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Our 82 model 750 twin has developed a deep inside knock at idle. Big end ? or ? it has done about 70,000 Miles. any ideas ppl ?

It's difficult to diagnose a noise I can't hear, but a big end knock is certainly possible. Does it only knock at idle? A charactoristic of a bad big end bearing is that it will only make noise under a no load condition. In other words, it will not make any noise when accellerating/deaccellerating, or pulling a load. If it is a bad bug end bearing, and you rev it to ~3k-4k rpm in neutral and hold it there, then it should hammer like crazy.

Yeah I knew that not hearing it would be difficult LOL, then again we do live in australia so its even harder !! It doesn't make the noise at idle /low revs when its cold, only when its hot and the oil has heated. I'll try the 3-4 thou rev idea and get back to you. Tks for that.
Although I would say a rebuild is on the cards.( gee that way i can fix the leaking tacho drive finally !! LOl tks again back soon