AJS & Matchless Owners Club

Mick D wrote:Perhaps it may be good to drill some holes and see how they affect the noise output rather than plugging the pipe straight away.

Yep, drilling the header as Mick suggests should take the harsh crackle off the exhaust. It's not going to make it super quiet, but it should improve the noise without affecting performance. Blocking the end off will increase back pressure, so might affect performance a little.

Please excuse the old man but what is a "header". Are we saying that the original blanked end pepper pot was a waste of time.

Colin

“header” = “downpipe”

There are at least three ways to arrange the end of the downpipe:
1. Straight cut. Noisy. Maximum flow.
2. Pepperpot drillings, open end. Maybe slightly quieter. Maximum flow.
3. Pepperpot drillings, blanked end. Much quieter. May restrict flow.

I recall my G3LS when almost new, back in the 50's had a long pipe that went deep into the silencer. I do not recall if the end was blocked.. Look at the parts list drawing for 1955. In the drawing the end seems to be open. But it shows a row of 10 holes, There must be at least 4 rows = 40 holes. That is a lot more than the 16 mentioned and seen in this topic, for consideration.

Somewhere, sometime, I remember reading that the blanked off pipes had to have holes drilled so that the total area of them was the same as the cross section area of the exhaust pipe. If done in this way I would assume the back pressure would not be affected. It's a lot of small holes though.

Hi

If the pipe has an ID of 1 - 3/4" you would need 32 x 5/16", (8mm), holes - however I'd check the ID of the silencer tailpipe as this may be smaller.

Regards Mick

Just wanted to thank everyone for this thread; I have a ‘58 18CS, and am facing a similar dilemma about making the bike more sociable without choking it.

Cannot go by the drawing in the parts book if total hole dia's = pipe dia. as I believe 350 & 500 had different dia pipes. Holes ay have differed but only one pipe drawn. 350 or 500 ??? I have a rusty old pipe & silencer I had on a 350, I took off over 30 years ago. But cannot get to it without moving a load bikes and bits, to check holes on it.

It happens that I was intrigued by this some years ago because of the big differences in exhaust noise between my bikes. The exhaust pipe and silencer of my very quiet '56 G3LS look original but I am not sure they are. The pipe has 4x10 holes of slightly over 5.5 mm diameter, in the last 12 cm of the pipe. The end is closed. The pipe goes 21 cm into the silencer. The effective holes diameter (translated to one big hole) is sqrt(40)*5.5 mm = 35 mm, which correspond quite well with the pipe ID (see remark Clive).
There is also a similar closed and perforated length of pipe inside the rear end of the silencer. So there again the exhaust gasses have to pass through a series of small holes.

Albert