The original cast iron silencer was missing from my engine when I got it so I decided to make my own "reasonable facsimile".

Apart from a Chinese lathe and a drill press I have no other metalworking machine tools so this had to be made using available tools. These included an angle grinder, hacksaw, welding machine and a homemade disk linisher. All parts used came from scrapyards with the exception of the bolts and gaskets.

The hardest part was finding domes of the correct size but I eventually found a small gas bottle at a scrapyard that had 114mm O.D. domes (12.7 mm smaller) and decided to use this. I also had an old rusty piece of pipe which fitted perfectly to these ends.

Using the diagram from the parts manual of this engine, a drawing from Peter Lowe in Australia and a silencer from a friends 3 H.P. engine I redrew the silencer on my CAD programme but now using the avilable parts. I never managed to establish the correct diameter for the 6 H.P. silencer but after some research decided that it was probably about 5" (127 mm) diameter. I changed the baffle pipe from a single (loose fitting) pipe in the original design and rather used 2 pipes which met in the middle with the top one being removeable (see sketch). I can remove the top baffle pipe (just for fun) if I want a bit more noise but the engine does have a lovely sound with the baffle in place.

The gas bottle was cut with an angle grinder, leaving a small part of the inner pipe in place (this would help in locating the new "body"). I machined a hole in each dome for the inlet and outlet pipes.

    The next part was to be the most difficult. This was making the flanges for the top of the silencer. These are not just the normal diamond shaped flanges one normally sees but have a concave shape near the bolt holes. (I know that it would have been very easy to just have these laser cut but that would not have been as much fun).

   I started with two  16mm thick x 120mm round "dropouts" from the local scrapyard and machined a hole in each for the outlet. In one 1 machined out a concave section where it would fit over the dome. (See pic). I then marked the shape of the flange with a piece of self adhesive vinyl and drilled the bolt holes and then tapped the holes in the lower flange.

This work was all done under the watchful eyes of my three faithful assistants, Thai, Smudge and Jinja.

Then with the two bolted together I drilled a series of holes all round the shape to make it easier to cut out with an angle grinder and then started hacking away with the angle grinder until I was pretty close to the shape I wanted.
(Pic 1), (Pic 2) and (Pic 3). Finer shaping was done with an abrasive disk on a rubber backing pad still with an angle grinder and final smoothing was done on my homemade disk linisher. The shape is not identical to the original but remember I did say "reasonable facsimile".  :-)

Next I marked off and drilled the baffle holes in the lower part of the inlet pipe. Before cutting this pipe to length I  loosely assembled and aligned all the parts and welded the bottom dome in place.

Here is a pic of all the bits loosely assembled and beginning to look like something.

Thereafter I cut the inlet baffle pipe to length and welded a nice rusty collar [;-)] to it for the top pipe to locate in and reassembled and welded it all together.  My camera battery also went flat so there are no pics af the last bit of work.

I welded the top flange to the dome and plugged the threaded bolt holes with a wooden dowel while I filled the bit between the "ears" of the flange with welding and ground them to shape with an angle grinder. The "tailpipe" was welded to its flange and the 2 removeable baffle tubes were made. The one with holes is blocked off at it's base and the other is a "freeflow". I welded two lugs with holes to them to aid in removal. Here is a pic.

Here is a pic of it nearly finished. The reflections in the pic make it look a lot worse than it is and there is still a little weld filling and shaping to be done but I'm pretty happy with the result.