New Game: how'd I roach that piston?

[bigscience]

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. ***

[signit98]

...did one of th butterflies lose a screw?... it does not take all to much to cause that carnage to a fast moving piston... and - subsequently, with the parts disintegrating - to the rest of the cyclinder... as shown!

[PFFOG]

Looks like possible detonation. The other theory might be that the first time it happened there was a slight out of round condition and the rings were not contacting the cylinder in a small area, thus allowing combustion gases to blow by the ring and deteriorate the ring lands.

[JonyRR]

looks like detonation to me as well.
was one of the timing pickups off or something?
leaking intake manifold boot?

[JonyRR]

or too much nitrous and not enough raw fuel.

[PFFOG]

Or...
synthetic oil.....Oh wait that would be Dino.....
or maybe the wrong tires, should have used Metzelers.........
maybe the wrong tire pressure do you check cold or hot? ..........
Wrong fuel, should run nothing but VP racing stuff, gives you 10 more Hp and smells nice too.........
Maybe the ECU was a Mac, not a PC...............
...........and on and on..............

[bigscience]

signit; all teh screws are there and there are no dents on the piston.

Yeskino, some detonation likely was going on since there is splatter all over the piston head, but the bike ran fine (I didn't hear anything over the 40k miles before it blew this time). The cylinder was checked for round before being put back in last tiem. I suppose I should check it now again.

[pmc847]

Send an email, with pictures attached, to Chris at SJBMW and see what he has to say. He was very helpful when my BCR granaded last year.

Ouch!

Rebuild

[markjenn]

Tough one. Nice pictures and explanation.

I'd vote for some kind of piston defect with the original failure, then something being a bit off in the repair (barrel slightly out of tolerance, poor piston fit, etc.) that eventually bit 40K later. I'd guess the rate of failure in 40K miles of an average "fixed in the field" cylinder with new piston is 10x the rate of the original.

If your service conditions are unusually tough - riding super hard, high ambient temps, lots of stop-n-go traffic, heavy loads, occasional necessity to run regular rather than premium - and the bike has any tendency to ping, then I'd switch and go with the detonation theory for both failures, perhaps exacerbated by some minor issue with the TB, intake runners, MAF sensor, etc.

- Mark

[bigscience]

Jony, timing pick ups are ok and no manifold leaks that we could find (hard to test on a bike that don't run though).

most reasonable guesses tend towards a fuel/air imbalance, and that seems most likely so far. Ignition timing should cause the same condition on both sides, right? the other piston looks fine.

[bigscience]

Markjenn, this was my date bike- no hard runs, just me and some lucky lady off on a lark. I have another bike for thrashing. But I'll try the cylinder for round now and see what I get.

pmc, I have spoken to Chris. Since he's not seen the like before he didn't want to make big pronouncements but his best guess is a bad injector. they will be pulled off today and sent for testing. recommendations as to where?

[wswartzwel]

Looks like it got kinda hot.... like it was running lean. Piston is melted from heat,rather than cracked from detonation....Bad injector?

[bigscience]

nice guess bill. if it checks out you win a pickle.

[JonyRR]

Carlos;
For the premiere injector service and testing go to RC engineering:
http://www.rceng.com/
they can crossreference the stock injectors or go hipo.
good people.

[wswartzwel]

I used logic.... But am guessing it will be a cheap pickle... Since you are fixing to be out some serious bucks

[bigscience]

thx jony.

if I need to replace one injector should I do both? and go with stock, or is there a more expensive option?

[bigscience]

Bill, I'm so broke I can't believe it but I'm trying to make lemonaid here... I'm going to have to rip the pistons, jug and injectors from the whore bike to get this one on the road ASAP. But that means I HAVE to get an 1150 set to get the whore back on the road too. this is worse than owning a boat.

[markjenn]

I back up my BMW with a couple of cheap Suzuki's.

- Mark

[wswartzwel]

Originally Posted by markjenn

I back up my BMW with a couple of cheap Suzuki's.

- Mark

[JonyRR]

Yeah, lean actually makes more sense.
Carlos, for like $25.00 each, send the injectors to RC.
they'll clean them in a bath of solvent while cycling the injector and will tell you if the spray pattern's good or bad.
That's where mine are going as we speak, for the same service.
I think these plug up like the BBS's get dirty, y'know? there's a lot of black carbony stuff in there. Look at what a BBS looks like after 20K miles.