Announcement

Collapse
No announcement yet.

Another timing belt question - noise and pulley overhang?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Another timing belt question - noise and pulley overhang?

    Been wondering about this for a while, the other timing belt thread has prompted me to post the question.

    I'm planning a final drive/reduction for my own boat using MXP 14mm pitch x 85mm wide belt, with provisionally 32 & 56 groove pulleys. Large (propellor) pulley running at about 450 rpm max., max power about 60 bhp.

    Two questions -
    First, anyone know how much noise to expect? I know noise tends to be subjective and don't expect anyone to be able to quote figures, but are they reasonably quiet at high powers?

    Second, how do I establish whether the pulleys will need supporting bearings on both sides, or can be open ended? I can design the layout so the pulleys are both as close to the bearings as physically practical.
    The prop shaft is 3" dia., I'm thinking in terms of 1.75" or 2" for the intermediate shaft.

    Thanks for any help

    Tim

  • #2
    Maximum torque times pulley diameter will determine the bending load on the shafts if only supported one side. As for the belt you should know that the hp capacity of any particular belt depends on the size of the pulleys it runs on and the rpm it runs at. The smaller the pulley at either end the lower the maximum power. The lower the rpm the lower the maximum torque. In either case the teeth on the belt are the limiting factor as they will be torn off if the maximum load is exceeded for a given number of engaged teeth.

    Cog belts are pretty quiet, especially at low rpms.
    Free software for calculating bolt circles and similar: Click Here

    Comment


    • #3
      As far as noise - if its a concern start out with a round tooth belt and pulley system - Iv seen the transition (from square/intermediate/round) in the automobile industry and they are much more forgiving,
      I had to get tension spot on with the square or else, also - leave some grow room for expansion - ALL OHC engines I work on are aluminum head -- some are aluminum block also - what this means is there will be an extreme growth rate between all the pulley systems and a belt that is silent running upon start up can be very noisy at normal operating temp. Just using this as an example as I dont know what kind of layout your drivetrain will be.

      Most of the OHC/DOHC engines I work on now are Hydraulically tensioned on the No-Load side of the belt, due to the nature of what your using it for this could prove to be a no-no due to coast down of the boat out-accelerating the prop, tension is then lost and the belt will self destruct - however - you could install a limiter - the hydraulics then take care of the "details" of normal operation and the limiter provides the failsafe...

      Comment


      • #4
        Originally posted by Evan
        Maximum torque times pulley diameter will determine the bending load on the shafts if only supported one side. As for the belt you should know that the hp capacity of any particular belt depends on the size of the pulleys it runs on and the rpm it runs at. The smaller the pulley at either end the lower the maximum power. The lower the rpm the lower the maximum torque. In either case the teeth on the belt are the limiting factor as they will be torn off if the maximum load is exceeded for a given number of engaged teeth.

        Cog belts are pretty quiet, especially at low rpms.

        I've used the maker's design manual to establish pulley sizes etc., including various 'duty factors', so that side of things ought to be OK

        Tim

        Comment


        • #5
          Originally posted by A.K. Boomer
          As far as noise - if its a concern start out with a round tooth belt and pulley system - Iv seen the transition (from square/intermediate/round) in the automobile industry and they are much more forgiving,
          I had to get tension spot on with the square or else, also - leave some grow room for expansion - ALL OHC engines I work on are aluminum head -- some are aluminum block also - what this means is there will be an extreme growth rate between all the pulley systems and a belt that is silent running upon start up can be very noisy at normal operating temp. Just using this as an example as I dont know what kind of layout your drivetrain will be.

          Most of the OHC/DOHC engines I work on now are Hydraulically tensioned on the No-Load side of the belt, due to the nature of what your using it for this could prove to be a no-no due to coast down of the boat out-accelerating the prop, tension is then lost and the belt will self destruct - however - you could install a limiter - the hydraulics then take care of the "details" of normal operation and the limiter provides the failsafe...
          This will be well away from any heat source, other than the belt itself and the bearings. I'm planning to incorporate provision for a small amount of tension adjustment by moving the smaller pulley and its shaft.

          Tim

          Comment

          Working...
          X