Topic: Original Honda Muffler question for 78 CB750K

[cookindaddy]

I have a set of these pipes (HM405) that I have not yet mounted on my bike. I'm looking forward to replacing my current 4 into 1 with these.

All of them look pretty good on the outside. There are no through holes and the chrome is cleaning up very nicely.

My question has to do with the one pipe which is on the left in the picture. It is missing the inner tube. The picture shows about what I can see up the pipe. The hole seems to be mostly clear although the damping material (is it Fiberglas) seems to be collapsing into the area where the tube used to be. I haven't tried to blow air through it yet but wanted your advice about how to deal with this pipe?

Should I just mount it the way it is and hope that the pipe is clear and the damping material won't collapse further, blocking the exhaust gas path?

Should I attempt to clear out the passage and if so, how?

Should I make up a substitute tube and weld it in place to the pipe? I think the one I saw coming loose from another pipe was a tube with holes drilled or punched all the way along it. Any ideas about what it should be and how long it should be?

Any other thoughts would be appreciated. They are a very nice set of pipes and I know they are rare and unavailable from Honda. I don't want to blow it.

Thanks

[cookindaddy]

Has anybody ever cut one of these apart? What does it look like inside? Does the main pipe continue thru the center of the muffler or does the exhaust gas feed from the outside of the damping into the center tube at the outlet? (Hard to describe what I'm meaning, but hopefully I'm making sense)

[ColinMc]

You going for stock looks but better sound? I wonder how they'd sound with all the baffles yanked out and the fiberglass removed...lol

Sorry no help from me...someone must have experienced the same thing. I thought the baffles could be replaced on these though?

[cookindaddy]

Thanks.

I'd love to know how.

Anyone?

[GammaFlat]

I don't know but I have the same situation.  It'd be great if they were like the HM341's or HM300's with removable baffles.  If anyone's ever repaired these, I'd like to know how.  My best guess would be to cut baffle out, repair and weld back in place 

[cookindaddy]

I'd like to find a crummy, unusable one and cut it lengthwise to see how it is made. Perhaps that would give some clues?

[GammaFlat]

As I look at your picture, it makes me wonder if the center portion is pressed or screwed in... it must be - probably pressed.  If that comes out, it can be repaired.  The arrows point to an irregularity in the "ring" that I have verified with my pipes.  They all seem to have this, so maybe it was used to rotate the piece in at the the time of manufacture. Maybe I'll grab onto my bad pipe's baffle and give it a tug?!

[Toxic]

Seems like a few of us with the same problem.
My 77 pipes had the same issue.  The center portion may be pressed in but on mine there was no way I was able to separate them.
I drilled out the entire endcap so it was about 2 1/4 in dia.  Then I was able to remove the end baffle. It is not a straight through design the exhaust gases look to follow a series of chambers.
Basically mine has the last 8 or 10 inches removed of any baffles.  I know it will change the sound but I don't know by how much.

With the entire inner end cap removed or the area inside of where you see the 1/8" hole, I was able to have a 2 1/4" industrial washer welded in place.  This finished the end off nicely.

Holler if you want a pic of what it looks like.

[GammaFlat]

Wow - I'd love to see the inside.  I'd also like to see what you did with the end. 

John

[Toxic]

final pipe... might be a press fit but I couldn't separate them



inside





pile of I don't know what that came out of one of the pipes



easier to do the cutting with the pipes on the bike

[Toxic]

final result



The flash makes the welds look worse than they really are.

I was going to make my own baffle and have it welded onto the backside of the washer but I decided against it.
It would be easy to do.

[GammaFlat]

I'm anxious to hear what you think of the sound.  Maybe an audio file when you get it going. 

[Toxic]

I'm anxious to hear what you think of the sound.  Maybe an audio file when you get it going. 

Me too... but it will be couple of months.

I'm getting to the point where I have enough done to start a build thread.
Hopefully in the spring it will be running.