Replacing the Catalytic Converter

Many BMW R1100S owners replace the original catalytic converter with a Y-pipe, often referred to as a cat delete.

The modification removes the large collector box beneath the motorcycle and replaces it with a simpler Y-shaped pipe that connects the headers directly to the silencer.

The result is a cleaner exhaust layout, a modest weight reduction and a deeper, more purposeful exhaust note. The sound remains civilised with the original silencer, but gains a little more character—exactly what many riders are looking for.

Disclaimer

⚠️ Important

Replacing or removing the catalytic converter may not be legal in your country.

Before carrying out this modification:

• Check your motorcycle’s type approval.
• Verify your local emissions and roadworthiness regulations.
• Ensure the modification complies with the laws where the motorcycle will be used.

This guide describes the mechanical installation only and does not imply that the modification is road legal in your jurisdiction.

Parts Required

• Y-pipe
• Existing silencer
• Existing lambda (oxygen) sensor
• Original exhaust gaskets (reuse if in good condition)

Tools Required

• Torx sockets
• Socket set
• Ratchet
• Oxygen sensor socket or suitable open-ended wrench
• Penetrating oil (recommended)
• Copper grease (optional)

Preparation

As with most work on the R1100S, all work begins with removing the side fairings.

Although it is possible to complete the installation with the rear wheel fitted, we removed it to create additional working space.

Step 1 – Remove the Catalytic Converter Support

Locate the support bracket underneath the catalytic converter.

Remove the two rear mounting bolts securing the bracket to the motorcycle.

Step 2 – Disconnect the Header Pipes

Undo the fasteners connecting the left and right header pipes to the catalytic converter.

Leave the headers supported.

Do not force anything.

Step 3 – Loosen the Silencer Clamp

Loosen the exhaust clamp connecting the catalytic converter to the silencer.

The silencer does not need to be removed completely.

Just allow enough movement for the catalytic converter to slide out.

Step 4 – Remove the Lambda Sensor

This is often the most difficult part of the entire job.

Rather than attempting to unscrew the sensor while it is still connected electrically, disconnect the sensor from the motorcycle first and remove it together with the catalytic converter.

Otherwise the cable will twist excessively as the sensor turns.

Some sensors can be very tight after years of heat cycles.

Don’t be surprised if considerable force is required to loosen it.

Step 5 – Remove the Catalytic Converter

Carefully slide the catalytic converter rearwards and remove it from the motorcycle.

Pay particular attention to the copper sealing gaskets at the header pipe connections.

These should remain in place and should not be damaged during removal.

If they are worn or deformed, replace them.

Step 6 – Install the Lambda Sensor in the Y-Pipe

Transfer the lambda sensor to the new Y-pipe before fitting it to the motorcycle.

This is considerably easier than trying to install it afterwards.

Step 7 – Install the Rubber Mounts

Fit the two rubber bushings onto the mounting pins of the Y-pipe.

These isolate vibration and support the pipe inside the frame bracket.

Step 8 – Assemble Everything Loosely

Offer the Y-pipe into position.

Insert the rubber-mounted locating pins into the frame bracket.

Reconnect:

• both header pipes
• silencer connection

Leave every clamp and fastener loose at this stage.

This allows the exhaust to self-align before final tightening.

Step 9 – Final Tightening

Tighten the system in this order:

1. Alternate between the left and right header pipe fasteners until both are fully seated.
2. Tighten the silencer clamp.
3. Reconnect the lambda sensor wiring.

Following this sequence helps minimise stress in the exhaust system.

Final Checks

Before refitting the fairings:

• Start the engine.
• Listen carefully for exhaust leaks.
• Verify the lambda sensor cable is routed safely.
• Ensure nothing touches the swingarm or rear wheel.
• Check that all fasteners are fully tightened after the first heat cycle.

Results

The modification produces several noticeable changes:

• Slightly deeper exhaust note.
• Reduced weight compared with the original collector box.
• Simpler exhaust system.
• Improved access beneath the motorcycle for future maintenance.

With the original silencer, the increase in sound is noticeable but not excessive, giving the R1100S a slightly more sporting character without becoming intrusive.

Frequently Asked Questions