I've been complaining about this buzz I've been experiencing on my machine (not the good kind of 60's buzz either) at around
3500 - 4500 rpm.
My engine, according to M Pitman's recommendations, is solid mounted into the frame using bespoke alloy spigots to replace the rubber engine mounts and has been surprisingly vibration free until recently. These spigots have been siliconed into the engine.
Back in 2002 M Pitman also suggested that I strengthen the Engine Stays but I was at a bit of a loss to know how and did not take this advice.
I was giving the big girl a tub on Sunday and noticed this on the right hand Engine Stay.
Fortunately, I have several pairs of these brackets "in stock" and was able to replace the cracked unit with a fresh one.
I have also used slightly bigger HT bolts throughout and needed to drill out the holes accordingly.
So now - to repair and strengthen a pair to be re-fitted.
I am going for a squirt today and hope that the buzz has disappeared.