Not head gasket... holed pistons!

[Road_Clam]

The pics of those holed pistons are not from running too lean. Too lean of a mixture heats up the whole crown, and will melt the top of the piston, and cause a siezure in the bores near the top of the crown. Those dime sized holes are from detonation. A combination of bad fuel, and running the bike under hard, prolonged acceleration, will "dime a piston". Could also be your ignition timing is way off.

 

[Suzuki mad]

I've never seen a set of GS pistons with holes in like that before. If I didn't know better I would have said it was a tuned 2 stroke gone bang!

Suzuki mad

 

[Nessism]

The pics of those holed pistons are not from running too lean. Too lean of a mixture heats up the whole crown, and will melt the top of the piston, and cause a siezure in the bores near the top of the crown. Those dime sized holes are from detonation. A combination of bad fuel, and running the bike under hard, prolonged acceleration, will "dime a piston". Could also be your ignition timing is way off.

I agree about the detonation. Ignition timing can definitely cause this to happen, along with using cheap gas and lugging the engine. For some reason I thought that running the engine lean will exasperate the detonation tendency. Wrong?

I had one of the first generation Gpz550's and it detonated like a bitch. I eventually sold the bike because of it (yea, stupid). Timing was not adjustable as I recall and octane boost didn't help. Reliving my past (in my mind), I was wondering if the header I installed messed up the mixture enough to cause the problem? Not sure but maybe relevent.

 

[first timer]

do those ngk plugs even have the little tab that the spark jumps from the electrode to? it looks like they don't, the spark jumping from the electrode to the piston directly would also cause holing. ether way get some newwer pistons with rings, new air filter, check timing and clean your carbs and set back to factory settings and you should be fine.

 

[Fixxxer]

do those ngk plugs even have the little tab that the spark jumps from the electrode to? it looks like they don't, the spark jumping from the electrode to the piston directly would also cause holing.

They have the tabs, it's just a crappy pic. The NGKs and the champions are in equivalent heat ranges, though... and cheap gas? I was running 87 octane, the same stuff I use in my car... does that really make a difference? And as for "hard, prolonged acceleration," I was riding fairly hard, but no where near redline... definitely didn't seem like I was abusing the engine.

 

[80GS750]

after reading all this, im gonna go pull my plugs and make sure mine dont look like that....

the last thing i need is holed pistons after getting my bike just running again...

 

[petelardo]

Though I agree that the visible damage to the pistons was most likely caused by detonation, I'm worried that we will overlook the CAUSE of the detonation. The lack of an air filter allowed too much air to enter the engine, relative to the amount of fuel being delivered by the carburetors... A lean condition can also cause detonation; in fact, detonation occurs at a LOWER temperature when a lean condition exists. If the piston is holed as a result, then obviously, the damage occurs BEFORE temps inside the cylinder can go high enough to show the effects of the lean condition. IOW, bad fuel, engine lugging, and improper ignition timing are NOT the ONLY reasons why detonation can occur.

The stock air filter and airbox are DESIGNED to be restrictive; this allows smaller carb jets, and (presumed) better fuel economy. The smaller jets used under those conditions make it easier for the OEMs to satisfy EPA requirements, which ISN'T so good for the engine... as we can all see, this one now has a very nasty migraine...

I've seen similar piston damage caused by detonation alone, and I've seen similar damage caused by the combination of a lean mixture AND detonation. If the problem was ONLY a lean condition, then I would agree that the entire piston crown would be likely to exhibit damage, but I'd also expect to see some other effects of super-heated gases in the combustion chamber, such as burned / damaged / scorched exhaust valve(s)... I believe the detonation knocked the holes in the piston crowns BEFORE the engine got hot enough to do the damage we associate with a lean condition, but that does NOT mean that a lean condition did NOT exist here. The absence of the air filter caused a lean condition (among other factors); the lean condition allowed detonation to occur at a lower-than-normal engine temperature; the damage done to the pistons by the detonation prevented the cylinders from getting hot enough to cause the damage we associate with the presence of a lean condition.

Nessism and some others are correct; running the engine lean DOES increase the odds of detonation occuring. If anyone would like to test that for themselves, feel free to remove your air filter and ride without it, as some PO did to this GS550. It might take a while, or the engine might fail for another reason before the lean condition causes severe damage, but you WILL damage your engine. Those sparkplugs were long overdue for replacement; MANY factors contributed to this problem, so let us not dismiss or otherwise overlook the EXTREME lean condition that contributed to this. The HOLES certainly do look to be the result of detonation; don't ignore the contributing factor provided by the lean condition.

I sincerely hope that the OP will soon post some good photos of the OTHER two pistons, the ones that are currently intact, so we can do an online autopsy, based on the visual evidence available. I also would like to see photos of the valves in the cylinder head, so we can check them for any obvious signs of damage.

Fixxxer, I do wish you the best resolving this. Do NOT rush into a decision on how to handle this; I hope you'll use the collective wisdom represented here to help guide you in deciding what to do next.

 

[49er]

Though I agree that the visible damage to the pistons was most likely caused by detonation, I'm worried that we will overlook the CAUSE of the detonation. The lack of an air filter allowed too much air to enter the engine, relative to the amount of fuel being delivered by the carburetors... A lean condition can also cause detonation; in fact, detonation occurs at a LOWER temperature when a lean condition exists. If the piston is holed as a result, then obviously, the damage occurs BEFORE temps inside the cylinder can go high enough to show the effects of the lean condition. IOW, bad fuel, engine lugging, and improper ignition timing are NOT the ONLY reasons why detonation can occur.

The stock air filter and airbox are DESIGNED to be restrictive; this allows smaller carb jets, and (presumed) better fuel economy. The smaller jets used under those conditions make it easier for the OEMs to satisfy EPA requirements, which ISN'T so good for the engine... as we can all see, this one now has a very nasty migraine...

I've seen similar piston damage caused by detonation alone, and I've seen similar damage caused by the combination of a lean mixture AND detonation. If the problem was ONLY a lean condition, then I would agree that the entire piston crown would be likely to exhibit damage, but I'd also expect to see some other effects of super-heated gases in the combustion chamber, such as burned / damaged / scorched exhaust valve(s)... I believe the detonation knocked the holes in the piston crowns BEFORE the engine got hot enough to do the damage we associate with a lean condition, but that does NOT mean that a lean condition did NOT exist here. The absence of the air filter caused a lean condition (among other factors); the lean condition allowed detonation to occur at a lower-than-normal engine temperature; the damage done to the pistons by the detonation prevented the cylinders from getting hot enough to cause the damage we associate with the presence of a lean condition.

Nessism and some others are correct; running the engine lean DOES increase the odds of detonation occuring. If anyone would like to test that for themselves, feel free to remove your air filter and ride without it, as some PO did to this GS550. It might take a while, or the engine might fail for another reason before the lean condition causes severe damage, but you WILL damage your engine. Those sparkplugs were long overdue for replacement; MANY factors contributed to this problem, so let us not dismiss or otherwise overlook the EXTREME lean condition that contributed to this. The HOLES certainly do look to be the result of detonation; don't ignore the contributing factor provided by the lean condition.

I sincerely hope that the OP will soon post some good photos of the OTHER two pistons, the ones that are currently intact, so we can do an online autopsy, based on the visual evidence available. I also would like to see photos of the valves in the cylinder head, so we can check them for any obvious signs of damage.

Fixxxer, I do wish you the best resolving this. Do NOT rush into a decision on how to handle this; I hope you'll use the collective wisdom represented here to help guide you in deciding what to do next.

IMO, a good analogy. I'm not surprised that many 550 owners have experineced "dime detonation". The thinness of those stock crowns means that the pistons would be extremely prone to this type of damage. This thin piston crown design with it's large thin valve pockets, allows little chance for good heat disapation, should the ideal operating conditions not be maitained. Any lean condition would cause concern along with the associated detonation.

 

[jimcor]

When you put that bike back together use the correct NGK B8ES plugs in it.

 

[KEITH KRAUSE]

The damage is done and it seems there's different opinions on what exactly happened or if it's a combination of things.
All you can do is check/clean out the motor and replace the parts.
The thing to do is re-tune everything and it shouldn't happen again.
Use the correct NGK plugs...period. Replace the filter and verify the box isn't modified. Verify jetting. Check timing and advance action.
The plug pics aren't the best but the two left side plugs look like the insulators are a tan/brown color. Nothing very lean to me, just dirty/old plugs. The two right side are carbon stained.
A severe lean condition can cause piston holing as you've all said. But the plugs would normally look snow white and the insulators glazed over under that kind of heat. On the other hand, a rich condition or poor spark can lead to excessive carbon deposits and they will start to glow and build up this kind of heat. The two plugs do look carbon stained but a holed piston will obviously compromise combustion and plug reads are useless (for determining correct mixture at the time).
I think the excess heat is related more to poor ignition timing and possibly the plug rating than related to the lack of a filter, though the lack of the filter certainly worsens things. Even though the damage was at cylinders 1 and 3 (correct??) and being fired off different coils set at possibly different timing, I still think this is more electrical related than jetting related. I think the other two pistons weren't far from holing too.
Doesn't matter now if all basic tuning is done right and the correct parts are used.

 

[Road_Clam]

My next question is how was this bike running just prior to failing? Exactly what was the rpm's, and for how long? Did the engine behave like it was starving for fuel? Again, I am questioning the fuel....

 

[Fixxxer]

Immediately prior to failure, the bike seemed to be running fine. Roughly 75 mph in 5th gear, maybe 7000 rpm or so. I had been hearing some popping noises from the exhaust on decceleration, but the bike seemed to be performing great.

 

[Billy Ricks]

Did you ever hear any valve knock under acceleration, especially uphill or lugging the engine from low RPM's? It's that rattle sound you get when you twist the throttle.

 

[Nessism]

Fixxer,
Do you know what detonation sounds like? Lots of older american cars would exhibit this problem so many of us have experienced it. Basically it sounds like marbles are rattling around in the engine. Occurs when the engine is under high load - such as when going up a hill. Most likely to occur when lugging the engine. Based on what happened before you would do well to make sure to avoid this condition - obviously.

 

[Billy Ricks]

Immediately prior to failure, the bike seemed to be running fine. Roughly 75 mph in 5th gear, maybe 7000 rpm or so. I had been hearing some popping noises from the exhaust on decceleration, but the bike seemed to be performing great.

Popping on deceleration is from a lean condition. Either caused by carburation, timing, or both.

 

[Fixxxer]

Here's the other pistons, two and four, respectively. Do these pics shed any more light on the situation? Also, I don't recall hearing anything that sounded like those descriptions of detonation, at least not in the morning of the day the pistons went. However, at the time it actually happened, I was listening to my MP3 player, so if it developed at some point in the 30 minutes prior, I may not have heard it depending on how loud it actually is. But from what I could hear and feel, there were no indications that the bike was running poorly prior to the instant power loss.

 

[49er]

Here's the other pistons, two and four, respectively. Do these pics shed any more light on the situation? Also, I don't recall hearing anything that sounded like those descriptions of detonation, at least not in the morning of the day the pistons went. However, at the time it actually happened, I was listening to my MP3 player, so if it developed at some point in the 30 minutes prior, I may not have heard it depending on how loud it actually is. But from what I could hear and feel, there were no indications that the bike was running poorly prior to the instant power loss.

The piston in the right pic is so close to blowing through as well. That ash grey colour is the last sign before melting through. The crown rim near the inlet pocket has partially melted. The burn off rate/timimg of burnoff looks the likely cause of the extra heat.
Besides being a dangerous practise, listerning to music while riding can be very costly exercise.

 

[Suzuki mad]

Looks to me that the right hand one was about to expire and the left hand one is well on the way to melting point when the engine stopped.

Seems like you need 4 pistons and rings.

It would suggest that the lack of air filter, ignition timing and a fuel problem have caused this.

When she's rebuilt, check the fuel level in the float chambers, the engine's timing, stick an air filter back in and run her on some better grade fuel. Might also be worth your while cleaning and checking the oil pump too.

We run 95 octanes for Unleaded fuel here in the UK without problems.

Suzuki mad.

 

[Fixxxer]

Well, I won the pistons and block on ebay... Sure, new ones would have been better, but they're $40 each... $160 total vs. $7 for these. New rings will add $98, of course, but I'd still need to get rings if I bought the new pistons anyway.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&sspagename=ADME%3AB%3ABCA%3AUS%3A11&viewitem=&item=320131499956

Now, is there any reason I should use the block that these pistons come with, or is it ok or better to use the original block from my engine?

 

[petelardo]

Some things for you to think about...

Some things for you to think about...

To answer your question, examine both blocks; look for ANYTHING that doesn't seem normal. Check the cylinders; light scrapes can be honed out, but gouges will present new problems, and you'd need oversized pistons, so if you're not sure of what you're looking at, take BOTH blocks to the machine shop that will do the work, and ask them to advise you. If the deck isn't flat (might be warped from heat) or has other problems, you need to find out BEFORE you put money into it, so once again, do NOT rush this. The photo of the block shown on eBay doesn't reveal enough detail to make any call on it, so keep your options open.

Have someone knowledgeable examine the eBay pistons; right now, you don't know if they're actually serviceable or not. The crowns have a coating of carbon, so you won't know what you're dealing with until they're clean. The pistons need to be miked to be sure they are round, not ovoid; you have to be sure the ring grooves aren't damaged, and that they're structurally sound before you can go any further, so don't have any work done on your original block until the pistons have a clean bill of health. If even one is defective, you'll be dead in the water until you get a replacement.

KEITH KRAUSE has mentioned that the plugs don't seem to show the effects of a severe lean condition, and he's right, but he ALSO mentioned that the condition of the plugs are really no help in diagnosing this, and he's right about that, as well...

I think most (hopefully ALL) of us will agree that detonation knocked the holes in those pistons; my thanks to 49er for reminding me of the term "dime detonation" to describe the damage to the piston crowns - my rusty old brain let me down while I was trying to recall it... Though we can't rely on the condition of the plugs to help us diagnose this, those holed piston crowns indicate that carbon buildup was NOT much of a factor here, if it existed at all.

As I've already stated, detonation will occur at a LOWER than expected temperature in the presence of a lean condition. Some may think that a lean condition will ALWAYS show piston slag welded to the cylinder walls, or some other CLASSIC (catastrophic) signs of a lean condition, but I want to emphasize once again that in the presence of a lean condition (as evidenced by the CLEAN piston crowns and cylinder walls, and the fact that the engine was run WITHOUT an air filter), detonation will occur at a LOWER temperature than it does under "normal" conditions. The resulting engine failure PREVENTS the TYPICAL damage we expect to see in a "classic" lean condition, when detonation is NOT a factor... The detonation occurred BEFORE the cylinder super-heated, which is why we DON'T see the "classic" signs of an extreme lean condition...

Logically, (as Keith mentioned) this is all water under the bridge; the damage has been done, and now Fixxxer has to make some decisions about how he wants to deal with this. I've been checking the pictures he posted recently, and those other pistons aren't too pretty, but I've seen worse...

Of course, this could be a LOT worse; at least no one got hurt... Not that I want to point out the obvious here, but so far, Fixxer has admitted to riding on a bald tire, and listening to music while riding, so maybe this breakdown will give him time to think about his attitude towards motorcycling while he rebuilds / replaces the engine. I imagine we've all lost friends who made bad choices while riding; I'd only had my motorcycle endorsement for four years when my friend Jeff was killed in August of 1986. The police report said he'd had ONE beer within one or two hours before the accident, and it must have been enough alcohol to affect his judgment, because he decided to ride anyway. He was only 21, the only son of a Chrysler worker who lived north of Detroit...

There have been others since then, but as smart as they were, they were all guys who did stupid **** around the clock, so I didn't have much hope for many of them surviving long enough to see the far side of 30... Jeff was the only one of us who didn't push his luck at every opportunity, but I'm still here, and he's not. Crazy as I might be, I've NEVER ridden impaired; he ONLY did it once...

Saturday I attended a birthday party for a little girl, who just turned five. She's the granddaughter of a friend who only began riding a few years ago. His older grandkids all wanted to know how many scars / broken bones I've acquired; the broken bones have all healed years ago, because I finally figured out what NOT to do on a motorcycle. Seems they were very impressed by the list: leg, ankle, five of eight fingers (no thumbs broken yet), collarbone, wrist, four ribs, dislocations of the knee, thumb, and OTHER wrist (I wasn't a very good dirt rider, and didn't always wear my gear)... The scars I COULDN'T show them are the ones I carry from attending the funerals of people I cared for, at least one of whom should still be here today...

Fixxxer, I still hope you'll find the time to post a photo or two of the cylinder head, so we can take a look at the valve faces... I realize you might have other things to do, but I'm sure many who are following this thread would appreciate it... In the meantime, I hope you'll think about life and death, especially YOUR life and death; what would your parents say if you were killed riding while listening to "music"? Do you think they'd be happy knowing that you died because you just couldn't live without an MP3 player torturing your eardrums for a few hours? How do you think your girlfriend would feel if you died that way? You can fluff up a coroner's body bag just as well as the next guy, but no one who reads this forum would consider that some type of accomplishment; we'd just list it as ANOTHER needless tragedy... the more cynical among us would say, "Darwin was right", and tell the rest of us that we should be thankful that you haven't fathered any children yet...

One thing OLD motorcyclists know is that the REAL music is in the RIDE; let's hope you start to rethink your approach to motorcycling and life, or you'll only be repairing the motorcycle to use as the instrument of your own demise... I'd like to think you'll learn from this and have a long, happy life, but that won't happen if you don't realize just how lucky you've been so far... Think about the pain your death would cause OTHER people... yes, I know, I'm asking a YOUNG guy to think about someone ELSE for a change, and I know what the odds are of that actually happening, because I was YOUR age a LONG time ago. While you're thinking, think about how unnatural it is for a parent to bury a child, then ask yourself if you REALLY want to make YOUR parents endure that kind of pain... Oh, wait, I forgot, I'M so OLD that I've completely forgotten that people YOUR age are indestructable, or at least, they THINK they are...

As you've already seen, you can only run a lean condition for so long... sooner than you think, there is a price to be paid for doing it. You can repair the damage to the engine, and replace the holed pistons; your family and loved ones will NEVER be able to repair the hole in their lives your death would cause. You need to think about the PAIN your death would bring to the lives of the people who love you; that pain NEVER goes away, and YOU would be responsible for the agony your family endures...

Motorcycling and life are risky enough; those of us approaching retirement age have had to learn the HARD way to minimize certain risks, to improve our chances of survival. If my brother (a cop) ever went on patrol without his vest, I'd KICK HIS ASS to make sure he didn't do it again. There are ENOUGH things you CAN'T control while riding; you don't have ANY control over the drinkers and the druggers who are driving on the same road with you, you can't control the weather, you can't control ANYTHING except yourself and your behavior, so please learn from this...

I have to wonder about something; you seem to have realized that riding on a bald rear tire wasn't the most intelligent thing you've done recently, but would you have ridden on a bald FRONT tire? Would you have taken a passenger with you, knowing you had a bald tire? I realize you haven't been riding very long, but if you don't have enough self-control to wait until you have a SAFE motorcycle to ride, maybe you should put that GS in storage for a while...

According to you, Michigan Tech is two miles past the end of the earth; according to me, the Cemetary of No More Second Chances is just a little ways past that... let's hope you learn enough from this that you don't end up taking an eternal dirt nap there any time soon... losing you is something none of us want to think about, so you need to give this some thought...