Broken ringland symptoms
- Thread starter tunapie
- Start date
Try doing a leakdown test. This can point you in the right direction as far as where your compression is going. It is possilble a broken ringland can harm your valves in many different ways.
If you could look at the cylinder walls, with either a bore scope or from underneath with the oilpan off, you could see if there is any scoring of the walls.
But you are looking for the right symptoms...
Hope any of this helps.
If you could look at the cylinder walls, with either a bore scope or from underneath with the oilpan off, you could see if there is any scoring of the walls.
But you are looking for the right symptoms...
Hope any of this helps.
Other than the vapor that came out of the vent tube (the one that vents to the atmosphere in a BBSC install), There was nothing else noticable. A noticable difference in power could not be felt. At the time it happened, because I had not talked to anyone else about the symptoms, I initially thought it was something as simple as a bad pcv valve.
Note - I ended up with only one cracked ring land.
Note - I ended up with only one cracked ring land.
Elite said:
The low compression from a crushed ring land is not related to the valves, but rather the fact that the piston rings in the area of the damage are no longer able to seal. Of course if some chunks of pistons break off an bang around in the combustion chamber then a valve may close on one and be damaged, but that's by no means certain.
With the piston damaged around the rings, high pressure combustion gasses blow down past the rings into the crankcase. That's where your lost compression is going as well. Turn the engine to TDC foe the bad cylinder so the valves are closed. Hook up a leak-down tester to the spark plug hole, block off the valve cover vents on both banks (at the valve cover), and pull out you dipstick. When you apply air pressure it will blow by the bad ring land and be clearly observed and heard at the dipstick. Actually you could plug one cover vent and check for air escaping the other, just be sure none are still connected to the intake. If there is a bad valve you should be able to hear it at the intake or exhaust.
Odds are you have just what you suspect, but it is certainly worth testing.
WOODY said:
Yep, with it running and only one piston bad the vent pipe will have very distinct individual pulses. That alone is typically enough proof with the test outlined above, but you may not want to run it anymore unless you plan to do sleeves anyway.
tunapie said:
There isn't necessarily much smoke when this happens, especially on the street. The oil scraping rings (the bottom double) may not be badly compromised. So the crankcase is pressurized but until some oil gets trapped in a valve cover and forced out the vent into the intake, oil consumption may not increase dramatically.
Dan, from the drivers position, looking rearward, I didn't see anything visually. However, the ECU threw a CEL, which ended up being a code for a bad O2 sensor.tunapie said:
Keep one thing in mind; As soon as I saw the blow-by escaping up from the rear engine hatch vent, I kept RPM's from exceeding 4.5K, becasue I wasn't sure what was happening. So, take my no noticable loss of power statement as a general one, without having induced hard acceleration.
As Steve said, my vent tube blow-by pulsed very distictly.
As to your leakdown test proving inconclusive, could that not be because of the severity, or lack thereof, your particular ring land crack might simply not be as bad as some of ours? In other words, my ring land was non-existant, and maybe a piston from another car that has cracked, but still had some ring land area left, might not allow as much pressure leakage during the test. Just a thought. Steve can probably give us a better idea if that might be possible.
I wish one of us could see your syptoms. One thing I know now, and that's what a broken ring land shows up looking like.
A fellow BBSC'r found that out at XPO. He thought he was running rich until I hopped in his car for a ride. Hated to be the one to break the news to him. 
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On my integra when i cracked the stock ring lands, i got a distinct Putt-Putt-Putt-____-Putt-Putt-Putt-______-Putt-Putt-Putt-______
No Smoke, Drove Ok, Just sounded like it missed at idle.
Pulled the motor apart, and found 1 piston with the ring land completely broke, but the top ring, and second ring held it in place. And on the other 3 pistons i found cracks in the ringlands, but they were still attached to the pistons.
The compression test on the motor was like 185/180/190/75
Didnt do a leak down, as i was too impatient, and pulled the motor apart.
-Ray
No Smoke, Drove Ok, Just sounded like it missed at idle.
Pulled the motor apart, and found 1 piston with the ring land completely broke, but the top ring, and second ring held it in place. And on the other 3 pistons i found cracks in the ringlands, but they were still attached to the pistons.
The compression test on the motor was like 185/180/190/75
Didnt do a leak down, as i was too impatient, and pulled the motor apart.
-Ray
NA1 #2853 said:
Not an NSX with one cracked ring land. Mine didn't miss a beat at idle, and had no putt-putt sound.
Not the best pics, but here's what it looked like:
Thanks for the info all. Looking at the datalog when it happened I did two 3,300 to 4,000 pulls for about 4 sec with af of 12.4/13.2 retard to 17 and boost at 6.5. This was the exact setup I have had for a brief track session and laying into my new found power since NSXPO with the only change was a increase of 1lb boost two days before the event. Most likely my pistons were beat up from a prior ECU experiment/ bad tuner. The boost adjustment on these FI systems is like that evel ring in that elf/dwarf movie calling you to twist it in. "Just 2 more lbs and you will have WAY MORE fun". Dan
Detonation, or atleast in my case.
-Ray
-Ray
That's a bit simplistic. In fact, I have seen ring lands cracked on another engine (not an NSX) where detonation was not involved. That case involved a bowtie engine dropped into a marine application, where the end gaps were not increased as they should have been.NA1 #2853 said:
That said, in my NSX's case detonation was involved, as the pistons show signs on the domes. I never did hear anything, but I was on the highway with some tunes going. My understanding is that the excessive heat from the detonation causes the rings to expand up to the point where the end gaps close. At that point they have to go somewhere for further expansion, so the ring land becomes the path of least resistance.
My understanding is that the excessive heat from the detonation causes the rings to expand up to the point where the end gaps close. At that point they have to go somewhere for further expansion, so the ring land becomes the path of least resistance
i was under the impression that insane amounts of pressure were generated that caused the damage resulting from detonation (and the "pinging"). heat is a big factor for preignition? willing to be corrected if i am misinformed.
woody
i was under the impression that insane amounts of pressure were generated that caused the damage resulting from detonation (and the "pinging"). heat is a big factor for preignition? willing to be corrected if i am misinformed.
woody
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A fellow BBSC'er found that out at XPO. He thought he was running rich until I hopped in his car for a ride. Hated to be the one to break the news to him.
Gene - what prompted him to think it was running rich?
How could you tell that it was something else?
Gene - what prompted him to think it was running rich?
How could you tell that it was something else?
Gene - what prompted him to think it was running rich?
Because the week before he called MB about the symptoms, and Mark said it was probably just running a bit rich and that he would bring him the new SS box and install it while at XPO. I'm sure the conversation was much more in depth than that, but that's what this owner took out of it.
How could you tell that it was something else?
A) He had just explained to me that if I saw some smoke at the rear it was because he was running rich, so that I should not be alarmed. Being that my car recently had blow-by symptoms, it prompted me to look behind as we were pulling out. What I saw was identical to my symptoms, which recently had a leak-down resulting in #4 being bad.
B) At RPM's around 2.5k - 3.5K, while under some load from going up a particular steep incline his car was pinging so loudly that people in other cars heard it. Funny thing is, nothing was heard other than at low RPM.
Because the week before he called MB about the symptoms, and Mark said it was probably just running a bit rich and that he would bring him the new SS box and install it while at XPO. I'm sure the conversation was much more in depth than that, but that's what this owner took out of it.
How could you tell that it was something else?
A) He had just explained to me that if I saw some smoke at the rear it was because he was running rich, so that I should not be alarmed. Being that my car recently had blow-by symptoms, it prompted me to look behind as we were pulling out. What I saw was identical to my symptoms, which recently had a leak-down resulting in #4 being bad.
B) At RPM's around 2.5k - 3.5K, while under some load from going up a particular steep incline his car was pinging so loudly that people in other cars heard it. Funny thing is, nothing was heard other than at low RPM.
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WOODY said:
I have no grounds to correct you. I was just passing on an explanation, that was given me, which may, or may not be correct. Seemed logical to me.
A copy/paste definition of pre-ignition and detonation:
Q: What is pre-ignition?
Defined as: ignition of the fuel/air mixture before the pre-set ignition timing mark. This is caused by hot spots in the combustion chamber, which results from advanced ignition timing, a spark plug that is too hot, high compression, low octane fuel, lean air/fuel mix, insufficient engine cooling, or carbon in the combustion chamber. Pre-ignition and detonation are separate events, but pre-ignition frequently leads to detonation.
Q: What is detonation?
Detonation involves rapid, uncontrolled burning of the air/fuel mixture while the piston is still rising. During normal combustion, the flame front propagates across the cylinder at a controlled subsonic speed with the piston near TDC. During detonation, the flame front goes supersonic and/or collides from different directions. This rapid detonation strikes the top of the piston as it is still being pushed upward in the cylinder by the crankshaft. The shock wave resulting when the detonation flame front strikes the top of the piston causes the piston to rattle in the cylinder. The sound of this shock wave and the sound of the rattling piston is what people commonly refer to as ping. Detonation radically increases cylinder pressure and temperature, and can quickly burn the end of the spark plug. Excessive heat is usually what causes engine damage when detonation is ignored.
Hi Gene,
According to this definition, I interpret it this way. In some ways the two conditions are the same. Something prior to the spark igniting causes the charge to ignite in the cylinder. However, detenation is when the preignition is so early the piston is not still forcing itself upwards( I should say the crank shaft
)
Make sense??
BTW, I was directly behind the car in this discussion at NSXPO, pinging was redily evident.
Thanks,
LarryB
According to this definition, I interpret it this way. In some ways the two conditions are the same. Something prior to the spark igniting causes the charge to ignite in the cylinder. However, detenation is when the preignition is so early the piston is not still forcing itself upwards( I should say the crank shaft
)Make sense??
BTW, I was directly behind the car in this discussion at NSXPO, pinging was redily evident.
Thanks,
LarryB
SJS, I was eluding to the possibilty that peices of piston or ring may be closed on by the valve...
Here's a better explanation of pre-ignition and detonation that Lud posted last summer: http://www.nsxprime.com/forums/showthread.php?s=&threadid=19744
peiserg said:
A short answer would not do justice to the question. One problem is that you are typically checking AFR on a combination of cylinders at once for an average of three or more, so one could be too lean and therefore at risk while the average looks fine. You also need to keep an eye on changes to AFR, sudden or gradual, from things like dirty injectors or filter, aging pump, etc. Then there are times when your intake air temp is higher than normal due to climate or running the car hard, also placing you at greater risk than during tuning or general logging. In all thee cases it helps to know for sure that you tuned it such that the knock sensors are not activated under "normal" conditions, so as to have that safety margin for times when you need it. If they are triggered during your tuning sessions then you may be at the ragged edge already and not know it.
Another problem is that most people tune on a dyno and cover a relatively small area of the total fuel load/rpm map, the rest of which is interpolated. Unless you do lots of variable load logging to check the rest of the map you may have spots where AFR is too lean and starts detonation. Once started it tends to continue even if you then enter a "good" part of the map because it is generating so much heat at the wrong times.
In other words, if you tune to the limit it is very difficult to know, much less enforce, that every cylinder is operating under safe conditions 100% of the time. So tuning for most of us needs to leave some margin for error rather than trying to wring out that last HP. With better programmable ECUs you can trim fuel per cylinder, but that assumes you can test each individually or have reliable information about which ones tend to run leaner or richer than others and by how much. You can also increase how aggressively the knock sensors retard timing, and increase other trims such as IAT or add one for EGT. But for your "basic" bolt-on and drive forced induction you should tune conservatively or you will eventually join the growing line of people waiting for a rebuild.
