You could say the mufflers on the Honda CB450 are cursed. They are often rusted through, missing, or replaced with an ill-fitting aftermarket exhaust. While our replacement mufflers are not factory clones, they retain a period-correct look and can be installed cleanly with the correct hardware, bracket setup, and gaskets.

Why these mufflers work so well on the Honda CB450

Original Honda mufflers are incredibly difficult to find in usable condition. Even when an aftermarket muffler physically fits, the appearance, mounting arrangement, and effect on engine tuning may not be ideal. These mufflers are sized appropriately, sound great, and look correct on the CB450 family of motorcycles. They also use fully mechanical baffles that are removable, which makes future cleaning or repacking possible.

Parts Needed

• Pair of Common Motor mufflers
• Muffler mounting hardware - Comes with the Common Motor mufflers
• Stainless T-bolt clamps - Comes with the Common Motor mufflers
• Copper crush gaskets for header pipe to cylinder head
• Four aluminum beverage cans for making the header pipe to muffler gaskets
• Anti-seize compound
• Red thread locker
• 3/4 inch automotive heater hose
• Clear nail polish, paint, or another rust-preventive coating for modified bracket edges
• Painter's tape

Tools Needed

• Metric hand tools
• Flathead screwdriver
• File
• Round file
• Hacksaw
• Step drill bit
• Adjustable wrench
• Utility knife or hobby knife
• Scissors
• Marker
• Ruler or caliper
• Pliers

What hardware is included with the mufflers

Optional Recommended Parts

The original Honda muffler connection uses a graphite-style gasket, but that gasket is too large to fit these replacement mufflers correctly on the CB450. The stepped metal adapter collars supplied with the universal mufflers also do not provide the fit Common Motor prefers on this application.

For the CB450 installation shown here, the muffler-to-header seal is made from two layers of thin aluminum sheet wrapped around each header pipe.

Note: The aluminum sleeve gasket should be considered single use.. If the joint is separated later, plan to remake the gasket before reassembly.

Inspecting and servicing the removable baffles

These mufflers use a removable mechanical baffle. While we find the mufflers sound good in their standard configuration, additional packing can be added if a quieter exhaust note is desired.

Baffle service notes

• Remove the baffle carefully by removing the 3 Allen head bolts.
• Clean carbon or debris from the baffle before reinstalling it.
• Additional muffler packing can be added if a quieter exhaust note is desired.
• Use anti seize compound on the bolts before reinstalling them into the muffler. Make sure the baffle is securely reinstalled before operating the motorcycle.
• Do not over tighten the Allen head bolts and strip the internal threads.

Mounting the Mufflers on the CB450

Reusing the factory CB450 muffler brackets

The factory brackets, used in conjunction with the included universal brackets, are the preferred option when they are still available because they provide a stronger 2 mounting points to the back of the mufflers.

The CB450 brackets are left- and right-side specific and must be installed in the correct orientation.

For the left-side muffler shown in the installation, the flatter and more vertical side of the bracket faces the rear of the motorcycle. The more angled portion faces the front. The two muffler mounting holes sit farther inward toward the tire, while the larger frame mounting hole sits farther outward.

Universal bracket modification steps

The recommended hardware arrangement combines the factory bracket with the universal chrome strap supplied with the mufflers. Special square nuts fit inside the muffler mounting channel and provide a broad mounting surface for the hardware.

1. Number the universal bracket holes from 1 through 6 as shown in the video.
2. Hole 5 is approximately 10mm in diameter. It will need to be elongated by 5mm towards hole 6.
3. Use a round file to to file the hole until it is 15mm in total length.
4. Check that the bracket is filed enough by aligning the front hole of the factory bracket with hole 2 and the rear with the newly filed hole 5 of the universal bracket.
5. Repeat this process for both universal brackets for both mufflers.
6. Seal all exposed raw metal edges with clear nail polish, paint, or another protective coating.

Factory bracket hardware arrangement

Important installation note

Mock up the bracket loosely first. Exhaust systems on vintage motorcycles often require slight movement because header pipes, frame tabs, brackets, and previous repairs may not be perfectly aligned after years of use. Apply red threadlocker after the entire system is aligned on the motorcycle and you are committed to the final position.

Using only the included universal brackets

If the factory brackets are missing, the included universal chrome strap brackets can be modified into a solid setup using a few simple hand tools.

Universal bracket modification steps

1. Number the universal bracket holes from 1 through 6.
2. Mark the cut location between holes No. 4 and No. 5.
3. Use a file to notch the chrome surface where the hacksaw cut will begin.
4. Cut the bracket with a hacksaw.
5. Deburr the cut edges and round the corners with a file.
6. Enlarge hole No. 1 with a step drill bit so the frame mounting fastener fits as shown in the installation.
7. Deburr the drilled hole.
8. Seal all exposed raw metal edges and drilled surfaces with clear nail polish, paint, or another protective coating.

Universal bracket modification measurements

Note: This is the best option for mounting the mufflers with the universal bracket and basic hand tools. However, if you own more advanced tools then a better custom mounting bracket can be made.If you own a welder, we would recommend welding the 2 cut pieces of the bracket together once they are positioned in the proper position on the motorcycle.  This will create a much more solid 2 point bracket.

Modified universal bracket orientation

• Install the short cut section against the muffler mounting channel.
• Install the longer bracket section so it extends upward toward the frame mounting point.
• Use two attachment points at the muffler mounting channel.
• Keep the bracket hardware loose enough to slide during initial alignment.
• Position the enlarged hole at the frame mounting point.

Why the square nuts matter here

The modified universal bracket benefits from the same square nut arrangement used with the factory bracket. The square nuts provide a larger footprint inside the muffler mounting channel and help the mounting hardware grip the channel more securely.

Header pipes and exhaust gaskets

Before fitting the mufflers, inspect the header pipes and replace any worn sealing parts.

Preparing the cylinder head connection

1. Inspect the cylinder head exhaust port for the old copper crush gasket.
2. Use a small flathead screwdriver or pick to carefully remove the old gasket if it is still in place.
3. Check again to make sure a second old gasket is not hidden underneath the first.
4. Install a fresh copper crush gasket.
5. Reinstall the header pipe and exhaust collars.
6. Position the belled section of the exhaust collars facing outward.
7. Lightly snug the header fasteners until the pipe begins to seat.
8. Leave enough movement in the header pipe for final exhaust alignment.

Caution: Do not continue tightening the header fasteners simply because the gasket continues to compress. Snug the connection enough to seat the pipe, then leave the system slightly loose until the muffler is aligned.

Preparing the header pipe

The replacement mufflers fit over the existing CB450 header pipes, but the original graphite-style muffler gasket is too large for this replacement muffler inlet. The universal metal adapter collars supplied with the mufflers also do not fit the tight CB450 header pipe clearance. Instead, two layers of aluminum sheet are wrapped around each cleaned header pipe to create the required muffler-to-header sleeve gasket.

1. Clean carbon, old gasket material, and residue from the muffler end of the header pipe.
2. Cut four sheets of aluminum from beverage cans.
3. Trim each sheet to approximately 45 mm wide.
4. Wrap one aluminum sheet tightly around the header pipe.
5. Hold the aluminum temporarily with painter's tape.
6. Wrap a second aluminum sheet over the first layer.
7. Pull the second layer tight and secure it temporarily with painter's tape.
8. Repeat the process on the opposite header pipe.
9. If the muffler end is slightly too small, gently open the slots on the end with an adjustable wrench so the muffler can slide on smoothly.

Aluminum gasket dimensions

Note: The painter's tape is only used to hold the aluminum in place during assembly. The tape will burn away after the exhaust reaches operating temperature.

How to install the mufflers with factory brackets

1. Loosely install the header pipe at the cylinder head with the exhaust collars and nuts.
2. Wrap two 45 mm-wide aluminum gasket layers around the cleaned header pipe.
3. Place the stainless T-bolt clamp over the muffler inlet.
4. Apply a small amount of anti-seize to the clamp threads and the clamp seat.
5. Slide the muffler onto the header pipe without disturbing the aluminum gasket.
6. Align the end of the muffler with the stop ring on the header pipe.
7. Do not slide the muffler past or over the stop ring as it will prevent the muffler from clamping the aluminum gasket fully.
8. Install the frame mounting bolt through the factory bracket and leave it slightly loose.
9. Adjust the muffler position, bracket position, and clamp position until the system sits naturally.
10. Snug the T-bolt clamp.
11. Snug the header fasteners at the cylinder head.
12. Tighten the frame mounting hardware.
13. Tighten the bracket-to-muffler hardware evenly.
14. Once satisfied with fitment, remove one bracket bolt at a time, apply red threadlocker, and reinstall.

T-bolt clamp positioning

For this CB450 setup, the T-bolt clamp should be clocked so the bolt faces upward.

On the left side of the motorcycle, check the clamp position carefully against the shift lever. The shift lever shown in the installation sits approximately level with the foot peg, and the clamp must be positioned so the lever can move without interference.

How to install the mufflers with modified universal brackets

1. Loosely install the header pipe at the cylinder head.
2. Wrap the two aluminum gasket layers around the cleaned header pipe.
3. Place the T-bolt clamp on the muffler.
4. Slide the muffler onto the header pipe.
5. Align the muffler inlet with the stop ring on the header pipe.
6. Do not slide the muffler past or over the stop ring as it will prevent the muffler from clamping the aluminum gasket fully.
7. Position the modified universal bracket on the back side of the factory frame mounting point.
8. Install the frame mounting bolt and nut loosely.
9. Adjust the bracket position and rotation until the muffler sits square on the motorcycle.
10. Move the bracket within the muffler mounting channel as needed to raise or lower the rear of the muffler.
11. Snug the T-bolt clamp.
12. Snug the header nuts.
13. Snug the frame bolt.
14. Make any needed adjustments before final tightening.
15. Apply red threadlocker to the bracket bolts only after the final position is confirmed.

Foot peg clearance note

The foot peg assembly must be removed during the installation to provide access to the muffler clamp and mounting area.

When reinstalling the foot peg, pay close attention to the orientation of the nearby mounting hardware. The installation shown positions the relevant bolt upward because there is not enough clearance below the foot peg for the bolt in the opposite orientation.

Final tightening, alignment, and service notes

Once the muffler, header pipe, bracket, and clamp are all in the correct position, tighten the entire system evenly.

This is the stage where final threadlocker can be applied to the bracket bolts.

Final checks

• Muffler is seated correctly before the stop ring
• Aluminum gasket is captured completely inside the muffler inlet
• Clamp is centered and properly rotated so it does not interfere with the shifter or foot peg
• Header pipe is sealed at the cylinder head
• Muffler bracket is not under tension
• Muffler sits at the desired height and angle
• Muffler bracket does not slide in the mounting channel
• Foot peg hardware is installed with adequate clearance
• All hardware is tightened evenly

Important future service note

If the exhaust assembly needs to come off later, remove the muffler and header pipe assembly from the motorcycle as one piece when possible. Remove the large frame bolt that connects the muffler hanging bracket and the header exhaust flange nuts to pull the exhaust system off as a single piece.

Do not separate the muffler from the header pipe unless you are prepared to remake or replace the aluminum sleeve gasket.

How to protect the mufflers from stand contact

The factory mufflers used built-in stand bumpers. These replacement mufflers do not. Without protection, the side stand and center stand can strike the muffler and leave dents or marks over time.

A simple solution is to slide short sections of 3/4 inch automotive heater hose over the contact points on the stands.

Heater hose bumper lengths shown in the video

Use tire lube, soapy water, or a similar lubricant to slide the hose into place.

The hose is a wear item. When it eventually wears out, cut it off and replace it with another section.

Troubleshooting

The muffler will not slide onto the header pipe

Clean the pipe end thoroughly and make sure the aluminum gasket is wrapped tightly. If the muffler end is slightly compressed, gently open the slotted inlet with an adjustable wrench just enough for the muffler to slide on.

The muffler joint leaks

Verify that both aluminum gasket layers are installed and that the muffler has not been pushed over the stop ring. Recheck the clamp position and clamp tension.

The T-bolt clamp may need to be tightened more than expected before the muffler becomes secure.

The muffler does not line up with the frame mount

Loosen the entire system again. On vintage exhaust systems, the header pipe, muffler, and brackets often need to float into position before final tightening.

Adjust the muffler bracket in small increments until the muffler sits naturally.

The header pipe leaks at the cylinder head

Remove the header and inspect the exhaust port for an old crush gasket.

Old copper gaskets can become heavily compressed and covered with carbon, making them difficult to see. The motorcycle shown during the installation had two old gaskets stacked together because a previous installer had installed a second gasket without removing the first.

Remove all old gasket material before installing one fresh crush gasket.

FAQ

Can I reuse the factory muffler mounting brackets on a Honda CB450?

Yes. The factory brackets are the preferred option when they are still available. They are left- and right-side specific and are used together with a modified universal chrome strap in this installation.

What is used instead of the factory graphite muffler gasket?

This CB450 installation uses two layers of approximately 45 mm-wide aluminum beverage-can sheet wrapped around each header pipe.

Can I remove the baffles from these mufflers?

Yes. The mufflers use removable mechanical baffles that can be cleaned or repacked if desired.

Can I separate the muffler from the header pipe later for service?

You can, but it is not recommended once the joint has a good seal. Remove the muffler and header pipe together as one assembly when possible.

Will I need to rejet the carburetors after installing these mufflers?

Possibly. Anytime the intake, air filter, or exhaust system is changed, carburetor jetting may need to be adjusted to compensate for the change in airflow. Final carburetor tuning should always be based on how the individual motorcycle runs with its complete intake and exhaust setup.