Update to earlier query on Dunstall Decibel Silencers

29 April 23

It seems none within this Norton crowd have ever gone internal on the Dunstall Decibel Silencers. So I ventured into the unknown and here are my results.
All this occurred today 29 April 23.

1 - I attached a carbide cutting bit to my die grinder with a 10" extension.
2 - I began to relieve the baffle from the can at approximately 7" below the inlet.
3 - The exhaust end had been cut free with the "Gatling Gun Nozzle" removed.
4 - Removed the blazed material around the flange that holds the baffle on the exhaust end.
5 - Once all had been ground away the baffle merely fell out.
6 - I was surprised at the absence of sound packing around the baffle. I can not confirm if it was ever there to begin with. I have owned this scooter since 1979 and have not changed the silencers that came original to the bike.
7 - The next step will be to clean everything up as it will be going to the chrome shop later this month or next.
8 - I will be fabricating new removable baffles and flanges so maintenance will hopefully not be a challenge in the future. ( May opt to blaze the new components back into place as before). I have not decided on this yet.
9 - Overall if my efforts bear fruit then I will have been able to maintain the original "Dunstall Pipes & Silencers" that came with the bike.
10 - I will attach photos of this adventure for all to see and comment upon if and when I figure out how to do it. (Just figured out the routine. Enjoy the photos.)
Anyway not bad for a Saturday.

Thanks


1 May 2023

The Dunstall Decibel Silencer Saga Continues and today's story is as follows:

After soaking the "silencer" parts in vinegar/salt solution I decided to get a little more aggressive with the cleaning. Rinsed everything in a water & baking soda bath to neutralize the acetic acid. Once all was dried I focused on the mounting bracket. Got out the "blue tip wrench" and heated up the bracket to help straighten out the dents and close up the mounting bolt(s) slot. There is a little more fine tuning to occur, but there is no point in getting "too froggy". I can detail the remaining imperfections with a file. Lastly I media blasted the baffle and as much of the interior of the can as I could. Overall it looks pretty good. Take a look at the attached photos as the progress in this project is moving on. I look forward to any comments and a big thanks to all who have viewed my earlier posts.

Yeah, they look about the same for the longer versions that have 3 nuts securing the baffle too. Pretty much straight through, no fiberglass packing. I have a set of earlier shorter like pictured and later removeable baffle. Both sound the same, great bark under acceleration.
I haven't used the shorter ones in 15 years, but bought them in 1973. Blew the transmission in 1974 and was back online with a 5 speed Quaife in 1975. Upon starting again, plenty of rust flew out of them! All the while, the 750 was in inside storage, so I was surprised at that. The later longer, removeable baffles are on the 850. One of the baffles cracked and split, so had to be welded. It seems the left cylinder exhaust suffers more vibration, as the silencer clamp also gave me issues with the 2 insert collars necessary for mounting on stock Commando exhaust pipes kept loosening and splitting apart. Welded them together and all good now.
I still weep about the set I bought on ebay from a motorcycle junkyard in Wisconsin who didn't read my email to remove Dunstalls from pipes, shipped in a flimsy cardboard box and arrived all dented. Sure, I returned for refund, but they were in great condition before lazy, inadequate packing. :-(

30 April 23

Thanks for looking at my post. Good to know about the packing. I am fabricating a cleaning tank this afternoon. I shall see if vinegar and a salt solution will clean silencer shown. It is a slow process from what I understand, but I have the time. Once again thanks for the interest.

I have a pair of '60s era Dunstall silencers which are sadly a little beyond use. One is 'ok' the other is rusted out. The baffles look a lot like yours:
They have a short angled section to the downpipe, and a second lug for a rear stay.
I've only seen them on Domis & Tritons, and have never seen any decent replicas for sale.

The ones badged as Dunstall Replicas available today look more like H**da silencers

If anyone knows of a source for these I'd be very interested!

This inspired me to review my inventory. I have two sets of Dunstall replicas that are pretty close to the longer silencers Dunstall sold mid 70's that are on my 850. One set is new the other slightly used. The new pair have fiberglass packing, however, very thin.

The second pic is what the packing looked like on the slightly used pair.
This is probably why some believe they sound better once they've "Broken In"

Based on the results of rapid deterioration, I will remove the new wrapping on the new set. They won't last anyway



.View attachment 106420

1 May 2023

The Dunstall Decibel Silencer Saga Continues and today's story is as follows:

After soaking the "silencer" parts in vinegar/salt solution I decided to get a little more aggressive with the cleaning. Rinsed everything in a water & baking soda bath to neutralize the acetic acid. Once all was dried I focused on the mounting bracket. Got out the "blue tip wrench" and heated up the bracket to help straighten out the dents and close up the mounting bolt(s) slot. There is a little more fine tuning to occur, but there is no point in getting "too froggy". I can detail the remaining imperfections with a file. Lastly I media blasted the baffle and as much of the interior of the can as I could. Overall it looks pretty good. Take a look at the attached photos as the progress in this project is moving on. I look forward to any comments and a big thanks to all who have viewed my earlier posts.

Deckard said:

This inspired me to review my inventory. I have two sets of Dunstall replicas that are pretty close to the longer silencers Dunstall sold mid 70's that are on my 850. One set is new the other slightly used. The new pair have fiberglass packing, however, very thin.

The second pic is what the packing looked like on the slightly used pair.
This is probably why some believe they sound better once they've "Broken In"

Based on the results of rapid deterioration, I will remove the new wrapping on the new set. They won't last anyway

Click to expand...

Well there you go !!! Nice to have this kind of input. Do you think that the wrap makes any significant difference?

Seawulf said:

Well there you go !!! Nice to have this kind of input. Do you think that the wrap makes any significant difference?

Click to expand...

I don't. Since it's pretty flimsy and doesn't last, it becomes what a Dunstall Silencer was anyway. Straight through with a metal baffle. I'd wager the Dunstall design was more efficient, but these replicas look pretty close.
My original installation literature from Dunstall said to richen up the main jet 2 steps, and I did. Always need to do a plug check to verify mixture.
I think it's pretty good information to anyone running these replicas, just open them up and throw away what's left of the meager fiberglass wrapping.

Sound is sound as it applies to an 850. You often know when things are not quiet right. As for the jetting - I ran across a guy named Greg Marsh. This fellow seems to be fairly knowledgeable about AMAL carbs. I will see if I can find his treatise on jetting. Very eye opening. Thanks for the dialog.

Yes, do go through your end to end tuning. Your air filter type and year of 850 may be factors in tuning. '73 and '75 differ from'74 carb manifolds and heads. If you're all stock components, not difficult, just optimize what you have.
You should probably update your profile so we know what year your Commando is.