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

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.

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?

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

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?

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 January 9, 201214 yr by PSchrauber

More very helpful advice thankyou:  reading up before tackling my 191 exhaust system.

jj

this btw is the top tuning tip on sherpas. You can actually hear one that is "tinny" its a distinictive sound which means it needs the repacking. Mid box more important than back box.

And when they need repacking, as well as sounding awful they don't run very well at low revs

Thank you for the advice. On the to do list.

There is a rear section on sale locally, so may procure if affordable, and keep on the look out for front section for my 191.

Frame is in for straightening and aligning: top tube bent in 2 planes, swinging arm out of alignment, and forks may also be out. Hope to get it back by end of the week.

And seized bonded type swinging arm bushes mean they need changing. The rear engine mounting is "floppy" as not been clamped by bushes, and is worn on engine mounting ears. Needs welding and machining to sort properly. 

jj

16 hours ago, jonjeans said:

Frame is in for straightening and aligning: top tube bent in 2 planes, swinging arm out of alignment, and forks may also be out. Hope to get it back by end of the week.

 

jj

WHOA THERE, if its the frame bent down id sort it if bent up it shortens the steering a bit.

 

Edited January 23, 20188 yr by nigel dabster

18 hours ago, jonjeans said:

 

The rear engine mounting is "floppy" as not been clamped by bushes, and is worn on engine mounting ears. Needs welding and machining to sort properly. 

 

This type of alloy mounting was not one of Bultaco's more successful designs........

Makes good sense to replace it with a steel  fabricated item, as fitted to the later bikes. (like the white one in this pic.)

Also, when you refit the engine to the frame, pay particular attention to the condition and fit of the head steady .

Edited January 23, 20188 yr by lorenzo
further info.

Many thanks for advice. I have seen the steel ones for sale at InMotion. Will do that with swinging arm bushes upgrade.

jj