers,
        Rick

        On 01/11/2011 04:52, The Model Citizen wrote:
         

        Hi Gavin

        From experience (several non faired dukes and a DB1) it makes no difference to the belt performance. The thing to remember is that the belts are uncovered/ventilated they can allow in dirt and water which will affect belt and pulley life.
        Modern belts are of much better construction now as well, that's if you can still get the tooth profile.

        The only problem I had with a belt is when a tensioner roller bearing seized. This DID overheat the belt and it failed after 1000 km. Mid corner at about 175kmh! I still remember the "tink" sound when the valves touched the piston. Luckily for me the valves closed, it didn't lock up and I just limped away on one.

        Richard



        On 01/11/2011 03:46, Gavin Bedggood wrote:

         

        On a fully faired air cooled bike like a Bimota DB1 (750 Ducati Pantah with full flow oil cooler) is it better for belt life and "general engine cooling" to put some air holes on the belt covers to get some air flow through them???  Or would it just let in even hotter air from inside the fairing coming off the header pipes etc???
         
        Opinions anyone?
         
        Regards
        Gavin



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        Checked by AVG - www.avg.com
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    • Ian
      ... Tooth belts tighten significantly when they get hot, both the rubber and the fibre in the belt have negative co-eff of expansion. Cheers IAN
      Message 3 of 17 , Nov 1, 2011
        >Ok, we measure tension by 'twang' (frequency) these days.. wonder
        >how the tension changes when hot?


        Tooth belts tighten significantly when they get hot, both the rubber
        and the fibre in the belt have negative co-eff of expansion.


        Cheers IAN


        See www.drysdalev8.com for :
        - Drysdale 750-V8 Sports & 1000-V8 Cruiser
        - DRYVTECH 2x2x2 Experimental
        - Carberry Enfield 1000cc V-Twin
        - Drysdale Hillclimb Open Wheeler
      • Rick Hammond
        Interesting to know.. how significant would the expansion of the aluminum cylinder / head be? I suppose if you wanted real ventilation you have spinning
        Message 4 of 17 , Nov 1, 2011
          Interesting to know..  how significant would the expansion of the aluminum cylinder / head be?
          I suppose if you wanted real ventilation you have spinning pulleys; you could have wee fans extracting hot air.. (filter intakes)
          Cheers,
          Rick

          On 01/11/2011 11:02, Ian wrote:  


          >Ok, we measure tension by 'twang' (frequency) these days.. wonder
          >how the tension changes when hot?

          Tooth belts tighten significantly when they get hot, both the rubber
          and the fibre in the belt have negative co-eff of expansion.

          Cheers IAN

          See www.drysdalev8.com for :
          - Drysdale 750-V8 Sports & 1000-V8 Cruiser
          - DRYVTECH 2x2x2 Experimental
          - Carberry Enfield 1000cc V-Twin
          - Drysdale Hillclimb Open Wheeler


        • Ian
          ... SNIP ... Growth due to temperature is significant, taking crank to cam CD as say 350mm and say 75 deg C temp change (cold morning), that gives a growth of
          Message 5 of 17 , Nov 1, 2011
            >Interesting to know.. how significant would the expansion of the
            >aluminum cylinder / head be?

            SNIP

            >>Tooth belts tighten significantly when they get hot, both the rubber
            >>and the fibre in the belt have negative co-eff of expansion.


            Growth due to temperature is significant, taking crank to cam
            CD as say 350mm and say 75 deg C temp change (cold morning),
            that gives a growth of 0.31 mm. ( Exp of aluminium 1.2 x 10E-5 )
            OK, we may not get an even 75 deg C across the crankcases,
            cyl & head - but 0.30 mm won't be far out.

            The belt won't be far off that temperature either, and their ( -ve )
            expansion is higher than that. Just a wild guess, but my
            experience with increase in belt tension on my Rotax KTM would
            be an "effective contraction" of 1.0mm ( in CD ) or maybe even a
            bit more ? ( No ventilation on that belt BTW )

            Rich, you're got more experience with rubber bands than me,
            would 1.0mm "effective contraction" be close ?


            Cheers IAN


            See www.drysdalev8.com for :
            - Drysdale 750-V8 Sports & 1000-V8 Cruiser
            - DRYVTECH 2x2x2 Experimental
            - Carberry Enfield 1000cc V-Twin
            - Drysdale Hillclimb Open Wheeler
          • Arthur Middleton
            ... What is your source on negative coefficients of expansion for rubber? Or am I misinterpreting the post? Arthur.
            Message 6 of 17 , Nov 1, 2011
              On 01/11/2011 15:45, Ian wrote:
              > The belt won't be far off that temperature either, and their ( -ve )
              > expansion is higher than that. Just a wild guess, but my experience
              > with increase in belt tension on my Rotax KTM would be an "effective
              > contraction" of 1.0mm ( in CD ) or maybe even a bit more ? ( No
              > ventilation on that belt BTW ) Rich, you're got more experience with
              > rubber bands than me, would 1.0mm "effective contraction" be close ?

              What is your source on negative coefficients of expansion for rubber? Or
              am I misinterpreting the post?

              Arthur.
            • Ian
              ... An excellent week long course I did on seals when I was working in hydraulics, many moons ago, many ( most ? ) polymers exhibit this characteristic. It
              Message 7 of 17 , Nov 1, 2011
                >What is your source on negative coefficients of expansion for rubber?


                An excellent week long course I did on seals when I was working in
                hydraulics, many moons ago, many ( most ? ) polymers exhibit this
                characteristic. It was put on by Ludowici, a most unlikely name for
                an old Australian seal manufacturer, but an excellent company.

                I can't point you to any particular source on the net, but I can recall
                reading the same thing when researching tooth belts from time to
                time.

                Of course I should be more specific when I say "rubber", like many
                people, I do get a it lazy with terminology, with "rubber" being used
                for "rubber like" products, not just natural "tree rubber". Nitrile and
                Urethane are the 2 main "synthetic rubbers", but there are numerous
                other polymers that are also called "rubber".



                Cheers IAN


                See www.drysdalev8.com for :
                - Drysdale 750-V8 Sports & 1000-V8 Cruiser
                - DRYVTECH 2x2x2 Experimental
                - Carberry Enfield 1000cc V-Twin
                - Drysdale Hillclimb Open Wheeler
              • Otto Nikolaus
                ... Wouldn t Neoprene be the best known synthetic rubber, and how about latex for the natural stuff (or does that have some dodgy meaning Down Under)? Otto
                Message 8 of 17 , Nov 1, 2011
                  On 1 November 2011 22:41, Ian <iwd@...> wrote:

                  An excellent week long course I did on seals when I was working in
                  hydraulics, many moons ago, many ( most ? ) polymers exhibit this
                  characteristic.  It was put on by Ludowici, a most unlikely name for
                  an old Australian seal manufacturer, but an excellent company.

                  I can't point you to any particular source on the net, but I can recall
                  reading the same thing when researching tooth belts from time to
                  time.

                  Of course I should be more specific when I say "rubber", like many
                  people, I do get a it lazy with terminology, with "rubber" being used
                  for "rubber like" products, not just natural "tree rubber".   Nitrile and
                  Urethane are the 2 main "synthetic rubbers", but there are numerous
                  other polymers that are also called "rubber".

                  Wouldn't Neoprene be the best known synthetic rubber, and how about 'latex' for the natural stuff (or does that have some dodgy meaning Down Under)?

                  Otto

                • Arthur Middleton
                  ... I think you may have picked that up wrong. I m pretty sure that polymers have positive expansion coefficients. Generally much greater than aluminium, for
                  Message 9 of 17 , Nov 2, 2011
                    On 01/11/2011 22:41, Ian wrote:
                    >> What is your source on negative coefficients of expansion for rubber?
                    >
                    > An excellent week long course I did on seals when I was working in
                    > hydraulics, many moons ago, many ( most ? ) polymers exhibit this
                    > characteristic. It was put on by Ludowici, a most unlikely name for
                    > an old Australian seal manufacturer, but an excellent company.
                    >
                    > I can't point you to any particular source on the net, but I can recall
                    > reading the same thing when researching tooth belts from time to
                    > time.
                    I think you may have picked that up wrong. I'm pretty sure that polymers
                    have positive expansion coefficients. Generally much greater than
                    aluminium, for example.

                    >
                    > Of course I should be more specific when I say "rubber", like many
                    > people, I do get a it lazy with terminology, with "rubber" being used
                    > for "rubber like" products, not just natural "tree rubber". Nitrile and
                    > Urethane are the 2 main "synthetic rubbers", but there are numerous
                    > other polymers that are also called "rubber".

                    I worked for some time in the rubber industry and the generic term
                    "rubber" is applied to many thermoset viscoelastic polymers, not just to
                    latex based rubbers.

                    Arthur.
                  • Ian
                    ... Interesting Arthur, can you shed any light on this negative co-eff of expansion issue ? Cheers IAN See www.drysdalev8.com for : - Drysdale 750-V8
                    Message 10 of 17 , Nov 2, 2011
                      >I worked for some time in the rubber industry and the generic term
                      >"rubber" is applied to many thermoset viscoelastic polymers, not just to
                      >latex based rubbers.


                      Interesting Arthur, can you shed any light on this negative
                      co-eff of expansion issue ?


                      Cheers IAN


                      See www.drysdalev8.com for :
                      - Drysdale 750-V8 Sports & 1000-V8 Cruiser
                      - DRYVTECH 2x2x2 Experimental
                      - Carberry Enfield 1000cc V-Twin
                      - Drysdale Hillclimb Open Wheeler
                    • Arthur Middleton
                      ... Not really. I was surprised when I read what you wrote, which is why I asked. I ve just now Googled it and didn t find any references to negative
                      Message 11 of 17 , Nov 2, 2011
                        On 02/11/2011 08:57, Ian wrote:
                        >> I worked for some time in the rubber industry and the generic term
                        >> "rubber" is applied to many thermoset viscoelastic polymers, not just to
                        >> latex based rubbers.
                        >
                        > Interesting Arthur, can you shed any light on this negative
                        > co-eff of expansion issue ?

                        Not really. I was surprised when I read what you wrote, which is why I
                        asked. I've just now Googled it and didn't find any references to
                        negative coefficients of expansion apart from some odd examples (water
                        between 0C and 4C, for example). I'm not a polymer expert so could have
                        been mistaken.

                        Re the rubber definition, we could simply use synthetic and natural to
                        distinguish between them. Many rubber compounds available use both.

                        Arthur.
                      • Ian
                        ... OK, I d better spend some time chasing up references to this, it s something that I thought was common knowledge. Cheers IAN See
                        Message 12 of 17 , Nov 2, 2011
                          > > Interesting Arthur, can you shed any light on this negative
                          > > co-eff of expansion issue ?
                          >
                          >Not really. I was surprised when I read what you wrote, which is why I
                          >asked. I've just now Googled it and didn't find any references to
                          >negative coefficients of expansion apart from some odd examples (water
                          >between 0C and 4C, for example). I'm not a polymer expert so could have
                          >been mistaken.


                          OK, I'd better spend some time chasing up references to this, it's
                          something that I thought was common knowledge.



                          Cheers IAN


                          See www.drysdalev8.com for :
                          - Drysdale 750-V8 Sports & 1000-V8 Cruiser
                          - DRYVTECH 2x2x2 Experimental
                          - Carberry Enfield 1000cc V-Twin
                          - Drysdale Hillclimb Open Wheeler
                        • Ian
                          ... For rubber bands that shrink with heat: http://scifun.chem.wisc.edu/homeexpts/rubberband.html http://www.physlink.com/education/askexperts/ae478.cfm
                          Message 13 of 17 , Nov 3, 2011
                            >OK, I'd better spend some time chasing up references to this, it's
                            >something that I thought was common knowledge.

                            For rubber bands that shrink with heat:

                            http://scifun.chem.wisc.edu/homeexpts/rubberband.html

                            http://www.physlink.com/education/askexperts/ae478.cfm

                            _____________________________________________________

                            For steel cord timing belts:

                            http://mulco.gwj.de/en/p_23170.htm

                            8. Ambient temperature, elongation under heat
                            The linear elongation under heat of the BRECO TIMING BELT with steel
                            cord tension members shows the same values as the linear elongation
                            under heat of a surrounding steel structure. No change of the
                            pre-tension force is then to be expected. In the case of a
                            surrounding aluminium structure and a rise of the ambient
                            temperature, a slight increase of the pre-tension can be expected.
                            The attendant linear path changes with the linear elongation
                            behaviour under heat of the surrounding structure.
                            Measures: The influence of elongation under heat in the belt and also
                            in the surrounding structure are minor. Temperature influences only
                            need to be taken into account in exceptional cases.
                            .................................................................................................

                            This states that aluminium blocks expand more than its timing belts,
                            steel about the same, but this is for a steel cord belt, so that's to be
                            expected.
                            _________________________________________________________

                            High performance tooth belts use Kelvar fibres for their tension
                            characteristics, these sites have tech details on Kevlar giving a small
                            negative co-eff of expansion, Carbon fibre too ( weird ?? ).

                            http://www2.dupont.com/Kevlar/en_US/assets/downloads/KEVLAR_Technical_Guide.pdf

                            http://www.stormcable.com/uploads/Thermal_expansion_data_table_tb06.pdf
                            ____________________________________________________________

                            This site gives thermal expansion of "Nitrile" as 5 times that of aluminium.
                            ( i.e - positive ) I was always under the impression that it was -ve ??

                            http://www.allsealsinc.com/oilsseals.html

                            Urethane is similar:

                            http://www.gallaghercorp.com/urethane/designguide/physicalconstants.shtml
                            ____________________________________________________________

                            So a typical tooth belt is close to neutral or has a slight contraction with
                            rising temperature, most of the increase in tension comes from the expansion
                            of the metal in the engine.

                            So it does get tighter, just that I thought more of the tension came from the
                            belt..........



                            Cheers IAN


                            See www.drysdalev8.com for :
                            - Drysdale 750-V8 Sports & 1000-V8 Cruiser
                            - DRYVTECH 2x2x2 Experimental
                            - Carberry Enfield 1000cc V-Twin
                            - Drysdale Hillclimb Open Wheeler
                          • Arthur Middleton
                            ... This is quite interesting. The rubber examples above are for longitudinal contraction in the direction of tension. The volumetric expansion coefficient may
                            Message 14 of 17 , Nov 3, 2011
                              On 03/11/2011 07:41, Ian wrote:
                              >> OK, I'd better spend some time chasing up references to this, it's
                              >> something that I thought was common knowledge.
                              > For rubber bands that shrink with heat:
                              >
                              > http://scifun.chem.wisc.edu/homeexpts/rubberband.html
                              >
                              > http://www.physlink.com/education/askexperts/ae478.cfm
                              >
                              > _____________________________________________________
                              >
                              > For steel cord timing belts:
                              >
                              > http://mulco.gwj.de/en/p_23170.htm
                              >
                              > 8. Ambient temperature, elongation under heat
                              > The linear elongation under heat of the BRECO TIMING BELT with steel
                              > cord tension members shows the same values as the linear elongation
                              > under heat of a surrounding steel structure. No change of the
                              > pre-tension force is then to be expected. In the case of a
                              > surrounding aluminium structure and a rise of the ambient
                              > temperature, a slight increase of the pre-tension can be expected.
                              > The attendant linear path changes with the linear elongation
                              > behaviour under heat of the surrounding structure.
                              > Measures: The influence of elongation under heat in the belt and also
                              > in the surrounding structure are minor. Temperature influences only
                              > need to be taken into account in exceptional cases.
                              > .................................................................................................
                              >
                              > This states that aluminium blocks expand more than its timing belts,
                              > steel about the same, but this is for a steel cord belt, so that's to be
                              > expected.
                              > _________________________________________________________
                              >
                              > High performance tooth belts use Kelvar fibres for their tension
                              > characteristics, these sites have tech details on Kevlar giving a small
                              > negative co-eff of expansion, Carbon fibre too ( weird ?? ).
                              >
                              > http://www2.dupont.com/Kevlar/en_US/assets/downloads/KEVLAR_Technical_Guide.pdf
                              >
                              > http://www.stormcable.com/uploads/Thermal_expansion_data_table_tb06.pdf
                              > ____________________________________________________________
                              >
                              > This site gives thermal expansion of "Nitrile" as 5 times that of aluminium.
                              > ( i.e - positive ) I was always under the impression that it was -ve ??
                              >
                              > http://www.allsealsinc.com/oilsseals.html
                              >
                              > Urethane is similar:
                              >
                              > http://www.gallaghercorp.com/urethane/designguide/physicalconstants.shtml
                              > ____________________________________________________________
                              >
                              > So a typical tooth belt is close to neutral or has a slight contraction with
                              > rising temperature, most of the increase in tension comes from the expansion
                              > of the metal in the engine.
                              >
                              > So it does get tighter, just that I thought more of the tension came from the
                              > belt..........

                              This is quite interesting. The rubber examples above are for
                              longitudinal contraction in the direction of tension. The volumetric
                              expansion coefficient may still be positive (I don't know), as with
                              Kevlar and carbon fibre. The next question is: what happens to rubber in
                              compression when it's heated?

                              Arthur.
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