Sea-Doo Rotary Valve Timing & Fixing Guide [Video]

It’s safe to say that the most common problems with Sea-Doo’s rotary valve system are improper timing, lack of lubrication, and the notorious brass gear damage. While timing the valve is a relatively simple task, the latter requires you to disassemble the entire engine and invest in a new valve gear shaft assembly.

Due to its complex design, a Sea-Doo rotary valve is much more prone to failure than the simpler reed valve system.

If you want to find out more about these malfunctions and their fixes, you’ve come to the right place.

We at JetDrift have compiled all you need to know under one roof!

Typical Sea-Doo Rotary Valve Malfunctions

Many things can go wrong on a 2-stroke Sea-Doo engine, and the rotary valve system is no exception.

In a nutshell, the most common problems of this system include:

·         Wrong timing

·         Valve damage

·         Rotary brass gear damage

·         Rotary shaft damage

·         Defective bearings and seals

·         Crankshaft worm gear and seal damage

Let’s get down to the nitty-gritty and talk about these in detail!

How Do You Time the Rotary Valve on a Sea-Doo?

There’s no question that the most common issue of rotary valves is improper timing. This means the opening and closing angles of the rotary valve plate are incorrect in relation to the flywheel side (MAG side) piston.

Are you wondering what the symptoms are of an improperly installed valve?

In a nutshell, if the rotary valve plate is out of time, the engine most likely won’t start, but if it does the engine will typically spit and sputter, or even backfire.

Because of this, correct rotary valve settings are very important for proper engine operation.

How do you set the timing on a rotary valve Sea-Doo engine?

In a nutshell, you have to set the opening and closing angles of the rotary plate. For this process, you will need two dedicated tools, a timing wheel (a.k.a. Degree Wheel) and a Top Dead Center (TDC) gauge.

To set the correct timing, you have to find the top dead center of the flywheel piston (a.k.a. MAG side piston). This is the position where the piston stops at the very top of the cylinder.

Best practice is to use a dedicated tool for this purpose, known as the Top Dead Center gauge. If one is not available, you can also figure out where the top dead center is manually, using a marker.

Just hold a marker against the flywheel piston and rotate the crankshaft back and forth until you find the TDC point.

This can be tricky without the gauge, but not at all impossible.

(Note: Once you have the TDC point, it’s very important not to rotate the crankshaft or the valve shaft during further operations.)

Then, install the timing wheel on the rotary shaft to mark the BTDC degree on the side of the engine with a marker. The zero mark of the wheel has to be aligned with the bottom of the zero port.

Remove the timing wheel and install the valve plate, leaving the front port open. The top edge of the valve plate should match your mark.

If it doesn’t fit in any way you should flip the plate since it has an asymmetrical design.

The good news is that installing a rotary valve is not rocket science, since the factory tolerance here is +/- 5 degrees.

Therefore, you shouldn’t worry if you can’t align the valve plate exactly to the mark because it will work if the difference is not more than 5 degrees.

If you want to find out more, here is a step-by-step tutorial of the process from beginning to end:

This procedure is the same on all Sea-Doo rotary valve engines, except for the angles, which are as follows:

Sea-Doo Rotary Valve Timing Chart

(This chart is for informational purposes only. For exact specifications please refer to your ski’s service manual.)

How Do You Replace a Rotary Valve on a Sea-Doo?

If the valve plate is corroded, bent, worn, or heavily scratched it’s time to replace it.

When it comes to Sea-Doo rotary valve replacement, note that there’s no identification on the different valves for some reason.

Therefore, you have to make sure to purchase the right valve plate for your ski. To ensure the fit, you can find a template in the service manual that displays the actual size of the valve.

Once you have the right-sized replacement unit, you can replace it using these simple steps:

1.       Remove the rotary valve cover

2.       Remove the old valve plate

3.       Set the timing (as described above)

4.       Apply a little 2-stroke oil on both sides of the plate

5.       Install the new valve plate

6.       Install O-ring and cover

7.       Torque screws to 20N•m (15 lbf•ft)

Brass Gear Damage and Fixes

Besides incorrect timing, another common problem with the rotary valve system is brass gear damage. This gear is mounted on the rotary valve shaft designed to take off the power from the crankshaft.

Often referred to as the rotary valve brass gear, this is a helical gear, meaning that its teeth are angled to the axis of its rotation.

This is no surprise since it connects to a worm gear, which is mounted on the center of the crankshaft.

Designed to be a sacrificial component, the rotary valve gear is made of brass, which is softer than the crankshaft-mounted worm gear.

The main idea behind this brass-to-steel design is to protect the more valuable steel components from damage. In case of a malfunction, the brass gear on the rotary valve shaft sacrifices itself to save the steel worm gear on the crankshaft.

It’s a common issue that the brass gear gets stuck due to lack of lubrication and the worm gear completely eats it.

Since the rotary valve shaft is removable, it looks like all you have to do is pull it out and replace the brass gear on it. Unfortunately, the situation is not that simple!

General wisdom says that if the brass gear has suffered any damage, the engine has to completely be pulled out and taken apart.

This is necessary because you have to clean all of the brass shavings from the rotary valve chamber and the crankshaft.

If a little brass is leftover from the old gear and smeared on the worm gear, it would destroy the new brass gear in a couple of hours of running.

But the bad news doesn’t end there.

If the brass gear gets damaged, in most cases it bends the rotary valve shaft. Note that only an extremely small deformation in the shaft can eat the new brass gear in a short time.

Keeping safety in mind, you have to replace it with an entire rotary shaft assembly including the brass gear, the bearings, and the seals. Therefore, it can often be purchased as an assembled unit.

On top of that, sometimes the brass debris damages the rotary valve shaft seals on the crankshaft.

It’s also good to know that when the brass gear gets damaged, it typically moves the worm gear away from its centered position. Since this gear has to be precisely centered on the crankshaft, the entire crankshaft needs to be inspected.

In summary, if the brass gear in your rotary valve system is stripped, you have to proceed with the following steps:

(Step zero: Find and fix the root cause of the failure!)

1.       Pull the engine

2.       Remove the rotary valve cover and the valve plate

3.       Remove the rotary valve shaft (This can be tricky, so we’ll talk about it later)

4.       Take the engine and the crankshaft apart

5.       Flush and clean the brass shavings from the rotary valve shaft chamber

6.       Inspect, clean, and center the worm gear on the center of the crank

7.       Inspect the rotary valve shaft seals on the crank (and replace them if necessary)

8.       Assemble the engine

9.       Install a new complete rotary valve shaft assembly (including the bearings and the gears)

10.   Reassemble the rotary valve as described above

Note that the only way to clean the engine and check the worm gear and the seals on the crankshaft is to pull the engine and take it apart, no quick fixes here.

Another thing to consider is that the brass gear doesn’t just break for no reason.

Before you assemble the engine with the new components, it’s highly recommended that you investigate the root cause of the failure.

If this does not happen, the existing malfunction will more than likely destroy the new parts as well.

In most cases, the root cause of brass gear damage is insufficient lubrication.

The entire shaft assembly is nestled in the rotary valve shaft chamber, which has to be filled full of oil. If there are dry spots on the assembly or anywhere inside the chamber it’s a sign of poor lubrication.

Note that the valve shaft assembly is lubricated with 2-stroke engine oil, but it isn’t fed by the oil pump.

Instead, this shaft assembly has a gravity-feed oil system featuring two small oil lines connected to the bottom of the engine.

These lines are prone to clogging, cracking, or falling off, causing oil starvation.

However, the rotary valve seals on the crankshaft can also be worn out. Defective seals can not only leave the gears without lubrication but they also allow the oil to leak into the crankcase.

In the worst-case scenario, this may result in a hydrolocked engine.

Rotary Valve Shaft Removal

As we’ve discussed, you have to replace the entire rotary shaft assembly to avoid future damage.

The problem with this is that this shaft is often stuck into the engine.

This is where the Sea-Doo Rotary Shaft Puller comes into play. This purpose-built tool is designed to pull the shaft out without any effort. Just remove the valve cover, the valve plate, and a snap ring, and then pull the shaft.

If you don’t want to invest in this tool, here’s a great DIY alternative (but you can also use a big socket):

Rotary Valve Lubrication vs. Premix

As we’ve discussed, the rotary valve shaft assembly is lubricated with a separate oil system that cannot be eliminated.

If you have a rotary valve Sea-Doo and want to switch to premix, it’s very important not to remove the oil tank from the ski.

Also, make sure not to remove the oil lines coming from the tank to the rotary shaft cavity.

One of these lines delivers oil from the oil tank and the other is a vent line.

Finally, don’t forget to check the oil level in the tank and refill it occasionally.

While this is obvious as long as the entire engine is lubricated from the oil tank, it’s easy to forget about it once you’ve switched to premix.

Conclusion

The rotary valve can be easily timed using a timing wheel.

Just find the top dead center of the flywheel side (MAG side) piston and mark the right angle on the side of the engine using the timing wheel.

Then, fit the valve plate to the mark and finally install the valve cover. The key is not to move the crankshaft during the entire process to keep the flywheel piston in TDC position.

The rotary valve is driven by the rotary valve shaft, which is actually an assembly of 12 different components. It runs in an oil bath and is nestled in the rotary shaft chamber, which is separately lubricated from the oil tank.

Only a small malfunction in this oil system or a damaged seal can leave the rotary shaft without lubrication, which typically ends in brass gear damage.

Sitting on the rotary shaft, this helical gear attaches to the crankshaft via a worm gear. 

Designed as a sacrificial item, this brass gear is the most frequently damaged component on the rotary shaft assembly.

In case of brass gear damage, the entire engine has to be taken apart to remove brass debris from the chamber and the worm gear.

When the brass gear gets damaged, it nearly always bends the valve shaft, even if only a small extent.

This little deformation will eat the new brass gears every time, which is a common issue with these engines. Consequently, the entire rotary valve shaft assembly has to be replaced, not just the brass gear.

So, to sum it up, no matter how the brass gear is damaged in a rotary valve Sea-Doo, its engine has to be taken apart and cleaned of all brass shavings. Then, a new complete rotary shaft assembly has to be installed.

Last but not least, the root cause of the malfunction has to be identified to avoid similar problems in the future.