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Rotocap in Exhaust Valve

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  • Rotocap in Exhaust Valve

    How the rotocap in exhaust valve works?

  • #2
    There is a collet or cotter which is on the valve cover fitted around the exhaust valve. The valve cover has number of inclined tracks machined into it. Each contains a ball and a spring. The balls runs on the race. Now when the valve is closed, the belville washer locks the valve cover and the spring carrier together preventing rotation, and at the same time acts on the ball race, pushing it hard up against the balls, locking them half way up the inclined track and compressing the springs.

    As the valve starts to open, the increasing valve spring force cause the belville washer to flatten. The ball race no longer locks the balls in the inclined tracks and therefor the valve cover is free to move. The valve cover now moves over the ball bearings until the balls are at the end of inclined tracks, as the cover rotates, so does the collet and the valve spindle.

    As the valve shuts, the belville washer locks the valve cover to the spring carrier and applies pressure to the ball races as mentioned above and forces balls back up the inclined tracks and locking them up preventing rotation.

    1. Rotocaps stop operating below about 25 % of engine load.
    2. Contaminants in the lube oil which lubricates the valve gear may cause deposits in the inclined tracks and makes the rotocap ineffective..
    3. It should be noted that rotocaps rotate the valve as it opens and not when it closes as it is in the main engine exhaust valve.


    • #3
      Rotocap is used for forced valve rotation. It turns the valve spindle when the valve opens to ensure even heat transfer around the valve seat.

      Increasing load on the valve spring during start of exhaust makes the spring washer flat. The force applied leads the ball to move freely on the inclined tracks. This transfer the reactive force of ball to the spring washer while the reactive force of spring washer to the inner rim of the valve body. Then, the spring-loaded seat and valve assembly rotate to the same degree. As the valve start to close, the Belville washer will lift the ball against the small compression spring. This turns the valve assembly and spring holder to its natural position.