What Is a Rotocap and How Does It Work?

As exhaust valves are expected to withstand high temperatures and soot, this can lead to valve seizure, heavy soot deposits, and overheating. Luckily, rotocaps can be utilized to protect exhaust valves from such concerns. In this blog, we will outline the importance of rotocaps in a wide range of applications, but especially their use in conjunction with valves.

Generally, a rotocap is fitted on exhaust valves found in auxiliary or medium-speed engines. That being said, rotacaps are simple devices used for forced valve rotation, often finding use in the automobile industry for vehicles with high power and low speed. However, main engines are usually equipped with rotating vanes instead of rotocaps to help them rotate.

In engines, a rotocap turns the valve spindle during the opening of the valve to provide even heat transfer around the valve seat. As such, it helps avoid local hot-spots, pitting, and distortion as a result of uneven heating. More than that, a rotocap helps mitigate abrasive wear and soot deposits on the valve seat and valve guide.

By rotating the valve 8 degrees on each operation, rotocaps avoid the  uneven or unintentional rotation of exhaust valves, increasing their overall service lives in the process. Additionally, they prevent exhaust valves from “burning.” When heavy soot deposits on the valve seat due to rotocap malfunction, the exhaust valve stops to seat properly, allowing the hot gas to move through the valve face with ease.

Burning can also lead to overheating which may weaken the valve material. The weakening of the valve material can produce a chain reaction wherein more and more gaps for gas to seep through are created. This type of damage is usually only detected once you experience high exhaust temperatures followed by power loss.

How Is a Rotocap Constructed?

In terms of construction, a rotocap is a self-contained assembly composed of balls and ramps. It is considered a positive type of valve rotor structure that features a valve plate with six slots for the balls to roll in. Each slot has a separate set of springs and balls placed into it, and each ball is compressed by these springs. When the valve is in a closed position, the spring washer locks the spring carrier and valve cover together.

The balls are free to move over the grooves when the valve is in a closed position. The ball races function as a path for these balls to move as the spring sits against the edge of the rotocap. Lastly, the rotocap is constructed to keep the valve rotor when the retaining rings are removed.

How Does a Rotocap Work?

Increasing load on the valve spring during the opening of the exhaust valve makes the spring flatten out. The force applied on the balls within the race allows the ball to move freely on the inclined tracks. This transfers the reactive force of the ball to the spring, while the reactive force of the spring transfers to the inner edge of the valve body.

At the same time, the spring-loaded seat and valve assembly rotates to the same degree, ensuring that the spring washer, valve spring, ball race, and collar are secured together with a friction grip. As the valves begin to close, the spring washer returns to its original position, lifting the ball against the small compression spring, and turning the valve assembly and spring holder to its starting position so that the balls no longer move.

How Are Rotocaps Maintained?

When preventative maintenance is carried out on a cylinder head, all the individual components in the assembly must be dismantled and checked for cracks or damage. This must also be performed on all valves, the cylinder head seat, guides, and valve springs. If a rotocap is featured, it must be stripped, cleaned, and inspected. For irregularities or defects, replace the rotocap immediately. You should also renew all springs, clean all tracks, and check the condition of the balls.


Purchasing 3sixty is a leading supplier of rotocaps in the aviation industry. We also carry an array of other top-quality items, ensuring that customers from all industry verticals can meet their operational requirements. Get started today and see how Purchasing 3sixty can serve as your strategic sourcing solution!


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