loud silencers 750 SF

Bert Reganze

Bert Reganze

Junior member
Location
Leiden NL
Bought a new set of exhausts DGM 5933 S for my 1972 750 SF on ebay. But they turn out to be much much louder than the old ones; they looked the same to me (old and new in picture). So 2 questions. Are there different grades of loudness available? And how can I make these ones more silent?
Hope there is a simple solution for this.
 

Attachments

  • IMG_0586 kopie.JPG
    IMG_0586 kopie.JPG
    291.6 KB · Views: 328
very early ones had a bolt on the rear bottom, which if you removed would allow the baffle to slide out, and could then be repacked, not that there was much of that going on!
CLEM
 
DGM 5933 S stamped exhausts with the slash cut at the end come in different qualities.
I have 2 sets, one heavier than the other and quieter.
Purchase origin unknown of both sets, but the heavier set is made of thicker steel, has better chrome and fits better.

HTH
Gerald


 
Thomas aus LAU said:
Please try to make a photo from back inside the pipes.

Original they where not really silent :-)

Thomas aus LAU
Click to expand...

Hi Thomas,

here are the pics, hope you have a solution. Even if they were not really silent originally, I want to reduce the sound.

kind regards Bert
 

Attachments

  • IMG_1267 kopie.JPG
    IMG_1267 kopie.JPG
    275.1 KB · Views: 242
  • IMG_1268 kopie.JPG
    IMG_1268 kopie.JPG
    209.9 KB · Views: 240
I already opened the silencers to see if there is enough packing material in it. It is completely filled with packing wool; no gram can be added anymore.
 
I lost the packing out of one once,when the screw dropped out and the baffle slipped back,made no difference in sound, they are what they are, ear plugs is all I can offer.or change the style.
 
Laverdalothar said:
You could make up some DB-eaters...
Click to expand...

I already searched for DB killers. But which one could fit to my 750? Or can I make DB killer myself. Where should they be placed. I wouldn't go for something which is visible
 
LJ-2 said:
I lost the packing out of one once,when the screw dropped out and the baffle slipped back,made no difference in sound, they are what they are, ear plugs is all I can offer.or change the style.
Click to expand...

And that is interesting information! So the exhaust wool does not work anyway. Unfortunately I sold my old silencers, so I cannot check what is inside these quiet ones.
 
if the internals of your silencer are original, what you should see inside is an inner skin, in the shape of a reverse cone megaphone, the outer is just a skin for styling, inside is the reverse cone with the packer after the cone. that may be why one pair is much heavier than another, the later SF1/2/3 system with the under gearbox lean angle limiter and the Conti type silenecers are very much quieter, , but beware pattern lean angle limiters are very often "empty" and they should not be.
CLEM
 
Could you please open the little screw at the end and pull out the inner part of the silencer.
Whith a photo we will see what we can do.

Do you have the connection between the two hoses near the cylinderhat?

30-40 years ago i had several times the job to reduce noise good sound when i had to go to the technical check (T?V) of my bikes.
It is possible to reduce the noise, but you will get an different sound.

Best Thomas aus LAU

 
CLEMTOG said:
if the internals of your silencer are original, what you should see inside is an inner skin, in the shape of a reverse cone megaphone, the outer is just a skin for styling, inside is the reverse cone with the packer after the cone. that may be why one pair is much heavier than another, the later SF1/2/3 system with the under gearbox lean angle limiter and the Conti type silenecers are very much quieter, , but beware pattern lean angle limiters are very often "empty" and they should not be.
CLEM
Click to expand...

The inner pipe is just straight and aligns with the exhaust pipes coming from the engine; it is completely perforated with holes from beginning to the end. There is no cone shape anywhere in the perforated part. In between the outer skin and the perforated pipe is the silencer wool. I will post some pictures of the inside in the future when the silencers are opened.
 
Thomas aus LAU said:
Could you please open the little screw at the end and pull out the inner part of the silencer.
Whith a photo we will see what we can do.

Do you have the connection between the two hoses near the cylinderhat?

30-40 years ago i had several times the job to reduce noise good sound when i had to go to the technical check (T?V) of my bikes.
It is possible to reduce the noise, but you will get an different sound.

Best Thomas aus LAU
Click to expand...

Hi Thomas,

WOW that is good news! I will pull out the inner part as soon as possible.

Yes, I have the balancer pipe just beneath the cylinder head
 

Attachments

  • IMG_0488 kopie.JPG
    IMG_0488 kopie.JPG
    92.8 KB · Views: 198
Yes, please post pics of the silencer internals. We can then look at some simple mods to slightly lower the sound levels. By your description, My silencers are like yours and I find them too loud. Unfortunately mine are welded shut so I cannot easily improve them.
 
When i got my first Laverda build 1972, it was relativ new. There was no wool inside the pipes.

In opposite to the SFC-pipes (see picture) the open "room" in the middle is missing and the drilled hose inside goes from the end till the first "wall/schott".
I will take the long endoscope-camera and will have a look inside.

IMG_6510.jpg


Best Thomas aus LAU
 
Bert Reganze said:
I already searched for DB killers. But which one could fit to my 750? Or can I make DB killer myself. Where should they be placed. I wouldn't go for something which is visible
Click to expand...

Hi Bert,

it is fairly easy if you are able to weld. A DB-eater is basically nothing else but an reflection type damper. Done right, it reduces noice without sacrifying power or torque.

Measure the inner tube diamter of the back-end of the muffler and  see if you can find one that fits. they come in differen diameters and are screwed in just like the damper-insert that you have already (but in this case, in addition to the damper insert!). See f.e.:

36mm:
https://www.amazon.de/dB-Killer-Universal-dB-Eater-Kr%C3%BCmmer-Auspuff/dp/B078K2TRXL/ref=asc_df_B078K2TRXL/?tag=googshopde-21&linkCode=df0&hvadid=345518677632&hvpos=&hvnetw=g&hvrand=16428713744983719567&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9044751&hvtargid=pla-751378586310&psc=1&th=1&psc=1&tag=&ref=&adgrpid=75266748688&hvpone=&hvptwo=&hvadid=345518677632&hvpos=&hvnetw=g&hvrand=16428713744983719567&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9044751&hvtargid=pla-751378586310


or

35mm:
https://www.amazon.de/MASO-Motorrad-Auspuff-Schalld%C3%A4mpfer-einf%C3%BCgen-k%C3%B6nnen/dp/B07QFPHQHB/ref=sr_1_8?__mk_de_DE=%C3%85M%C3%85%C5%BD%C3%95%C3%91&dchild=1&keywords=db+eater&qid=1595848531&s=automotive&sr=1-8

with the last one, you can see how they are build. If you can weld and drill the holes, you can produce one to fit your exhaust quite easily... ;)
 
Thomas aus LAU said:
When i got my first Laverda build 1972, it was relativ new. There was no wool inside the pipes.

In opposite to the SFC-pipes (see picture) the open "room" in the middle is missing and the drilled hose inside goes from the end till the first "wall/schott".
I will take the long endoscope-camera and will have a look inside.

IMG_6510.jpg


Best Thomas aus LAU
Click to expand...

The exhaust on Thomas's pic is a reflection type damper: most of the gas (comming from the headers) goes through the holes in the first part of the exhaust, have to pass the holes in the damper plate A, then through the ones in Damper plate 2 and then again through the holes in the last part of the damper, as the last tube is almost closed (or better: massively reduced in diameter) in the center chamber. For this type of damper, it is NOT recommended to fill the chambers with damping material, as this will reduce gas flow!

If the pipe goes completely through, than the holes in the inner tube are meant to send part of the noise to the chambers between the inner and the outer tube and they should/can be filled with damping material to reduce/absorbe parts of the noise. That is why they are called "absorbtion-type dampers".

This is an important difference of the construction of the two systems and shall not be mixed up, please!
 
You must log in or register to reply here.
Back
Top