I know you vultures enjoy carnage as much as the next fella, so check this out and see what kinds of guesses you have as to a cause.
The bike is a 2003 R1100S SBX purchased new by me from Bob’s BMW in Maryland, where I live. Initial maintenance was (thankfully) done at the shop just to make sure I wouldn’t be blamed for anything like what’s below. Subsequent maintenance I did at home- having had an S bike since new in 99 I’m fairly competent if not ambitious.
At 12,XXX miles the bike burned a hole through the left piston. I had the bike towed to Bob’s for warranty work. There just happened to be someone from some BMW corporate office hanging around the free doughnuts when my bike was torn down and the piston removed. The suit pronounced it a fault in the casting, said to cover it all, and that was that. Curious as to why this kind of thing happens to a highly engineered German machine of fifty-years design time, I asked but no one had a clue. But at least there was no trouble dealing with the paperwork and a month later (matched balanced pistons had to be airlifted from Germany) I was on the road. So, this time around both pistons were R&Rd, but the jugs and heads were untouched.
Flash forward to last weekend. The bike now has 51,372 miles on it and I experience that stomach-punch déjà vu that I’m going to miss dinner again. Power just fades away while smoke pours from the rear.
This time, being out of warranty, I towed it to my friend’s shop and lo and behold, the left piston looks like 50 cent’s grill shot.
However, this time the burn was along the side burning the NiCad walls. You can see how it made its way down the side till it hit an oil port, shot aluminum slag all into the underside of the piston and onto the rod, then finally blew. The chip in my hand is aluminum slag that was stuck to the underside of the piston. The shot of the con rod shows the discolored spot where a chip of slag has fallen from it.
cylinder is toast this time.
I have had no metal work done on this bike. It now has (but did not at the time of the 12,xxx failure) Stayintunes, 9 degree sprockets and the matching FIM chip. My shop (not Bob's) tested the head and found it holding pressure at about the rate you'd expect with 50k on the clock. So this effectively rules out a leaking valve blowing a jet of air onto the piston head. (the hole is on the intake valve side).
Any guesses? The service guys at Bob’s had a bunch, but no two were the same. Bob suggested it would be a nice paperweight. Previous tries have been everything from spark advance wrong to con rod too long causing the top ring to bind to leaky valve to micro crack in the head. A service manager at Bob’s said the two incidents are unrelated, which I find unbelievable since this particular bike is the only one anyone at Bob's can remember burning out a piston (without nitrous or some other easy explanation). In fact, no one so far has seen anything similar. So, I turn to you lot, the collective wisdom of all things f’d up with a boxer engine, for a diagnosis -- Ask for information and I’ll give it as closely to the truth as I can remember.
Thanks in advance for your smart ass comments!
Carlos
*** I just got Chris Hodgeson’s opinion, but just for fun I’ll hold on to that until one of you yo-yo comes up with the same guess. ***