PIPE DREAMS

In RC214, Frank touches upon the baffling subject of silencers in his blue BSA Flash test, a thing which I’ve taken more than a passing interest in, because they vary so much.

A few years ago, I collected information on the Burgess absorption cigar-shaped silencers that were used by several manufacturers. The original, very simple design relied upon an internal layer of stuffing held in place by a perforated inner tube the same diameter as the exhaust pipe to absorb the acoustics. This uninterrupted central pipe allowed free flowing exhaust gasses, which didn’t hobble the few horses of my 250s, but cheaper versions which omit the stuffing and introduce baffles are usually very restrictive and often a lot louder.

Do the internals of BSA / Triumph sausage-type silencers vary as much? Robert Murdoch, member

I enjoyed an interesting chat with the Slovakian guy who manufactures new silencers for the very late AMC machines. He’d chopped up an original to see how it worked and simply copied it. Here was an opportunity to see how the pattern silencer compared to the original on the AJS when I bought it. On these, the header pipe is the key: the end is closed, with slots in the sides of the pipe for the gas to head straight outwards into one or two (AMC did both) areas of packing joined by a section of pipe. Which feeds into more packing and into the tailpipe and out to destroy the planet, of course. I also tried the bike with a good condition 1970s pattern silencer, but it was very loud and harsh. The Slovakian replacement sounds very sweet and the engine runs and revs very freely. Mostly... Frankw