Tuesday, May 29, 2012

More Noise

One of the few complaints I've had, concerning my VTR250R, is the lack of exhaust "note". It is exceptionally quiet and I have a hard time hearing it even when I'm sitting at a stop light (disclaimer; in an effort to avoid further damage to my hearing, I used to race loud cars, I wear Hearos foam ear plugs). So, in an effort to increase the exhaust note without being obnoxious, I removed a portion of the end cap. A big thanks goes to the guys on forum boards. A few of them have already done this and it does not require any carburetor work (re-jetting, etc.). It's a 'simple' muffler modification.

Thanks to forum-mate John, here's a great image of what we're going to accomplish:

image courtesy of John Hilmer
The upper muffler is a stock unit. The lower muffler, which is actually attached to the exhaust system on John's bike, has been modified. If you look closely at the upper muffler, you'll see a distinct ridge (most noticeable at about 7 o'clock). That's a weld line and makes a perfect locator for the larger (2") hole saw.


  • A lot of torque is generated by the drill (I used a 1/2" drill but I think a 3/8" would work OK, too). It is not uncommon to have the bit catch and wrench the drill from your hand. Hold the drill securely.
  • The muffler is round which makes it hard to clamp in a vice or other securing device. So, leave the muffler on the bike, for now.
  • Most hole saws work best at lower RPM (200). You don't need to be at maximum RPM of the drill to get good results.
  • Be sure to use some cutting lubricant (drain oil, WD-40, Marvel Mystery Oil, etc.).

1/2" drill with stabilizing handle and 2" hole saw
The above image shows the set-up I used for the hole saws. I happen to have a auxiliary handle for my drill. In my previous experience with holes saws, I find it useful to have the extra handle. If you don't have one, be sure to maintain a firm grip on the drill and use a lower RPM. That way, if the bit does catch in the work, it won't wrench the drill from your hand. Do Not use the trigger lock (for obvious reasons).

Above, I've started cutting using that previously described welding ridge as a guide. I'm not using a pilot bit because there's nothing for the bit to drill into. Use some newspaper or cardboard to catch the metal chips (there will be a lot) and the cutting oil drips (the oil may run down the underside of the muffler and drip, to the ground, near the swing arm pivot. Make sure you have enough coverage). Note: wear hearing protection. The saw, cutting through the steel, makes a lot of noise.

Here, I've completed the cut. Notice the amount of metal chips on the muffler. There's at least twice as much on the ground and maybe three times as much inside the muffler.

Now, make the second cut. You have a choice here; 1 - you can use a 1.125" ( 1 1/8") hole saw which as an inner diameter of 1". The inner diameter, of the hole saw, is the same size as the outer diameter of the tube that protrudes from the end cap. However, the tube that's hidden behind the end cap has a diameter of 1.125" (1 1/8") which is the same size as the hole saw.

If you look closely, you can see the outer diameter, of the protruding tube, is shiny and has had some material removed. However, as you cut through the end cap, you cut right into the tube on the opposite side  of the end cap, resulting in this:

If you would prefer not to cut into that inner tube, you could go with choice 2 and select the next larger size hole saw; 1.250" (1 1/4"). This will allow you to cut through the end cap and not cut into the hidden tube. However, you will not have anything to help you center the hole saw. If you're of steady hand, you should be able get the cut started, albeit slowly, and get the results as shown in the first image (provided by John). Note the amount of metal chips generated by the cut. There's more hiding inside the muffler can.

Here's the (small) piece that we removed. To complete the job, you're going to need to remove the muffler (unless you don't mind shooting metal chips out the back of your bike - actually, given the small amount of air coming from the motor, there may not be enough pressure to do that). Unbolt the muffler from the hanger and loosen the clamp.

view from ground level
If your VTR is anything like mine, it's going to take some wiggling of the muffler to loosen it from the sealing gasket. The bike is going to want to roll backwards. Resist the urge to use your left foot as a chock. If the muffler suddenly comes loose, it's going to hit the inside of your left knee. And, that's going to hurt, bad (I did it twice so I know).

Here I have the muffler removed. The red arrow indicates the sealing gasket. Hopefully yours is in as good a condition. I used a little Scotch-Brite to remove the surface rust. If yours is shot, you may want to consider replacing it. I wouldn't be surprised if there's some asbestos in that gasket. Use caution when dealing with it.

Removing the metal debris, from within the muffler should be pretty simple. I just kept shaking the muffler until chips stopped falling out. However, due to the shape of the end cap, chips can get trapped. I have one of those small magnets on a (telescoping) handle. A few passes collected a lot of additional chips. I was surprised at how much more came out. I purchased a drum shaped grinding stone to help smooth the ragged edges from the hole saws. In retrospect, I should have purchased a cone shaped stone instead. I have a Roto-Zip tool and elected to buy the drum shaped stone from Dremel. However Vermont-American makes grinding stones that will work in a drill (they have a larger diameter arbor). V-A sells both drum and cone shaped stones. Again, choose the cone shape.

Results: Upon initial start up I was a little disappointed as the sound wasn't that much greater than the unmodified muffler. However, after the ride to work this morning, I'm pretty happy. The exhaust note can clearly be heard (over traffic and through my ear plugs). I seem to notice a "drone" right around 4500 RPM but it quickly dissipates above 5000 RPM. I also think I will try some muffler paint or BBQ grille paint before the exposed metal starts to rust.

Tools used:
  • 3/8" drive ratchet
  • 12mm socket
  • 12mm open/box end wrench
  • ball peen hammer
  • drift
  • 2" hole saw with arbor (Milwaukee brand)
  • 1 1/8" (alt. 1 1/4") hole saw with arbor (Milwaukee brand)
  • 1/2" drill with aux. handle
  • Grinding stone (cone shaped - Vermont-American)
  • Magnet on a telescoping handle

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