The Ultimate Guide To Dirt Bike Exhausts
Repacking your muffler is a quick and easy process, and if you do it often enough, it isn’t even a messy job! Follow this how-to guide on muffler repacking to ensure your bike always passes emissions tests on race days and avoid being 'that person' with a bike that sounds like you are banging an old fuel can with a cricket bat!
Why should you repack your dirt bike muffler?
For starters, more and more tracks are being closed or restricted due to noise complaints, so turning up to your favourite place to ride with an excessively noisy machine will just inflame any issues. Secondly, dirty packing will restrict the flow of exhaust from your motor which as a result will rob your bike of power. If you have just spent money on a performance exhaust but fail to keep the muffler packing fresh, you may as well have not even bought the pipe in the first place!
How often should you repack your dirt bike muffler?
The Yoshimura factory suggests repacking off-road systems every 10-15 hours to maintain peak performance. Muffler packing will deteriorate particularly quickly on two-stroke mufflers machines as the addition to oil to the fuel being burnt produces more carbon which chokes a bike even quicker.
How to repack a dirt bike exhaust:
Repacking a muffler is actually an easy and simple process, especially if you keep on top of regularly maintaining your exhaust pipe.
The first step involves removing the muffler from your bike and assessing whether its bolted together, or held together by rivets. If it's held together by rivets only, you'll need to drill these out - you'll need to rivet it back together at the end, so keep that in mind. If it's bolted together, simply undo the bolts.
If it's a 2-stroke silencer, you'll need to remove the screws at the bottom of the muffler - you shouldn't have to drill any rivets out at the tail end, as the baffle and packing can be removed easily from the opposite end.
If it's a 4-stroke, it's an easier process the remove the end cap of the muffler go from there.
To make things easier when pulling the muffler or silencer apart, use a knife or blade to cut the silicone seal on the muffler, and you may also need a rubber hammer to tap against the muffler bracket to help in separating them. Ensure you don't damage the exhaust when you're doing this, so take it easy and be patient.
Once the muffler is separated, remove the baffle and ditch the old muffler packing in the bin. The muffler packing can irritate your skin, so it's a good idea to wear gloves.
Next up is cleaning and inspecting the baffle for damage - check for cracks and any damage, and if you find anything, get it repaired or replaced to ensure the exhaust flow won't be impacted at all.
To clean the carbon from the muffler, you can use a high strength degreaser or you may require a high-pressure bead blaster if the carbon is severely built up.
With a 2-stroke silencer, it's easy to wrap the baffle in the packing material nice and firmly, using a small amount of masking tape to keep everything in place before reinserting it into the silencer.
For the best results on both 2-stroke and 4-stroke dirt bikes, the muffler packing should be firmly fitted to the metal structure of the exhaust. There should not be any free space inside the muffler canister as it will promote increased noise.
When putting the silencer or muffler back together, the packing should be filling the canister space so that it's a snug fit, but it shouldn't be so firm that you need to use heavy force to put it together again.
For four-stroke machines, a common method is to insert the baffle back into the outer chamber and add the packing material after that. Some muffler packing has a woollen finish so it is not as easy to roll it up like a sheet.
Again you want the muffler to be packed firmly inside the entire muffler so use something to assist packing the material down all the way inside the chamber.
After the muffler is completely packed, use a knife to trim any excess packing away for a neat finish. Press the muffler together and ensure the bolt or rivet holes line up.
Replace the screws or rivets, and then reseal the muffler with a heat resistant silicone sealant. It's now time to put the muffler back onto your dirt bike, ensuring all parts of your bike are tightened to the correct torque settings.
How does a dirt bike exhaust work?
A dirt bike exhaust system essentially has three uses: to guide exhaust gases away from you, to reduce or muffle noise, and to increase or alter the performance of your bike. Exhaust systems generally come in two or three sections, made up of the header pipe, mid-pipe, and muffler.
The design, length and routing of a header pipe and muffler changes the way exhaust gases escape, which results in either a smoother or more aggressive power delivery, depending on how these three factors are configured.
Exhaust manufacturers develop each system for every dirt bike they cater for, where they achieve the perfect balance of noise (to meet worldwide standards!), performance and power delivery, all while offering a reduction in weight over your standard system.
What is an expansion chamber?
An expansion chamber is the 'header pipe' of a 2-stroke, which has a notably larger exhaust that comes straight out of the engine. Just like a 4-stroke, the shape, size and routing of an expansion chamber can offer increases in torque and horsepower, as well as a significant weight reduction over the standard unit.
Do I need to use a spark arrestor?
Spark arrestors usually come included with most 4-stroke mufflers, while they generally are not included with most 2-stroke silencers, unless it's an enduro or off-road specific model, such as the FMF Turbinecore 2.1 silencer.
Most motocross riders will remove the spark arrestor for closed-course riding and racing, while it's always best to keep the spark arrestor fitted if you're riding enduro and hitting trails through the bush, as it's designed to prevent any sparks exiting the muffler that could cause a possible fire.
A spark arrestor can also have an impact on the power delivery of your dirt bike, which is why some riders will either keep it in or remove it depending on their preference, plus it also reduces noise.
Do I need a full system, or can I just get a slip-on muffler?
To get the most of out your bike, we always recommend getting the full system for the perfect combination of increased torque and horsepower, however if the budget doesn't permit, a slip-on muffler or silencer will still give you great results over a standard OEM pipe.
Slip-on aftermarket exhausts will bolt straight onto your bike and OEM header pipe, making it an easy and affordable performance accessory.
Slip-on mufflers or silencers are made with an accompanying header pipe or expansion chamber of the same brand in mind, which is why having both will allow you to get the most out of a boost in power and reduction in weight (also, aftermarket header pipes just finish off that factory look with a slip-on muffler!).
What's the difference between a stainless steel and titanium exhaust?
Most exhaust manufacturers offer both stainless steel and titanium exhaust systems. A stainless steel system is generally more affordable, although it won't have the weight-reducing benefits of its more expensive titanium counterpart.
A lot of exhausts brands, such as Pro Circuit, Akrapovic and Yoshimura, will offer just one option in stainless steel, while there will multiple options in header pipes and mufflers in a titanium variant. FMF is one of the brands that offer its Megabomb and Powerbomb header pipes in both stainless steel and titanium options.
How to make a dirt bike exhaust quieter:
Noise is one of the biggest challenges the sport is facing at the moment, and that's why it's import to keep up your exhaust maintenance to ensure it's noise remains at a reasonable level. Now you might find that over time your exhaust is getting louder and louder, or maybe it's suddenly gotten louder.
There are three ways to reduce the noise your dirt bike produces, but the first thing you want to check is that there are no cracks or holes throughout the entire system. Crack, holes and damage can create a louder noise and reduction in power, so it's always best to inspect the system before going any further.
The most common way to reduce noise is to repack your muffler with new muffler packing. After time, your muffler packing can start to deteriorate and doesn't absorb or muffle noise like it once did - repacking your muffler or silencer will almost always help with making your dirt bike exhaust quieter.
The next thing is installing a spark arrestor - as we said earlier, most 4-stroke mufflers will come with a spark arrestor, which is simply installed inside the end cap. Installing a spark arrestor is an easy and affordable way of reducing noise. If you've done both of the tips above and your exhaust is still overly noisy, it's time for a fresh exhaust system.
How to make my dirt bike exhaust louder:
Most standard OEM exhaust systems are incredibly quiet (such as the Honda dual-exhaust system), which is why you might want something a little louder with a crispy note. The best way to achieve this is by installing an aftermarket slip-on muffler or full exhaust system. A muffler or silencer will make the most difference in the level and note a dirt bike makes, while an aftermarket header pipe or expansion chamber will make a more subtle difference in terms of noise.
How to clean a dirt bike exhaust system:
Cleaning an exhaust system is another super easy process that will go a long way in extending the life of your muffler and header pipe. You'll need a pressure washer, bike wash soap, a bucket and a general dishwashing scourer.
Remember to always plug your exhaust before starting the cleaning process, as any water that makes it down the muffler could find its way into the motor, causing serious damage.
You want to start by cleaning the bulk of the dirt off with a pressure cleaner, and if you keep up consistent cleaning, this all you have to do.
If you've let some dirt build up over time, or maybe you've had a mud race, you'll need to get your bucket of soapy water and your scourer, and start scrubbing the header and mid-pipe.
For the best results, it's best remove the system from the bike (if everything is dry!), but on some models, you might find that you can get to all the hard to reach places.
Once you've finished cleaning, remember to hit the header and mid-pipe with a multi-purpose spray to prevent any corrosion.
If you have any questions about muffler repacking or performance pipes don’t hesitate to contact the friendly team at MXstore
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