How a Rotocap Works How a Rotocap Works

The rotocap is a mechanical means to rotate a valve The rotocap is a mechanical means to rotate a valve during operation. during operation.

Usually fitted to exhaust valves, rotation of the valve Usually fitted to exhaust valves, rotation of the valve ensures that the valve is kept at an even temperature so ensures that the valve is kept at an even temperature so it does not distort and leak by, and it helps  dislodge any it does not distort and leak by, and it helps  dislodge any build up of deposits on the valve and seat.build up of deposits on the valve and seat.

The valve cover has an number of  inclined tracks The valve cover has an number of  inclined tracks machined into it, each containing a ball and spring. The machined into it, each containing a ball and spring. The balls run on a race; When the valve is closed, the belville balls run on a race; When the valve is closed, the belville washer locks the valve cover and spring carrier together, washer locks the valve cover and spring carrier together, preventing rotation, and at the same time acts on the ball preventing rotation, and at the same time acts on the ball race, pushing it hard up against the balls, locking them race, pushing it hard up against the balls, locking them half way up the inclined track and compressing the half way up the inclined track and compressing the springs.springs.

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

As the valve shuts, the belville washer locks the As the valve shuts, the belville washer locks the valve cover to the spring carrier and applies valve cover to the spring carrier and applies pressure to the ball race which forces the balls pressure to the ball race which forces the balls back up the inclined tracks. back up the inclined tracks.

Rotocaps stop operating below about 25% engine load. Rotocaps stop operating below about 25% engine load. Contaminants in the lub.oil causing deposits in the inclined tracks  Contaminants in the lub.oil causing deposits in the inclined tracks  will stop the rotocap from working. Continued operation will then will stop the rotocap from working. Continued operation will then cause indentations in the tracks by the balls, which will render the cause indentations in the tracks by the balls, which will render the rotocap beyond repair. rotocap beyond repair.

It is normal to mark the top of the rotocap with a blob of paint so that It is normal to mark the top of the rotocap with a blob of paint so that it can be easily seen if they have stopped rotating. If this is the case, it can be easily seen if they have stopped rotating. If this is the case, then they should be changed as soon as possible and overhauled.then they should be changed as soon as possible and overhauled.

It should be noted that rotocaps rotate the valve as it opens. It should be noted that rotocaps rotate the valve as it opens. Although this will prevent distortion due to uneven temperatures, it Although this will prevent distortion due to uneven temperatures, it does not lend itself to removing the build up of deposits on the does not lend itself to removing the build up of deposits on the seating faces. A device known as the "seating faces. A device known as the "Turnomat" which turns the " which turns the valve as it closes is more suited to that.valve as it closes is more suited to that.