Re-Skinning 4106 Muffler

[OneLapper]

Okay, this is not for the weak of heart.  This is for the people out there that have trouble (morally or monetarily) spending over $1200 on muffler when they didn't spend much more for the entire bus.  This for the down-troden....  I digress.

This is the first installment of my muffler project.  Please bear with me as I learn to resize and post pictures.

Now a little background.  I have a 1964 PD4106 conversion that hadn't seen much in the way of real maintenace in the last 10 or so years.  I knew it needed tires.  I was told it had new brakes (that's another story all together).  The radiator popped a hole 125 miles after I bought it (had it recored for $1500).  She  starts and runs, my daughter loves going for rides and my wife thinks I'm out of my mind.  I think it'll be tons of fun to drive around with the family and friends, spend some weekends here and there, with the ultimate goal of taking the summer off and driving it around the country.  Hey, ya gotta have goals, right?

Back to the muffler.  It appears to have already been re-skinned, unless the old GM mufflers came with two layers of metal on them.  I'll let the experienced busnuts be the judge.

Pictured below are the tools I used and the guilty muffler.

[OneLapper]

I started by cutting a ring of metal from around the bottom part of the muffler.  I was able to "see" inside the muffler which made it easy to see where the skin was weld to the internals.

You can clearly see the two layers of sheet metal.  The sheet metal cut and peeled away from the rest of the muffler easily.

[OneLapper]

Is anyone surprised that this muffler has a 6.25" inlet and a 3.5" outlet?  I plan on opening out the outlet, but more on that later.  As you can see, the internals of the muffler are in good condition, and it appears that the muffler rotted from the outside in.  It was also apparent that exhaust condensation pooled in the bottom of the muffler.  This must have happened when the engine was started but wasn't run for any length of time or under any load.

[OneLapper]

The further up the muffler I worked, the thicker the metal became and the better the overall condition appeared.  That gave me the thought that maybe I didn't need to remove all of the sheet metal, saving me some time and hassle.  I haven't decided how far up I'm going to cut.

Here are some more pictures of the inside of the muffler.

I'm going to have to finish this post at a later point.  I won't be able to get back to the shop until this Saturday.  I'm off to pick up a power steering system tomorrow.

Please feel free to offer any advice or direction to go with this project.  My plan is to attempt to enlarge the outlet of the muffler to improve the flow and reduce some of the back pressure, as well as weld a new outer layer of heavy sheet metal to repair the huge hole.

[TomC]

Muffler companies makes same side in and out mufflers with 5" in and 5" out that would open up that stuffed up 3.5" exhaust.  Wouldn't that be easier?  Good Luck, TomC

[TomC]

I realize that maybe you want to do this project for the challenge of it.  But, me, I would just buy a new one.  While they don't make a direct replacement, there are others that could be used.  For example, I went online to Donalson and found this muffler- M120750.  5" inlet and outlet on same side, 12" diameter, 26" long with 31.63" overal length, 12-18 dba reduction (might not be quiet enough).  And they have many more.  Just an idea.  Good Luck, TomC

[OneLapper]

Hi TomC

I'll check out the Donaldson muffler, that's for certain.  I had looked online and went to the truck parts store and looked at their muffler books, but didn't come up with anything that would fit within the space.  I'm willing to get creative.  Thanks for the input.

Mark

[Mrbill4108]

Are thinking of just making the muffler shorter using the metal that's still good?   I've seen a 4106 that had a muffler that was about half as tall as a stock one and the owner mentioned that he didn't believe that is was any louder then the stock muffler.   I didn't have time to stay and hear it run.  The shorter muffler sure made the engine compartment cleaner looking.  Also with a shorter muffler you'd have better access to the side and back of the engine.

Mrbill4108 

[OneLapper]

From what I can tell the parts manual shows that there was a 38" tall muffler and a 28" muffler, each have a different part number.  My muffler is the 28" version.  I have seen pictures of the taller muffler on this board (somewhere).  I have no idea what the difference would be in them.  I don't think it would have much to do with noise and certainly not performance.  The most restrictive part of the entire exhaust system is the 3.5" muffler outlet. 

I understand that the DD 8V71 engine like open, free flowing exhaust systems.  After making a couple phone calls to some smart friends, we came to the conclusion that this engine flows approx 780 cfm at 2100.   A 5" inlet with 5" outlet will literally have twice the cfm capacity that this engine will need at full throttle, so a smaller 4" inlet/outlet muffler will be a close match in regards to cfm.  I haven't decided which direction to go:  New 4" muffler, new 5" muffler, or modify & reskin original muffler.

I'll have some time tomorrow to work on it.


Mark

[pvcces]

OneLapper, there are a couple of things to think about.

Increased backpressure reduces scavenging, something that is at the heart of this two cycle process.

Increased back pressure INCREASES the pressure of the air charge, which may help at moderate elevations.

I think the factory sized the blower to the application.

For what it's worth.

Tom Caffrey
Suncatcher
Ketchikan, Alaska

[Burgermeister]

Why not consider replacing the outside skin with Stainless?    Drill a small weep hole in the bottom to allow the condensation to purge.