Tom's BMW R850R Muffler, Part Two
This is the inside of a BMW muffler. The pipe in the center is the outlet, which has rusted through, making the motorcycle loud. There's no packing inside, just a baffle.
The inner components are normal steel, not stainless. At the very end of the outlet pipe, the pipe rusted through, and my muffler got quite loud. This muffler has been on the bike nearly 10 years, and I think the bike was stored outside some of that time.
This was a difficult and time consuming repair. I probably would not recommend this repair. I hope this page is interesting to anyone wondering what is inside a somewhat older BMW motorcycle muffler. I don't know how much I've extended the life of the muffler. A new muffler is close to $1000, and that's a lot of money to me. If the muffler were more affordable, I would never have done this repair.
The metal cutting and welding makes a big mess in the garage. My end result is solid, but not very pretty. The muffler is much quieter after my repair, and since I extended the outlet pipe, and pointed the pipe down, the exhaust isn't hitting the bottom of my side case. The BMW left case has a small section of fiberglass mat attached to the bottom to deal with heat from the stock exhaust. Even with my repair/modification there will be a lot of heat under the case.
Note that the BMW muffler is a double wall construction, with a layer of insulation. My repair is single wall. If the cases were off, and the muffler was hot, it would be important to keep people (i.e. a passenger) away from the muffler. However, I've always got the cases on, and the front of the exhaust where it exits the cylinder heads is much hotter.
I'm surprised that BMW didn't make the outlet longer. Doing it to BMW standards would require a heat shield or double wall construction, but that's not too tricky. Also, this is a very expensive part. I'm surprised that the inner wall and pipes aren't stainless. If this muffler were 100% stainless construction, I'd never have had a problem.
