250 Monza: can it be made quieter?

[cooperplace]

the Silentium is a straight through design and the bike sounds like it. In the interests of maintaining good relations with the neighbors, does anyone have any suggestions for how it could be made a bit quieter?

[Sam]

If the end can come off use a length of stainless perforated tube wrap this lightly with stainless wire wool (using stainless prevents it from eroding due to condensation and the wire wool stops the pulses breaking up the fiber on the wadding) and then wrap with exhaust wadding.

[DewCatTea-Bob]

[quote= cooperplace ...
" the Silentium is a straight through design and
sounds like it.
does anyone have any suggestions for how it could be made a bit quieter? "

____ It may be that yours has had it's internal baffle removed, thus making it even more 'straight-through'.
__ The stock muffler normally has a single-piece baffle which screw-swirls the ex.air in one direction and-then the other (which baffles ex.air-flow more than the ex.noise),, and 'through' the center of the baffle, is a length of (about 30mm) tubing which is hollow & completely empty and-thus allows most of the ex.noise through. _ That tubing can be plugged-up with whatever you can find to stuff-it-up with (such as steel-screen rolled-up to stuff-fit* within), and that will rather simply reduce the ex.noise fairly well.
* Back in the past/old-days, others & myself would take-off the tip-end/cone-cap of the muffler-shell and-then knock-out the baffle,, and with the cone-cap replaced, it then sounded pretty-good, (unlike with the baffle !).
But when I earned a 'fix-it ticket' (for over-taxing my cop-luck within down-town streets), I reinstalled the stock baffle, but still worried that it wouldn't pass the inspection. _ So I filled-up the baffle's center-tube with a length of rolled window-screening. ...
The center-tube (I think) is a little over a foot long, so I cut-up a piece of aluminum-steel window-screen about 10-inches longer, and rolled it about a half-dozen layers thick and-then used some thin wire wound & tied around it to help keep it from soon unrolling whist getting inserted into the baffle-tube.
The reason for cutting a screen-piece so much longer than the tube's length, was so that once inserted all the way through, it could then stick-through and somewhat come-unraveled on the inside and thus-then become too large at it's inner-end to slide back-through (and possibly back out).
The finished job had about 5-inches of rolled screen sticking-out of the baffle-tube & flared-out at both of it's ends. _ And that screen-work partially blocking the ex.air-passage through the tube, combined with the flared-screening that sticks-out into the volume of the cone-cap, really helps to silence the ex.noise.
If you wish even more silencing, then cut a larger piece of screen and roll it even tighter (for additional layering) and make it another 5-inches longer so that it can stick-out further and-thus the flared-screen can then reach most all the way to the ex.outlet of the cone-cap.
It's a rather simple worthwhile job, (that you wouldn't want to do on a hot day like I recall having to do as a teenager) !
(BTW, the thought of using rolled-up window-screen was given to me by a BSA-rider who had done-same with his straight-pipes.)
____ Years later I've also tried much similar to that suggested by Sam, but with glass-packing material (after the baffle & inside the cone-cap's volume),, and that had a much nicer & quieter ex.sound, but the packing-material had to be replaced more often than I had ever expected would be called-for, (which was around every 200 ~ 400 miles, depending-upon packing-material quality).

____ Please let us know what you're thinking of trying-out first.


Hopeful-Cheers,
-Bob

[cooperplace]

Hi Bob,
thank you as always for your excellent advice. When the bike is back together (fork seals, rear wheel bearing, etc) I'll do as you suggest to keep the noise down.
Peter

[DewCatTea-Bob]

[quote= cooperplace ...
" When the bike is back together (fork seals, rear wheel bearing, etc) "

____ I suggest that you put-off the fork-seal work-job, or-else you may-not ride your Duke again any time in the nearer foreseeable-future.



" I'll do as you suggest to keep the noise down. "

____ Once you've thus-so reduced the exhaust-note volume-level, (as the screen-material transforms the sharp-barking NOISE aspect of the 'ex.note' into more of a rather puff-wizzing sound), you'll then more-so notice the working-noise from the engine itself. _ And to address that, you could obtain & install (at-least a dozen) of the little rubber-block insert-pieces that most-all air-cooled Jap.bike-engines have stuffed in-between the cyl.head-fins to help quell the cooling-fins from amplifying the internal working-noises.


Dukaddy_DUKEs,
-Bob

[cooperplace]

does anyone have any suggestions for how to get the tail piece off the muffler? it seems to be removable, but in 40 years it might not have been, and it's stuck on good and hard.

thanks

[DewCatTea-Bob]

[quote= cooperplace ...
" does anyone have any suggestions for how to get the tail piece off the muffler? it seems to be removable, "

____ The ex.cone-cap/tail-piece is indeed removable from the main muffler-body (after the ridge-clamp has been relaxed off-from it's clamping-position, [which I assume you must've already done]).
__ Have you already tried to twist it off (rather than merely trying to just pull it straight off) ?
Assuming so, then next you should probably try heating-up just the ex.cap and after it has gotten pretty-hot (while the main-body is kept from getting as hot), then place ice against just the end of the main-body, and then see if that process doesn't shock-loose the set-grip between the two pieces. _ If not, then you may have to try that process (or pretty-much the-like), several more times,, (and then use heat-gloves to grab the tail-cap, and/or rap the cone-piece from side-to-side with a rubber-mallet).
Although it could be possible to install some rolled-up screen rather from the inlet-end of the muffler-body, it'd be a more difficult job to get accomplished.
__ Please let us know if you make any gain-way.

____ Have you already found any screen-sheeting to use for the intended muffler-silencing job ? _ If so, can you tell what metal it's made of ?


Hopeful-Cheers,
-Bob