fitting aftermarket mufflers

[gray am I]

To get historic registration on my 78 special I have to remove the cool sounding shorties and fit aftermarket 24"megaphones, when I removed the existing mufflers I found a bit of a mess, the origonal double walled pipes had been cut off and the inner was welded to the outer, I dont think I will be able to trim and clean the pipes to get an internal sleeve and get coverage over the old drain holes, any ideas? how to tidy this up. Also the megaphones I picked up at a swap meet run a 1" tube up the middle of the muffler, gasses exit into the body back into the tube and out through a perforated tube, will these be ok or will they be too restrictive

 

[fredintoon]

Hi gray,
ooh, that's ugly up there.
Don't worry about the outer tube drain holes, the outer tube is only there to look good.
I'd clean up inside the inner exhaust pipe with a die grinder until it was nice and round and then shove a muffler adapter piece inside it. One end fits inside the pipe, the other end fits inside the aftermarket 24" megaphone.
Someone posted a photo a while back of how it's done.
And don't worry how the meggas sound, neither. You can swap back after the traffic nazis have signed off on it.

 

[XSLeo]

With the inner welded to the outer, I would do part of what fredintoon suggested. clean up the weld so it flows better. The weld seals the two pipes together.
This lets you just slip on most any muffler. You may have to use an adapter, most mufflers come with a set. Short steel sections of pipe that fit over the head pipe to enlarge it so the muffler has a snug fit. Once clamped down the muffler seals to the outer pipe, with it sealed to the inner pipe with the weld the exhaust has to go out the muffler.
The earlier exhaust of the standards used a slip on muffler The head pipe was done very similar. The inner pipe was expanded to touch the outer pipe. Then they compressed the outer pipe to give a bit of taper and seal the two pipes together.
Leo

 

[nj1639]

The Special headers that I've dealt with have a frame mounting tab or ear located just a bit further to the front of that mess in the pic.......not sure of the early '78 though.
If the tab is there, I'd cut through the header just aft of that tab, get the adapter and a clean start.

 

[gray am I]

thanks guys! shoved a rag up the pipe and ran a die grinder around to get rid of the weld dags now just waiting for sleeves to fit my mufflers, still not to sure about the internal baffles i'm hopeing that they won't be too small.