repackaging dunstall decibel (early model)

[marp68]

When reading about repackaging silencers, some talk about using wire to hold the packaging material in place and some talks about using tejp which will burn up and let the material expand freely. Some also talk about not package too tight, which will actually not let the sound be dampened by the material but instead flow directly through the inner tube and out, and in the end sound higher.

What´s your opinion on this matter?

I have a pair of Dunstall copy mufflers, early model and possible to open, which sound a bit too high and sharp for my taste when revving the bike. I would like to lower both the volume and the frequency (more base like, if you understand my English). Like the Ducati Performance mufflers I had years ago on my Ducati Monster 900. A bit higher volume but still a nice soft low frequency.

I've also read that some people that have repackaged the Dunstall Decibel copy mufflers didn't noticed much of a difference.

Anyone out there with Dunstall Decibel copy mufflers

/martin

 

[jayel]

I have a pair of these...
http://www.jcwhitney.com/dunstall-style-megaphone-muffler/p2006467.jcwx?filterid=c14658r200j3
repacked them with stainless steel pot scrubbers (stainless steel wool) from walmart, stretched the pot scrubbers out held down with masking tape 4 to 6 each side lowers the tone quite nicely, use stainless as it will not rust or burnout like fiberglass packing

 

[marp68]

Yes, those the ones. Thanks for info.

You said yu used tape, which then burn up. In the link you also posted, one can see that they used steel wire to secure the package material.

What´s your opinion on not securing it, but doing it with tape and after burning up letting the material loose up inside the muffler?

Anyone knows what will be the difference regarding sound and performance using tape that burns up or wire that will not?

M

 

[5twins]

We used very thin wire (telephone wire) on our 2 stroke expansion chamber baffles years ago. Split a length of telephone wire down the side and pull out the individual strands. It held up well although the heat did melt the insulation off the wire, lol.

 

[marp68]

I repacked one of the mufflers with mineral wool mat. Rolled the inner tube with the matt. Used masking tape to hold it tight, so I could slide the inner tube back into the muffler. It lowered the volume very little and lowered the high frequency sound a bit.

Any suggestions to lower the sound more? Still to high.

I'm thinking that maybe the tape hasn't melted yet to let the wool spread out. I've heard that if it is packed to tight, the sound goes startight through instead of taking the way through the small holes in the walls and out into the wool. I'm thinking of using fishing line (nylon) instead of tape. Maybe it will melt more easy. Or I could let the end of it hang out from the muffler and then, after mounting it, cut it loose, so the wool can expand directly.

Any experiencies of fish line?

Jayel, did it lower the decibel much?
5twins, so the wool in your case didn't expand, but hold tight by the steel wire, right?

Martin

 

[Pipsqueak]

Hi Martin,

I am completely new to this so feel free to disregard my comments accordingly but I have a set of that well known and esteemed brand of Lu Hao silencers which were obviously fitted as a replacement as I cannot imagine Yamaha specifying them as standard. They are megaphones and were tinny and very loud so I repacked them with the usual fibre using simple galvanised wire wrapped around and tied off.

At first I packed them tight to the edge and then found the bike wouldn't start easily or run right so I removed half. Now that has taken the tinny edge off the sound while still sounding appropriately noisy. My Harley friends still call it the lawnmower though.

 

[marp68]

Thanks for input, Pipsqueak

One of the problem is, I think, that the diameter of inner metal tube with many small holes is to big. So it will sound high no matter how much wool I wrap around the inner tube.

I've read about people that put metal things through the inner tube to, so to speak, force the sound to take other ways than more or less straight through. Since some mufflers are even built this way.

So now, for the other muffler, I'm thinking of put thin bolts, nails or similar through the inner tube to see if it makes a difference. I will also try using more wool at the upper and broader part of the mufflers.

 

[Pipsqueak]

I maybe venturing beyond my knowledge here but inserting sharp metal objects into a tube that has a lot of air blowing through it may have safety implications. It would certainly disrupt the airflow which may help your cause or may hinder by generating new problems.

Mikesxs sells a replacement baffle that may help or simply changing the silencers may prove better in the long run than all the fiddling around. We are lucky in that replacements for universal silencers are cheap. One of my Harley friends paid $699 for a set of Vance Hines pipes. They sound and look great of course but I can't follow him closely on a ride or I get a headache.

Good luck

 

[marp68]

True, to much will stop the airflow. These inner tube have a diameter of 5 cm. And the small holes are 5mm.

Any link to an example of one of those replacement baffle?

 

[ReycleBill]

While I've no experience with Dunstall mufflers, here are some generalizations that might help.

Think of pipes like musical instruments. Longer pipes and mufflers will lower the frequency of the sound. Or creating a longer path within the muffler. Shorter pipes, shorter mufflers and shorter paths raise the frequency.

Smaller holes will raise the frequency, larger holes will lower the frequency.

As for packing, I've found brass wool will last longer that so called, "stainless steel" pads. Most of what is sold for stainless steel these days has a very low Nickle content and will soon rust.

 

[Tomterrific]

Knock out the plate inside the perforated tube or drill biger holes through it. This makes the muffler louder but deeper in tone and the packing doesn't blow out as fast.

As you put the baffle back into the muffler case there is a small gap right before the baffle is bolted. Use this gap to insert small tufts torn from the glass or steel wool with a screwdriver, popsicle stick or other poker. It takes a little time but lots more damping media can be inserted which will quiet the highs and make the sound 'rounder'.

 

[marp68]

Thanks, tomterrific

Exactly what "plate inside the perforated tube" do you mean? See image. Don't think I will drill bigger holes though, it's way to loud already and I don't want to destroy something that can't be changed back.

I think I will try your suggestion about inserting small tufts through the gap. I will also try to wrap more wool carpet around the rear part of the tube before inserting it, since there is more space for it to expand there.

I haven't looked at the first baffler yet, so I don't know if the tape has melted yet. Also a bit hard to do after mounting it... used pretty much tape to wrap it tight making it easier to insert.

So I'm thinking of using fish line (nylon) this time to tight and secure the wool aorund the tube, and then lock the end part of the thread to the part outside the mounting plate. Then I can just cut the thread, the thread will be loose inside which will let the wool to expand easier inside.

 

[marp68]

Here's an image of a double solution. First a wrap with steel wool, secured with steel thread, and then a fiberglass mat wrap, secured with tape that will burn away eventually.

Maybe the extra steel wool tightly secured with steel thread could lower the volume extra...

SORRY! Steel wool doesn't seem like a good idea... Read this on another forum...

"I ended up using steel wool and wrapped the core up fairly snug. I had enough layers that it was a good fit. Well less then 50 miles and the bike sounded like a tractor. When I took it apart nearly 1/2 of the steel wool was burnt to a dust and the rest wasn't far behind. It also created terrible heat on my pipe"

 

[Pipsqueak]

My suggestion, Martin, would simply be to try the glass mat, wrap firmly, and tie off with wire.

As I said before when I wrapped it thickly around the baffle it all bunched up at the end of the pipe and restricted it so much the bike didn't want to start or run properly. I used wire for that reason in that with tape it would have burned off and then I would have a pipe with a tight wad of mat at the rear of the pipe. I ended up wrapping about half way the diameter of the pipe and all ran well.

You can only try different versions and then adjust it later if you don't get the results you want.

 

[marp68]

I repacked the other pipe last night. I did the same, since it was impossible to add more wool after inserting the tube with mat wrapped around it. Since I used tape on the other pipe, I used it for this one as well. So the flow resistence would be the same over time.

I will run this for a while, and maybe next year try with steel wire if I'm not happy enough with the results. After the tape has burnt off I think I will check whether or not the wrapping has slided to the rear. Hmmm, how does one check this, since the wool slides towards the rear when removing the tube....

Thanks everyone for input.

Getting colder here in Sweden now.

Cheers

M

 

[marp68]

Okej, so I went for a ride this weekend... Nice weather but cold...

I'm really dissapointed though. The only difference i notice, is when idling. Only then it's a bit lower in frequency which also cause it to seem lower in volume. But driving, it's like an airplane... Okej, a bit cool, but annoying and disturbing in the long run...

So what to do? Even if I could a stuff a liiiittle more wool in, it wouldn't be enough. So the only other solution would be to put something inside the inne tube. Not to much though. But removing the inner tube again, I would have to buy more wool mat and repack the the silencer as well. And would it help...? Lot of job for maybe nothing...

The other solution would be to buy new silencers, maybe second hand. Anyone know about silencers that look okej and has a lower volume and frequency sound, more like original?

M

 

[ReycleBill]

Perhaps lollipops in the pipes ahead of the muffler? They are infinitely adjustable.

 

[marp68]

First time I hear about them. Smart thing!

But shouldn't they be mounted at the end of open pipes. The inner tube on the Dunstall is closed at the end and has a welded wall inside at about midway.

See images in previous post

Suggestions, please. Seems like a really clever idea.

 

[ReycleBill]

First time I hear about them. Smart thing!

But shouldn't they be mounted at the end of open pipes. The inner tube on the Dunstall is closed at the end and has a welded wall inside at about midway.

See images in previous post

Suggestions, please. Seems like a really clever idea.

They were designed for and most often used in open pipes but I see no reason why the couldn't be used ahead of mufflers as long as they don't get in the way of mounting your muffler.

Another way might be to build a crossover just ahead of the mufflers. A crossover would lower tone and make more low end torque without reducing top end power.

 

[marp68]

Seems like good things to start with!

Do you mean in front/outside of the "five gun" end part, when you talk about the crossover or the lollipop?

How would the crossover look like, you mean? Could you perhaps draw a scetch and post it?