Ossa Mar Exhaust

[sivy]

Anyone had any experence decoking/repacking the exhaust on an Ossa mar 1976? mine appears to have had some work at some stage as both boxes have been cut all the way around and then welded back up. Is this the best way to do it? will the perforated tubes come out attached to one end only?

[woody]

The rear silencer isn't packed (assuming it is the small bullet shaped one) they have baffles, so nothing to repack in that. If it is the later, long tube type with exit holes underneath I've never done one so can't comment.

To repack the middle silencer is the stuff of nightmares as it is fiddley to say the least. The perforated tube is attached (welded) in at both ends so you can't just cut one end off and slide it out.

The way I did it was to cut open the body (just the cylindrical bit)lengthways by cutting two slots down each welded seam on either side. I then cut around the body at each end so that the body came away in 2 halves. Now, the silencer is is still in one piece except that the guts are exposed in the middle - looks a bit like a fish that has had the body eaten and the head and tail are still on.... (it's late and I was up very early...) Make sure that whatever you use to cut it open leaves a very narrow cut, otherwise the edges won't meet when you come to put it back together. I use the super thin cutting discs in an angle grinder. They leave a very thin and clean cut. I also found that they are extremely efficient at slicing through a human thumb knuckle down through the bone almost to the point of it being severed, so quickly that there is no pain and you won't even know you've done it until you see the blood on the floor and think to yourself - where did that come from? Another month off the bike. Anyway, I digress.

Now the fun bit. Whatever it was packed with originally has a length of wire wrapped around it several times. So in order to remove the old packing you will also have to cut away the wire and it can be a pain in the neck. Similar to removing wire you've run over from your back wheel. Once it is all removed you will probably have to clean out all the holes in the tube which will be blocked with carbon. How you proceed next depends on what packing you use. I use silent sport string/wool type so I replace one half of the body by tacking it back in place and then stuff it full of packing. I then tack the other half on but with a couple of tacks only so I can bend it open and shut like a flap/door. With the door open enough to get the packing in, I then stuff the remainder of the silencer with packing and then 'close the door' on it and tack it shut. Then weld it all up. Be careful as the metal is thin and easy to blow holes in it. If you are a competent welder and know what you are doing this won't be a problem. The fact that I'm telling you about it tells everyone else that I'm not a welder by trade and much swearing and screaming accompanied my efforts to weld it up without making it look like swiss cheese and playing chase the hole (steady...)with the MIG. How much packing you stuff it with is personal choice. I pack it reasonably tight but not crammed in to bursting otherwise it doesn't work as efficiently as it should.

If you use the wrap around sheets then you can wrap them around the perforated tube and then replace both halves at once and weld them back up.

Hope this helps. It definitely made a difference to my bikes when I did them, not only to noise levels but made them run much smoother at the bottom end of the revs again.