New Game: how'd I roach that piston?
 

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.

http://forums.pelicanparts.com/uploa...1207333224.jpg
http://forums.pelicanparts.com/uploa...1207333346.jpg
http://forums.pelicanparts.com/uploa...1207333457.jpg
http://forums.pelicanparts.com/uploa...1207333528.jpg
http://forums.pelicanparts.com/uploa...1207333592.jpg
http://forums.pelicanparts.com/uploa...1207333645.jpg
http://forums.pelicanparts.com/uploa...1207333676.jpg

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.
http://forums.pelicanparts.com/uploa...1207333802.jpg
http://forums.pelicanparts.com/uploa...1207333923.jpg

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!SmileWavy
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. ***

...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!

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.

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

or too much nitrous and not enough raw fuel.

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..............:D

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.

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.

http://forums.pelicanparts.com/bmw-r1100s-r1200s-tech-forum/352247-ouch.html

http://forums.pelicanparts.com/bmw-r1100s-r1200s-tech-forum/358861-rebuild.html

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

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.

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?

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

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

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.

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

thx jony.

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

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.

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

- Mark

:)

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.

How did your plugs look last change out? I`m just wondering, white with a lot of spatter or brown normal looking? Sorry to see your problem. It can happen to any brand though.

Lane

I'm going to say that the oiler and compression rings all got in perfect alignment and the blow by melted the piston on its journey to the bottom end as long as we're making wild a$$ guesses.

I'd say its a mystery until its solved.

Sorry for the pain in the ass, not to mention your pocket book. Swarty seems to be close on this one. Good luck with the 1150 upgrade.

NO, IT'S NOT... at least not when your boat sits in salt water, trust me!

Thats kinda what it looks like to me too. However detonation is most often seen in the center of the piston. It looks like the top of the piston had been errodeing away for some time before ring failure occurred.

Have you alerted the timing? Running nitro methane perhaps??;)

markjenn, I backed up with a honda. but the forks are out getting re-valved so I got three bikes and none on the road.

I'm definitely sending the injectors out for testing, then cleaning. I really have to hit a firm conclusion on this so I can be sure it doesn't happen again.

I don't think this is a big problem with BMW's. after all part of the mystery is that no one has ever seen this before.

the plugs look great. NGK Iridium.

Nail, that was the first thing we checked. the rings were perfectly placed and other than the obvious showed no wear or other signs of degradation. I think the rings put up a pretty good fight, considering. they were burned clear through or even blasted through the hole on failure.

the injectors seem the best wild ass guess so far. that hypothesis should be easy enough to test though. there were no changes to the timing and the bike ran fine- no detonation that I could feel or hear and the bike always got high test fuel -- but not nitro methane!

ok, maybe not worse than a boat. but still money that could be used elsewhere. Found myself cruzing the want ads for Stearman Biplanes last night; now that's worse than a boat.

If you are serious about this, might also consider a Waco UPF-7. Has the panache of a Stearman but with 4 ailerons.

I run Chevron Techron Fuel System Cleaner through all my motors twice a year...keeps the injector spray pattern in good shape I hope.

I see pistons that look just like yours quite frequently on Wave Runners and JetSkiis, after people let them set over the winter with fuel in the carbs...The carbs clog up with varnish.. then they go out next summer and run them across the lake lean...starving for fuel

Presto... melted piston.

Also...Be sure to check the wiring that runs that injector.... Injector could be good, but resistance from a bad, or dirty connection could cause the injector to not supply enough fuel.













.

But these are two-strokes, right? Completely different animal.

- Mark

In what way Mark? The only difference would be the addition of a little oil in the cylinder.

I can accept people not believing me.. Living in Arkansas doesn't do much for my credibilty, nor does my online clowning/joking persona. You can do a google search for images for pistons... Detonation breaks/fractures the piston and ring lands (the area between the rings) while a lean condition melts pistons, and also causes the piston to expand and then metal transfers from the piston to the cylinder.




Again... The injector may not be getting enough electricty... If the injector checks out good.. be sure to inspect the wiring.

BigScience... You stated that you got Chris Hodson's opinion on the failure... but you never told us what it was??? What did he think caused the failure?

I'm with Bill,

This looks classic lean. In this case, it looks the same, 2 or 4 strokes.
I can't be sure though. It's hard to tell once things get too chewed up.
I too would be interested in what Chris had to say.

Sorry you're having to deal with it though bigscience. What a bite in the ass.

My point is mainly that it is pretty easy to roach a two-stroke with lean jetting, but four-strokes are much more tolerant of abuse in this regard. This engine didn't fail the first time it was fired up after winter and run across a lake, it failed 40K miles after a rebuild. Whatever caused the problem is likely to be progressive and subtle, whereas you can seize most two-strokes in a matter of seconds if you get the mixture way off.

I'm not betting on mixture as the problem.

- Mark

Mark, the rebuild failure history could be completely unrelated and irrelevant and just throwing sand in our eyes. A lean condition could be caused by an injector getting clogged up over the winter, or an injector not getting sufficient power to fire properly, or possibly a fuel pump not providing enough pressure, or a combination due to low system voltage from a broken rectifier.

Wait, lean roaches pistons, that cant be true.

You see my Great Uncles-Cousins-brothers-nephew (that is your sister in Arkansas) :eek: had this new Ford F150 he bought in the 70's and it got 70 miles to the gallon, he was ecstatic. After a month he got a frantic call from the Ford factory that there was an urgent recall on his new truck so he took it in and they changed the carb, after that he could only get 15 MPG. After researching it, he found that Big oil companies had paid off auto makers to not use the special carbs and cut into their profits.

See so it can't be true that lean is bad:rolleyes:

http://www.hashkafah.com/style_emoti...ult/stupid.gif

http://www.laskeyracing.com/shop/breakin.htm


The 2nd half of this page offers further explanation of what lean does.

Yup, It's absolutely CLASSIC looking lean. Sure, it _could_ be something else, as there are a LOT of ways for a motor to fail, but if you actually work on them, you begin seeing patterns. Ones that aren't too hard to I.D.