My friend Ian has disassembled his high mileage 850. This is the first time the bottom end has been apart so all of those parts are original and have done the full 120,000 miles. Here's his note to me Hi Glen, Feel free to share with your blog (please send the link). This is after 120k miles. I got the bike at 13k miles (40 years ago this June), new pistons (+0.020”) and rebuilt head at 55k or so miles. I used to change the oil and filter every 1,000 or 1,500 miles so I suspect that made the difference. I think the deposits in the timing cover are from the Castrol straight 40W I ran for years.