Low budget performance silencer with spark arrester

[Smacaroni]

I've been saying I was going to post a DIY silencer for minis, specifically the PW80 for about two months now. I just didn't get time to do it. So, here it is.

***********The following information is provided free for personal use. Any commercial use, you must contact the author. Commercial use means you intend to make money, regardless of how, why or for whom.

Working with power tools and welding is dangerous. Take proper precautions.

This information is provided without warranty.**********

This method should work for just about any bike. As a matter of inside diameter, you want this to be 1/3 to 1/2 the size of your silencer housing's diameter, but no smaller than the diameter of the "in" side of the silencer.

You will need to purchase a few items from the hardware store and possibly muffler packing from a motorcycle shop. I assume you have a few odd pieces, like sheet metal screws and some scrap sheet metal of some type, kicking around your garage.

Purchase gutter guard (stuff to keep leaves out) and three washers which are approximately the inside diameter of the silencer. In the case of the PW80, it's 1.875" so 1 1/2 is too small and 2" is too big, but buy the 2" fender washers and I'll show you how to make them smaller using basic tools. The cost of a 5 pack was $10 and washers were $0.24 each. Make sure both are steel.

You can cheap out on muffler packing by using the blue air filter screens from your forced air home heater/air conditioner. The good news if you go that route, you can use an old one, it won't make a difference.

So your total cost if you buy muffler packing is around $18.

You'll also need a piece of metal window screen about 2" by 2" (or what ever size washer you use), and a piece of pipe that's about the diameter of your inner silencer diameter (if you don't have any, buy a 2" long piece of black pipe from the plumbing section - $1) and some (2 or three) metal screws, bolts, rivets or any other type of metal fastener (not pictured). Optionally, you may use a small strip of sheet metal, in this case, I used some left over 2 1/4" exhaust tube about 1/2" long.

First, remove the existing silencer core. If you have one. These seem to be one of the first things wanna be tuners toss without regard to what it actually does. Or they go hacking on it which may or may not do anything good. We won't destroy it, so you can always put it back in later.

Measure the inside diameter as well as the depth. Be mindful that some silencers (including the PW80) has multiple chambers. The rear most chamber has a smaller ID than the rest of the body. We'll actually use this to our advantage, but if you really want to, you can remove that using any means you see fit. You'll get a slight gain in performance doing this, but it will be a lot more work.

Now that you know the depth, cut a piece of the gutter guard to length, I would go at least 1/4" over. It's easier to cut off than put on.

Use the random piece of pipe (I used an old clip-on bar from a wrecked bike I bought) to form it into a tube. This stuff is really easy to work by hand, no tools are needed. Cut it so there's one diamond shaped level over lap.

Get your washers, stack them and drill two holes towards the outside of the washer, this will serve to keep them aligned during our next few steps. Once the holes are drilled, use wood screws or drywall screws to mount them to a piece of scrap wood. It doesn't look like it, but this is actually three washers stacked and attached to the scrap wood.

Now, use a hole saw to cut the inner diameter to match your random piece of pipe. If your washer is too big to fit directly inside the silencer body, use another hole saw to cut that smaller. My experience has been a 2" hole saw will cut an inside "plug" at around 1 3/4", which happens to be really close to what we need in this case. I highly recommend using a drill press during this stage since it is easier to keep everything centered if you clamp this to the drill press base. However, I did another one using a hand drill and it turned out OK. One thing to note, regular wood, like a 2X4 is a better choice than what I used.

After cutting both these holes, the pieces are extremely hot! You can probably see in the photo that the wood actually started smoldering.

[Smacaroni]

After it's cooled down, place the metal window screen piece between two washers and screw them together.

Trim screen. This is a rudimentary spark arrester.

Now, cut three sections off your random piece of pipe about 1/2 to 3/4" long, weld one to each side of the spark arrester and one onto the remaining washer.

As you can see in the photo, I was having a bad welding day, a very bad welding day.

While you're at it, tack weld your mesh tube onto the single washer.

Check for fitment. Worry more about length than snug fit between the silencer body and your insert at this point.

Wrap the sheet metal into a circle and insert this into the end of the silencer body, make sure it fits pretty tight and will be able to accept a tapped bolt (PW80 is 6X1.0 mm) hole to keep this all in place. You can alternately use an ordinary nut to keep the silencer guts in the body. If you do that, I would recommend drilling a hole on both top and bottom of the silencer body.

Once you're satisfied with the fit, weld the mesh tube onto the spark arrester end.

If you're using the sheet metal to cap/seal the end, you'll want to weld that on as well.

At this point, I finally decided find out what was going on with my welder. It would feed really fast and then really uneven and then jam. I'd unjam it by pulling the wire out from the gun and it would act the same way again. As it turns out, the wire spool unspooled and made a huge mess inside the case. So after fixing that, you'll see that I was now only having a sub-par welding day.

So clean up the welds and check fitment one more time:

While you have it in there, drill the hole for the bolt and tap it. If you were having a bad day with the welder like I was rendering the screws decorative, now is a good time to cut/grind them off. If you want to replace that screen later, you can just drill them out and use rivets.

Now, paint the tip with exhaust or header paint. While this isn't going to see as much heat as the other end of the exhaust, it's still going to get mighty warm.

After the paint has dried, pack it. I like using masking or in this case painter's tape to hold it all in.:

Stuff it in the silencer body, insert the bolt and you're good:

For comparison purposes, the stocker vs. the DIY performance muffler:

So what does it sound like?

You may notice that the bike is smoking excessively. This is unrelated to the silencer. We adjusted the oil pump output and the gas tank still had 32:1 pre-mix in it, so with the oil pump connected the bike is running about 10:1 oil ratio during this video. PW80s will run on damn near anything.

Special thanks to Super Hunky for the household air filter as muffler packing tip.

[Smacaroni]

For lack of a better place to do it, I'm posting a photo of the stock guts for someone who asked for a picture.

[CarterKraft]

Thanks allot, that will really help me out.

[CarterKraft]

Is the exhaust outlet through the pipe right after the turbine? Like the tube is sliced 180°.

[Smacaroni]

No. The exit is through the round end. The cone and turbine are deep in the silencer, then there's a cross-shaped section that ties the "bullet" as some people call it to the pipe that leads to the end. I presume the second cone has some sound deadening qualities. Which as you've noticed, the bike is quite loud without it. Doesn't make any more power, but it's much louder.

[CarterKraft]

Sorry for wearing you out on this. See my pic to clarify the exhaust flow. It comes in towards the point of the "bullet" gets swirled by the fins and then the airflow goes through the tube or does it have to turn 180* and go behind the funnel piece and into the rear pipe.

 

[Smacaroni]

A, all the way. B is just there, I presume, for noise cancelling.

 

And it's no trouble at all. Some people consider me an expert on this bike. I like to think of myself as a guy with perhaps a little too much free time on my hands, at one point in my life. Not today though. It's nearly 7:00 and I still haven't eaten dinner yet, on the company dime no less.

[CarterKraft]

I am one of those. I have followed many of your threads over the years and just recently lucked onto this bike like I said. I forgot all about them really. My daughter had a pw 50 up until a few months ago but i sold it as she was just too big for it.

This deal came along and I'm glad it did as it will be perfect for her for a long time.

I'll post some pix of what I come up with.

Thanks for your info.

[90atk]

is there suposed to be muffler packing in a stock muffler? i just took mine apart and there isnt any in there.

[Smacaroni]

The stock PW80 muffler has no packing. It's purely a what do they call it, resonance and cancelling muffler to reduce noise levels.