Complete Shaft & Bushing Guide

Introduction

If your BMW R1100S rattles at idle, refuses to synchronize properly or develops an unstable idle, worn throttle body bushings are one of the most common causes.

The original bronze bushings gradually wear over time. Once the throttle shaft develops play, the throttle body can begin drawing false air, making synchronization difficult and causing the familiar “marbles in a tin can” rattle that many Oilhead owners know all too well.

This guide documents a complete rebuild using a shaft and bushing kit from Custom Skunk Garage.

▶ Watch the throttle body rebuild video

If you’d like to see the entire rebuild before getting started, this excellent video walks through the complete process step by step.

Symptoms of Worn Throttle Bodies

Typical symptoms include:

• Metallic rattling at idle
• Idle changes after synchronization
• Difficult throttle body balancing
• False air entering around the shaft
• Hesitation just off idle
• Uneven idle speed

If you can move the throttle shaft sideways by hand, the bushings are almost certainly worn.

Parts Required

The rebuild kit used here includes:

• Bronze bushings
• New throttle shaft
• Shaft seals
• O-rings
• Butterfly screws
• Small hardware

The kit shown was purchased from Custom Skunk Garage for approximately €150.

Tools Required

• Torx drivers
• Small screwdrivers
• M10 tap
• Tap wrench
• Small hammer
• Fine file or Dremel
• Threadlocker
• Carburettor cleaner
• Assembly grease

Step 1 – Remove the Butterfly Valve

The butterfly screws are staked from the factory.

Before attempting removal, carefully file or grind away the peened end of each screw.

Trying to remove them without doing this can easily damage the shaft threads.

Once the screws are removed, the butterfly plate lifts out.

Step 2 – Strip the Throttle Body

Disassemble the throttle body completely.

Remove:

• butterfly plate
• shaft
• return spring
• washers
• seals
• bushings

Lay every component out in order. It makes reassembly considerably easier.

Step 3 – Removing the Bushings

This is usually the hardest part.

The bronze bushings are often seized tightly inside the housing.

Ole Ejs found an elegant solution:

Thread an M10 tap into the bushing and use it as a puller. Once engaged, tap the tool from the opposite side and the bushing comes out surprisingly easily without damaging the throttle body housing.

This trick alone can save hours of frustration.

Step 4 – Install the New Bushings

Lubricate the new bushings lightly before installation.

Press them squarely into the housing.

Never hammer directly on the bronze surface.

Take your time. Proper alignment is critical for smooth shaft movement.

Step 5 – Install the New Shaft and Seals

Install:

• shaft
• seals
• spring
• spacers
• washers

The shaft should rotate freely without noticeable side play.

If anything binds, stop and investigate before continuing.

Step 6 – Butterfly Alignment

This is probably the most critical step of the entire rebuild.

Close the throttle completely.

Hold the butterfly plate firmly against the bore while tightening the screws.

After tightening, hold the throttle body against a bright light.

You should see virtually no light around the edges of the butterfly.

If light is visible, loosen the screws and repeat the alignment.

Final Assembly

Apply a small amount of threadlocker to the butterfly screws.

Reinstall the throttle body on the motorcycle.

Reconnect all hoses and cables.

Finally perform a complete throttle body synchronization.

Results

After the rebuild:

• Idle rattle disappeared
• Air leaks were eliminated
• Idle became noticeably smoother
• Synchronization became easier and more stable

In Ole’s case, the worn bushings had developed enough play to allow false air into the engine. Replacing both the shaft and bushings solved the problem completely.

Frequently Asked Questions