5 replies to this topic

[smelling123]

Hi,
I keep hearing about having the exhaust packing done properly on the middle and back box - it is in fact mentioned in Don Morleys book, and how it can affect performance but I cant seem to find a definitive answer on what is correct.

So..can anyone confirm? Is it supposed to be very tightly packed or is looser packing better?
many thanks
Stu

[Canada280i]

I'll throw my response in here, although you should wait for other opinions as well.

I once re-packed my exhaust 4 times in the same day just to test the different qualities of each firmness of packing. The purpose of exhaust packing is to absorb sound waves and allow for expansion of exhaust gases exiting the cylinder. If you pack to tight the gases cannot expand enough and the sound cannot be absorbed into the packing. If you pack to loose the expanding gases will compact the packing within the confines of the silencer or mid-box eventually rendering it useless, and allowing it to move about. My experience has told me that the packing needs to be mid-way between too tight and too loose, I pack so that I can push my finger into it about half an inch, or pinch between my fingers but not enough so that my fingers touch. That way the exhaust gases have some room to expand in the chambers, but also the packing allows some movement to be able to absorb some of the sound waves while not being loose enough to be compressed away from the perforated tube the packing surrounds.

I would also be interested in any other opinions on re-packing, I think I have found what works best for me and my 315 but that may not be the case for everyone.

[smelling123]

Canada315, on 23 December 2011 - 02:29 PM, said:

I'll throw my response in here, although you should wait for other opinions as well.

I once re-packed my exhaust 4 times in the same day just to test the different qualities of each firmness of packing. The purpose of exhaust packing is to absorb sound waves and allow for expansion of exhaust gases exiting the cylinder. If you pack to tight the gases cannot expand enough and the sound cannot be absorbed into the packing. If you pack to loose the expanding gases will compact the packing within the confines of the silencer or mid-box eventually rendering it useless, and allowing it to move about. My experience has told me that the packing needs to be mid-way between too tight and too loose, I pack so that I can push my finger into it about half an inch, or pinch between my fingers but not enough so that my fingers touch. That way the exhaust gases have some room to expand in the chambers, but also the packing allows some movement to be able to absorb some of the sound waves while not being loose enough to be compressed away from the perforated tube the packing surrounds.

I would also be interested in any other opinions on re-packing, I think I have found what works best for me and my 315 but that may not be the case for everyone.

many thanks sounds good. Anyone else have an opinion on this?

[PSchrauber]

Just stumbeld here, as I had this question to myself just a couple of month ago too here my 0.02€ opinion:

I used insulation pads for the refill as the inner holetube of the mid section has an open end and I hade concenrs that loose rock wool as insulation might be blown away just because of the open end of the hole tube, here a sketch of the inside:



For replacing the insulation you have to cut the silencer body in two pieces, with a cutting blade of a small dremel, back side (red line in the sketch). Lift of the one half and take out the inner hole tube that is probably braced to the inner wall of the exhaust manifold. Clean the inside of the exhaust body and the holetube too, using a wire brush until the holes are free again.

Wrap the pad around the holetube. As the volume of the mid section is moduled you have to reshape the pad insulation with a sharp cutter to the form of the silencer plus you have to add some slices of insulation pads where the silencer have the bulge. To keep the long slices where they belong befor inserting the "package" back in the mid section body wrap some steel wool made for exhaust around. You need thick steel wool sepecial made for exhausts from a coil, the standard wool you get frm a DNY or hardwarestore will burn away.

Then it is easier to insert the package again. Look up that there are no voids left or that you have accidently pressed the pads too much. Then brace the holetube to the inner wall of the exhaust so the tube won't start to rattle. Now you can reweld the to piece together. I personal have no skills in welding or welding tools so I went to a car body shop that do restaurations these guys do a pretty good job.

I have no experience in long terms with this set up but had made some with my enduro bike, (KTM 500), where I have to replace the exhaust insulation regulary as the bike need a lot of two stroke oil and gas clogging up the silencer very quick. I therefor have modified the mid section of the exhaust so I can replace the insulation without cutting and welding, this is a huge advantage in terms of ease of servicing.



The rock wool insulaton in my experience only worked good when there where ready made inserts for the exhaust available, sadly they don't sell them anymore. The loose stuff don't work so well as also when right filled it will get blown to the rear end of the silencer in the long run, leaving a void in the beginning and a too much compressed area at the end. What I also noticed is that the loose rock wool does not absorb the oil so well. I now use glas fiber thread knitted wool that comes in plastic bags. The producer gives you the weight per liter volume that has to be used. You then calculate the volume of your silencer subtract the volume of the inner hole tube and then you have the weight of insulation wool you need.

This stuff works only if the holetube goes through the complete silencer body so no option for the Bultaco.

You just fill up the hollow between silencer body and hole tube if you have pressed to much you don't have enough material if you havent pressed to much you have exessive material left, in both terms you have to repeat the procedure until you have filled up the silencer just to the top. This material soaks also much better.

Here some links to the mentioned materials you can use for exhaust repacking:

steel wool, insulation pads and glas fiber wool: insulation material

hole tubes if you need a repalcement: hole tubes different sizes

spseial glas fiber wool for bikes with calculation of material you need, (in english): Silent Sport

[BOGWHEEL]

Have yesterday opened up a mid muffler, that i think has not been done since new. The perforated tube is wrapped in a single layer of wire insect screen size mesh.
Does this need to be replaced for any purpose please?

[PSchrauber]

As you have already opend the mid section.

The old mesh is the riminding part of the old insulation which kept your former rockwool insulation material which sat between the mesh and the holetube protecting it from beeing blown away. A new wrap with silencer insulation pads and then with silencer steel wool will reduce noise and might too improve performance.

If the holes of the holetube look clogged clean them so the holes have the full diameter, this will increase noise reduction, easiest way to clean the holetube is blasting.

Edited by PSchrauber, 09 January 2012 - 10:07 PM.