Sadly, the horror stories above vindicate my thoughts regarding these bikes. While several of you have enjoyed riding them, the overriding message is still that they are unreliable. I expected by now to have a staunch supporter telling us how many they knew of that had 100 million miles, but no. I have been told by several owners that theirs had done an honest 100,000Km, or in one case miles, but there is only one 750 GT to which I give any credence to. That was a member of our VOCNZ section, recently passed away, but when I first got to know him in the Italian Motorcycle Owners Club in the '70s he rode his GT two up a lot, clocking up the the 100k until a Vauxhall Viva U turned in front of him & the Ducati tipped the Viva over. At that point John stripped the engine, and broke the lead seal on the crank case, while straightening the front end. He had run it on Shell high detergent multigrade diesel engine oil which debunks the international myth started by Steve Wynne about the absolute necessity for straight grade 50 weight.
The real problem with the cranks was pointed out to me by someone with a knowledge of metallurgy & is well demonstrated by Oexing's pic of the rod. In case you hadnt noticed, there is no sleeve inside the rod eye, the rod is hardened & ground like a two stroke rod. At the confluence of the shank & the eye is the largest mass of material. When that is quenched from red hot it is the area slowest to cool, hence slowest to harden. The hardening is likely to be be both softer & thinner. It is also the area of greatest load. It all goes down hill from there.
I have also been shown several of these power plants with failed gear shaft bearing areas. They run crowded rollers straight on the shafts, the rollers pick up the shaft hardening, simply overloaded bearing area. I have also experienced two with failed gearbox main shafts. One was brought to me for opinion prior to purchase. I only rode it long enough to drop it into top gear, at which point the concrete mixer noises started, I handed it back quickly & recommended a trailer! We had another do the same thing a couple of years ago at a National VOC Rally in Central Otago.
So that is enough of the bad news stories, the solution to getting these nice handling bikes back on the road is to track them down & fit Vincent motors.