Very simply the length of the lever arm from the vibrating engine is placing too much load on the semi-rigidly mounted silencer. The fexible joint is too far from the silencer to help. There needs to be another mounting bracket forward of the silencer and a flexible section just forward of that bracket.

I had a very similar problem with a Laverda 3 cylinder motorcycle: the engine was mounted on big silentblocs to isolate vibration but the silencers were rigidly mounted to the frame. The weak point was the 3-into-2 under the engine which continually cracked.

Peter

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