I only rode 13 miles on 9/17, our day riding around Yellowstone and then headed for Jackson Hole, WY, and then didn't ride yesterday going to Mountain Home, ID. I won't be riding today, going to Burns, OR, either. Here's where we are.
Leaving the Lake Lodge in Yellowstone, it was about 30 degrees F outside. The controls were stiff and the fog would ice up on the outside of my helmet visor. Pretty quickly, the bike seemed to have no power, and even while wearing earplugs, I could hear that it was making some pretty loud noises out of the right side.
At a roadside pullout, I verified the static timing and then made sure that the valves were adjusted correctly (the engine cooled down quickly!) There was little else to do but remove the head, and when I did, I found what you see in the photo above: the piston was cracked across the face. Also, when I kicked the engine over, the piston face didn't move. It turned out to be broken around the oil control ring landing.
Fortunately, the piston pin was still in the intact piston skirt and the connecting rod hadn't flailed around inside the cylinder, but there was still a relatively deep mark about 1" long around the circumference of the bore, maybe 1.5" down from the top.
Bits of rings on the end of a magnet, and the broken piston on the ground, next to the floorboard
In Jackson Hole, we tried to minimize the scratch with some emery cloth and about 30 strokes of a honing brush. After that, you can feel but not catch your fingernail on the scratch. I had some old, used pistons and we picked the best one to install. But the engine made a loud noise from the right side and vibrated through the footboard on even light loads.
So we decided not to run to Mountain Home, and instead drive there in hopes of installing my freshly bored set of cylinders with their pistons/rings/valves. We got in a bit before 1pm and quickly disassembled the cylinders and started moving over the valve springs, keepers and collets. This is where we hit the wall: the new valves have larger diameter stems than the old, and no groove in them for the lip on the inside of the collets. I have no spare collets. We talked to a couple machine shops in Mountain Home, but they couldn't do the work needed to modify the valve stems. We hope to find a shop in Boise today that can modify them to accept the collets, so we can continue tomorrow in Burns, OR.
Also, while the machine was standing forelorn next to the van with its top end removed, a passerby mentioned that the right connecting rod looked bent to him. He had good eyes. I brought a set of V blocks and it appeared that the rod was about 5 degrees off. Did this cause the piston failure, or did the piston failure cause this? We don't know. But with a stout punch through the piston pin, Steve was able to straighten the rod so that the pin pulled up flat on the V blocks. There was little else to do but pray that straightening the rod would eliminate the noise in the right cylinder, so we reassembled the bike and fired it up, but there still was a loud piston slap from the right cylinder (although the vibration seemed to be gone).
So, we hope to put on the new cylinders today and ride the bike around some to break in the bore and rings.